Description.

The outer margins of the wings are strongly and irregularly dentate, excavated and angulated. The upper side of the wings has a bright orange ground colour, decorated with brown marks and light spots on the edge. The reverse is marbled with brown. Folded, the butterfly looks like a dead leaf. The hindwings have on the reverse side a white spot usually in the shape of C.  The sexual dimorphism is slight and concerns the intensity of the coloration, the silhouette and the size, the male having a wingspan of 22 to 24 mm. and the female of 25 to 26 mm. The seasonal dimorphism is more marked: the first generation ( "hutchinsoni" form, May-June) has the upperside fawn orange and the underside brown-gold and the hindwing bears distally a broad dark red-brown area in which is situated a row of light brown hastate spots, the underside is dark, being either unicolorous or prominently marmorated., while the second generation (form "c-album" (July, in autumn and spring after overwintering) has a more reddish upper and dark brown underside (ground-colour is less bright). In the summer-form the wings are less dentate, and the hindwing has a narrow dark submarginal band, near which stands a row of light lunules proximally bordered by a band of brown arcs; the underside is of a paler colour, being less distinctly — sometimes, however, very prominently — marmorated and shaded.

Taxonomy and phylogeny.

The comma belongs to the family Nymphalidae, the largest family of butterflies with 13 subfamilies. Within the genus "Polygonia", a sister-group relationship between "P. c-album" and "P. faunus" is strongly supported by larval development analysis and synapomorphies. In both species, the adults and larvae have similar polyphagous habits. The genus "Polygonia" is also closely related to the genera "Kanisha" and "Roddia", each containing a single species: "K. canace" and "R. l-album".

Geographic range and habitat.

The comma inhabits areas including Europe, North Africa, and Asia. It is primarily a woodland butterfly, living in low-density forests with sunshine and moist soil. Specifically, the species is commonly found in the woodland, country lanes, and garden areas of Norway, Sweden, and Great Britain. As a food generalist, or polyphagous species, comma butterflies can feed upon a variety of host plants, leading to widespread ranges across continents. In response to climate change, they are also undergoing range expansion.

Subspecies.

The following subspecies are found in the indicated parts of the comma's range:

Food resources.

Larval host plant preferences and selection.

For comma butterflies, food resources consumed during development are the primary source of nitrogen and protein during adulthood. Because they feed exclusively on plants, making them a phytophagous species, the quality of plants upon which the larvae feed is strongly correlated with their future fitness. The larval form is often divided into five developmental stages known as instars. Although during the first three instars larvae are observed to remain almost entirely upon the underside of leaves, the fourth and fifth instar larvae are more active in obtaining food resources. The later instar larvae are specialized feeders and favor several host plants during the larval stage: "Urtica dioica", "Ulmus glabra", "Salix caprea", "R. uva-crispa", and "Betula pubescens". While pupal weight and overall larval survival rates are similar among larvae regardless of host plant, the larval development times differ significantly. As a result, larvae prefer feeding on plants that allow them to develop in the shortest amount of time. Larvae reared on "U. dioica" demand the shortest development time and is thus favored over other plants. On the other hand, "B. pubescens" is at the bottom of the host plant preference hierarchy. Favoring plants in the family Urticaceae is speculated to have originated from the species’ ancestors, providing an explanation for larval preference for "U. dioica". Within the "U. dioica" plant, larvae are not shown to differentiate between high quality (fresher) and low quality (wilting) nettles, a pattern expected of a polyphagous species.

Reproduction and life history.

Mating.

Mating system.

Comma butterflies have a polyandrous mating system where females mate with multiple males to receive the necessary amount of sperm to fertilize their eggs. The polyandrous female distributes her matings equally over her lifetime, so males' mating success increases proportionally to their lifespan. The mating success of both sexes is correlated to the duration of an individual's life, so no difference in mortality rates is observed between males and females.

Female mate choice.

Females exercise mate choice before, during, and after mating and can distinguish between males who were reared on high-quality versus low-quality host plants. The ability to recognize adults reared on higher quality host plants is selected for because males fed better plants during development provide superior nuptial gifts. In comma butterflies, nuptial gifts are edible spermatophores containing spermatozoa and nutrients. When comparing the two common host plants "U. dioica" and "S. caprea", females preferentially choose to mate with males reared on "U. dioica", because these males have higher protein content and increased spermatophore production.  Females preferentially mate with males which provide larger investments, in the form of nuptial gifts. When females mated with males with higher-quality nuptial gifts, they not only allocate more resources to egg production but also use the resources to improve their own reproductive success. The investments can be used to increase female life expectancy, female maintenance, and future reproduction. During each mating, males allocate a constant amount of investment towards each nuptial gift, indicating that male mate choice does not play a role in allocation of resources.

Oviposition.

Females recognize and select a host plant carefully before laying their eggs upon it, generally favoring host plants where larval development time is minimized. Akin to the preferred host plants for larvae, females prefer plants in the order Urticales. Despite the overall preference for plants leading to short larval development, host plant preference variation between females exists. Although the partiality for certain plant species appears to be inherited across populations, the pattern is not significant within a single population. This pattern of deviation results from the open population structure with high gene flow.

Parent-offspring conflict.

In theory, females would prefer host plants where their offspring performance is maximized, and the larvae would benefit from being able to feed on the best resources nearby their hatch site. However, this is not always observed in nature due to external factors such as predators, parasites, and pathogens. Instead, there is a trade-off between female host plant preference and larval fitness in many species of butterfly. In "P. c-album," instead of accepting the host plant that the female selected, first instar larvae leave their hatch site in search of alternative food sources. Larvae that stay on the inferior host are not only smaller, but also have lower survival and growth rates.

Egg mass.

Unlike female host plant preference, egg mass is not shown to be sex-linked. Instead, egg mass is most likely controlled by additive autosomal genes, where the egg sizes of offspring are intermediate compared to its parents. The type of host plant chosen during the larval stage is not correlated with their offspring's egg mass, indicating that egg size is not related to fitness.

Life history.

Egg.

Females lay their eggs on a variety of host plants, preferring those that minimize larval development time. Unlike some butterflies who lay their eggs in batches, comma females often lay their eggs singly. After each egg is laid, the female scouts out other possible host plants before determining the site of her next egg. The eggs are green when first laid, and gradually turn yellow and ultimately grey before hatching, which generally takes four to five days. Although the female can allocate more resources into egg production based on the nuptial gifts received by mates, the total number of eggs laid or the mass of the eggs are altered based on the host plant. A lack of correlation suggests that neither egg quantity nor egg mass indicate future fitness for the offspring.

Larva.

The larval period is separated into five distinct stages or instars. During the first three instars, the comma larvae have a cryptic appearance to avoid detection while they primarily stay on the underside of leaves. Fourth and fifth instar larvae search for food more actively. However, the beginning of the fourth instar also marks the development of black, white, and orange patterns. To avoid predation despite its conspicuous appearance, the larva develops strong spines along its body. The larvae have a continuous white marking along their backs to mimic bird droppings. In its final instar, the white colouration disappears but the spines persist.  Three possibilities describing why spines may develop during later instars are as follows: smaller larvae cannot sustain the spines, larger larvae benefit more from spines as their predators shift from invertebrates to vertebrates, or because an effective spine pattern cannot be achieved upon the surface area of the smaller larvae.  Aside from the formation of spines, no other defence against predators appears to be present. While fourth and fifth instar larvae are rarely preyed upon by the same predator, removal of the spines leads to repeated predation, indicating that no chemical defence mechanism exists to deter enemies.

Pupa.

"P. c-album" adults undergo one of two morphs: the directly developing morph or the diapausing (delayed development) morph. For both males and females, directly developing adults have a shorter pupal time of around 10 days, whereas the diapausing adults spend over 11 days pupating. Additionally, the pupae whose adult stage would enter the directly developing morph had larger pupal weights, consistent with the notion that the lighter morph allocates more resources towards maturation and reproduction.

Adult.

Full-grown comma butterflies have a wingspan of about 45 mm or 1.8 inches. The name comma butterfly derives from the small white 'C'-shaped marking resembling a comma on the underside of its wings. Commas can exhibit both mimicking and polyphenism, a phenomenon where multiple morphs exist in a population. Due to their orange and dark brown/black appearance, the butterflies resemble fallen leaves when their wings are closed. Adults can also undergo one of two morphs: the directly developing morph or the diapausing morph. During the directly developing morph, the butterflies mature sexually at a rapid rate. Females undergoing this morph oviposit in the summer, leading the phase to also be referred to as the summer morph. Butterflies portraying the summer morph have light coloured undersides. The diapausing morph, also known as the spring or winter morph, occurs when the female enters a reproductive diapause, a time when sexual maturity is postponed, and hibernates before ovipositing in the spring instead. During the diapausing morph, the undersides of the wings are much darker.

Predators, parasites, and diseases.

Predators.

Because of their wide distribution around the world, comma butterflies have a variety of vertebrate and invertebrate predators, including blue tits, chickens, and other birds.

Parasites.

The two main parasites that have been known to affect comma butterflies are "Glypta erratica", a type of stem borer in "Eupatorium", and "Pteromalus vanessae". "P. vanessae" often oviposit in the larvae of butterflies such as "P. c-album" and "Nymphalis antiopa".

Diseases.

"P. c-album" are known to be infected by cytoplasmic virus diseases. The disease infection usually starts in the cytoplasm of the midgut and progresses throughout the foregut and hindgut as well.

Antipredator adaptations.

Larva.

The first three larval instars are camouflaged, the dark colours making the larvae less vulnerable to detection. In the fourth instar, the appearance of the larval body is relatively more colourful with white, black, and orange aposematic patterns. A white stripe along its back mimics the pattern of bird droppings, further displaying protective colouration of the species. During the transition between the third and fourth instars, the larvae also develop strong spines along their backs. Decreased predation by birds on "P. c-album" third-instar larvae has been shown compared to other larval stages, indicating that the spines increase defence. However, this appears to provide limited protection as some birds were able to consume the larvae despite the appearance of spikes.

Adult.

Adults also make use of camouflage. The underside of adult wings mimic the patterns of a fallen leaf. The similarity is further exaggerated by the irregular wing edges, not resembling a typical butterfly, that are characteristic of the genus "Polygonia". The butterflies can also undergo one of two morphs: directly developing (summer) or diapausing (spring/winter). The diapausing morph is triggered when resources are allocated to survival, resulting in a less conspicuous, darker appearance of adults to avoid predation.

Physiology.

Diapause.

Under cold winter conditions, adults can undergo diapause, a period of delayed sexual maturation to maximize survival. The diapause morph is based upon the length of the day that the larvae experienced during the development stage of the life cycle. The diapausing morph is more commonly observed in "P. c-album" butterflies inhabiting south Europe, North Africa, and Asia. The threshold for the photoperiod triggering diapause is primarily due to autosomal genes but may also be influenced by sex-linked genes and/or parental effects. Females tend to enter a diapause based on a photoperiod that is intermediate to the parents, and males are more likely to enter diapause than females. This indicates that males and females have evolved different optimal lifecycles. Females profit from larger body size, because it is correlated with fecundity whereas male fitness is not related to size.

Thermoregulation.

Although dark appearances such as the early instars and the diapause morph are commonly seen in species as a means of thermoregulation, the behaviour of commas makes the theory unlikely for this species. During the first three instars, the cryptically coloured larvae spend most of their time under leaves, limiting their exposure to the sun. Although the later instar larvae are more dispersive in search of food resources, basking is very rarely observed. Thus, their body temperatures do not elevate dramatically in the presence of sunshine, decreasing the effect that dark exteriors customarily have on biological processes such as metabolism and development rate. However, "P. c-album" larvae are observed basking during the two later instars. This may be explained by the resemblance that the later instar larvae have to bird droppings, which would limit predation despite increasing exposure to predators. Thermoregulatory behaviours may have a much more pronounced effect on later instar larvae but do not appear to affect the first three larval stages.

Polyphenism.

Comma adults are dimorphic. The two phases are the directly developing morph (summer morph) and the diapausing morph (winter/spring morph). The two morphs are determined by autosomal genes, which determine which phase the adults will undergo based on the length of the day experienced during the larval stage. During winter, the length of the day is short, and butterfly survival rate is lower. To allow the adults to survive through the cold winter and oviposit during the spring, the adults go through the diapausing morph which feature darker wings for greater protective colouration during hibernation. When the photoperiods are longer during summertime, the adults go through the directly developing phase with a lighter appearance. The lighter appearance is attributed to fewer resources allocated to producing a protective appearance and more resources used to assist reproduction.

Interactions with humans.

Climate change.

Climate change has dramatically affected the habitat ranges of the comma, encouraging range expansion and feeding upon a wider variety of host plants. In Britain, comma butterflies have shown the greatest shift in habitat and feeding resources, altering its preferred host plant from "H. lupulus" to "U. glabra" and "U. dioica". The movement of the distribution appears to be following a change in climate. Although not a migrating butterfly species, the butterflies at the edges of the range show much higher dispersal tendencies than those living within the range.

Population change.

In the 19th century, the British population of the comma crashed, possibly as a result of reduced hop ("H. lupulus") farming. From about 1930 the population recovered, and the comma is now one of the more familiar butterflies in Southern England. It is also found in Scotland and in North Wales. Since the 1970s in Britain, specialist butterflies have decreased in population as their preferred habitat and host plants area becomes smaller. On the other hand, generalist species such as "P. c-album" have started to expand their range. In particular, comma butterflies have expanded along the northern edge of their range.

Polygonia c-album, the comma, is a food generalist (polyphagous) butterfly species belonging to the family Nymphalidae. The angular notches on the edges of the forewings are characteristic of the genus "Polygonia", which is why species in the genus are commonly referred to as anglewing butterflies. Comma butterflies can be identified by their prominent orange and dark brown/black dorsal wings.

Le Robert-le-Diable (Polygonia c-album) est une espèce paléarctique de lépidoptères de la famille des Nymphalidae. Commun en Europe, ce papillon est connu pour sa silhouette particulière, avec ses ailes très découpées.


Details of the Data Assimilation Process.

Classically, data assimilation has been applied to chaotic dynamical systems that are too difficult to predict using simple extrapolation methods. The cause of this difficulty is that small changes in initial conditions can lead to large changes in prediction accuracy. This is sometimes known as the butterfly effect – the sensitive dependence on initial conditions in which a small change in one state of a deterministic nonlinear system can result in large differences in a later state.  At any update time, data assimilation usually takes a forecast (also known as the first guess, or background information) and applies a correction to the forecast based on a set of observed data and estimated errors that are present in both the observations and the forecast itself. The difference between the forecast and the observations at that time is called the departure or the innovation (as it provides new information to the data assimilation process). A weighting factor is applied to the innovation to determine how much of a correction should be made to the forecast based on the new information from the observations. The best estimate of the state of the system based on the correction to the forecast determined by a weighting factor times the innovation is called the analysis. In one dimension, computing the analysis could be as simple as forming a weighted average of a forecasted and observed value. In multiple dimensions the problem becomes more difficult. Much of the work in data assimilation is focused on adequately estimating the appropriate weighting factor based on intricate knowledge of the errors in the system.  The measurements are usually made of a real-world system, rather than of the model's incomplete representation of that system, and so a special function called the observation operator (usually depicted by "h()" for a nonlinear operator or H for its linearization) is needed to map the modeled variable to a form that can be directly compared with the observation.

Data assimilation as statistical estimation.

One of the common mathematical philosophical perspectives is to view data assimilation as a Bayesian estimation problem. From this perspective, the analysis step is an application of Bayes' theorem and the overall assimilation procedure is an example of recursive Bayesian estimation. However, the probabilistic analysis is usually simplified to a computationally feasible form. Advancing the probability distribution in time would be done exactly in the general case by the Fokker–Planck equation, but that is not feasible for high-dimensional systems, so various approximations operating on simplified representations of the probability distributions are used instead. Often the probability distributions are assumed Gaussian so that they can be represented by their mean and covariance, which gives rise to the Kalman filter.  Many methods represent the probability distributions only by the mean and input some pre-calculated covariance. An example of a direct (or sequential) method to compute this is called optimal statistical interpolation, or simply optimal interpolation (OI). An alternative approach is to iteratively solve a cost function that solves an identical problem. These are called variational methods, such as 3D-Var and 4D-Var. Typical minimization algorithms are the Conjugate gradient method or the Generalized minimal residual method. The Ensemble Kalman filter is sequential method that uses a Monte Carlo approach to estimate both the mean and the covariance of a Gaussian probability distribution by an ensemble of simulations. More recently, hybrid combinations of ensemble approaches and variational methods have become more popular (e.g. they are used for operational forecasts both at the European Centre for Medium-Range Weather Forecasts (ECMWF) and at the NOAA National Centers for Environmental Prediction (NCEP)).

Weather forecasting applications.

In numerical weather prediction applications, data assimilation is most widely known as a method for combining observations of meteorological variables such as temperature and atmospheric pressure with prior forecasts in order to initialize numerical forecast models.

Why it is necessary.

The atmosphere is a fluid. The idea of numerical weather prediction is to sample the state of the fluid at a given time and use the equations of fluid dynamics and thermodynamics to estimate the state of the fluid at some time in the future. The process of entering observation data into the model to generate initial conditions is called "initialization". On land, terrain maps available at resolutions down to globally are used to help model atmospheric circulations within regions of rugged topography, in order to better depict features such as downslope winds, mountain waves and related cloudiness that affects incoming solar radiation. The main inputs from country-based weather services are observations from devices (called radiosondes) in weather balloons that measure various atmospheric parameters and transmits them to a fixed receiver, as well as from weather satellites. The World Meteorological Organization acts to standardize the instrumentation, observing practices and timing of these observations worldwide. Stations either report hourly in METAR reports, or every six hours in SYNOP reports. These observations are irregularly spaced, so they are processed by data assimilation and objective analysis methods, which perform quality control and obtain values at locations usable by the model's mathematical algorithms. Some global models use finite differences, in which the world is represented as discrete points on a regularly spaced grid of latitude and longitude; other models use spectral methods that solve for a range of wavelengths. The data are then used in the model as the starting point for a forecast. A variety of methods are used to gather observational data for use in numerical models. Sites launch radiosondes in weather balloons which rise through the troposphere and well into the stratosphere. Information from weather satellites is used where traditional data sources are not available. Commerce provides pilot reports along aircraft routes and ship reports along shipping routes. Research projects use reconnaissance aircraft to fly in and around weather systems of interest, such as tropical cyclones. Reconnaissance aircraft are also flown over the open oceans during the cold season into systems which cause significant uncertainty in forecast guidance, or are expected to be of high impact from three to seven days into the future over the downstream continent. Sea ice began to be initialized in forecast models in 1971. Efforts to involve sea surface temperature in model initialization began in 1972 due to its role in modulating weather in higher latitudes of the Pacific.

History.

In 1922, Lewis Fry Richardson published the first attempt at forecasting the weather numerically. Using a hydrostatic variation of Bjerknes's primitive equations, Richardson produced by hand a 6-hour forecast for the state of the atmosphere over two points in central Europe, taking at least six weeks to do so. His forecast calculated that the change in surface pressure would be, an unrealistic value incorrect by two orders of magnitude. The large error was caused by an imbalance in the pressure and wind velocity fields used as the initial conditions in his analysis, indicating the need for a data assimilation scheme.  Originally "subjective analysis" had been used in which NWP forecasts had been adjusted by meteorologists using their operational expertise. Then "objective analysis" (e.g. Cressman algorithm) was introduced for automated data assimilation. These objective methods used simple interpolation approaches, and thus were 3DDA methods.  Later, 4DDA methods, called "nudging", were developed, such as in the MM5 model. They are based on the simple idea of Newtonian relaxation (the 2nd axiom of Newton). They introduce into the right part of dynamical equations of the model a term that is proportional to the difference of the calculated meteorological variable and the observed value. This term that has a negative sign keeps the calculated state vector closer to the observations. Nudging can be interpreted as a variant of the Kalman-Bucy filter (a continuous time version of the Kalman filter) with the gain matrix prescribed rather than obtained from covariances.  A major development was achieved by L. Gandin (1963) who introduced the "statistical interpolation" (or "optimal interpolation") method, which developed earlier ideas of Kolmogorov. This is a 3DDA method and is a type of regression analysis which utilizes information about the spatial distributions of covariance functions of the errors of the "first guess" field (previous forecast) and "true field". These functions are never known. However, the different approximations were assumed.  The optimal interpolation algorithm is the reduced version of the Kalman filtering (KF) algorithm and in which the covariance matrices are not calculated from the dynamical equations but are pre-determined in advance. Attempts to introduce the KF algorithms as a 4DDA tool for NWP models came later. However, this was (and remains) a difficult task because the full version requires solution of the enormous number of additional equations (~N*N~10**12, where N=Nx*Ny*Nz is the size of the state vector, Nx~100, Ny~100, Nz~100 – the dimensions of the computational grid). To overcome this difficulty, approximate or suboptimal Kalman filters were developed. These include the Ensemble Kalman filter and the Reduced-Rank Kalman filters (RRSQRT).  Another significant advance in the development of the 4DDA methods was utilizing the optimal control theory (variational approach) in the works of Le Dimet and Talagrand (1986), based on the previous works of J.-L. Lions and G. Marchuk, the latter being the first to apply that theory in the environmental modeling. The significant advantage of the variational approaches is that the meteorological fields satisfy the dynamical equations of the NWP model and at the same time they minimize the functional, characterizing their difference from observations. Thus, the problem of constrained minimization is solved. The 3DDA variational methods were developed for the first time by Sasaki (1958).  As was shown by Lorenc (1986), all the above-mentioned 4DDA methods are in some limit equivalent, i.e. under some assumptions they minimize the same cost function. However, in practical applications these assumptions are never fulfilled, the different methods perform differently and generally it is not clear what approach (Kalman filtering or variational) is better. The fundamental questions also arise in application of the advanced DA techniques such as convergence of the computational method to the global minimum of the functional to be minimised. For instance, cost function or the set in which the solution is sought can be not convex. The 4DDA method which is currently most successful is hybrid incremental 4D-Var, where an ensemble is used to augment the climatological background error covariances at the start of the data assimilation time window, but the background error covariances are evolved during the time window by a simplified version of the NWP forecast model. This data assimilation method is used operationally at forecast centres such as the Met Office.

Cost function.

The process of creating the analysis in data assimilation often involves minimization of a cost function. A typical cost function would be the sum of the squared deviations of the analysis values from the observations weighted by the accuracy of the observations, plus the sum of the squared deviations of the forecast fields and the analyzed fields weighted by the accuracy of the forecast. This has the effect of making sure that the analysis does not drift too far away from observations and forecasts that are known to usually be reliable.

3D-Var.

formula_1  where formula_2 denotes the background error covariance, formula_3 the observational error covariance.  formula_4

4D-Var.

formula_5  provided that formula_6 is a linear operator (matrix).

Future development.

Factors driving the rapid development of data assimilation methods for NWP models include:

Other applications.

Monitoring water and energy transfers.

Data assimilation has been used, in the 1980s and 1990s, in several HAPEX (Hydrologic and Atmospheric Pilot Experiment) projects for monitoring energy transfers between the soil, vegetation and atmosphere. For instance:  - HAPEX-MobilHy, HAPEX-Sahel,  - the "Alpilles-ReSeDA" (Remote Sensing Data Assimilation) experiment, a European project in the FP4-ENV program which took place in the Alpilles region, South-East of France (1996–97). The Flow-chart diagram (right), excerpted from the final report of that project, shows how to infer variables of interest such as canopy state, radiative fluxes, environmental budget, production in quantity and quality, from remote sensing data and ancillary information. In that diagram, the small blue-green arrows indicate the direct way the models actually run.

Other forecasting applications.

Data assimilation methods are currently also used in other environmental forecasting problems, e.g. in hydrological forecasting. Bayesian networks may also be used in a data assimilation approach to assess natural hazards such as landslides.  Given the abundance of spacecraft data for other planets in the solar system, data assimilation is now also applied beyond the Earth to obtain re-analyses of the atmospheric state of extraterrestrial planets. Mars is the only extraterrestrial planet to which data assimilation has been applied so far. Available spacecraft data include, in particular, retrievals of temperature and dust/water ice optical ticknesses from the Thermal Emission Spectrometer onboard NASA's Mars Global Surveyor and the Mars Climate Sounder onboard NASA's Mars Reconnaissance Orbiter. Two methods of data assimilation have been applied to these datasets: an Analysis Correction scheme and two Ensemble Kalman Filter schemes, both using a global circulation model of the martian atmosphere as forward model. The Mars Analysis Correction Data Assimilation (MACDA) dataset is publicly available from the British Atmospheric Data Centre.  Data assimilation is a part of the challenge for every forecasting problem.  Dealing with biased data is a serious challenge in data assimilation. Further development of methods to deal with biases will be of particular use. If there are several instruments observing the same variable then intercomparing them using probability distribution functions can be instructive.  The numerical forecast models are becoming of higher resolution due to the increase of computational power, with operational atmospheric models now running with horizontal resolutions of order of 1 km (e.g. at the German National Meteorological Service, the Deutscher Wetterdienst (DWD) and Met Office in the UK). This increase in horizontal resolutions is starting to allow us to resolve more chaotic features of our non-linear models, e.g. resolve convection on the grid scale, clouds, in the atmospheric models. This increasing non-linearity in the models and observation operators poses a new problem in the data assimilation. The existing data assimilation methods such as many variants of ensemble Kalman filters and variational methods, well established with linear or near-linear models, are being assessed on non-linear models, as well as many new methods are being developed e.g. particle filters for high-dimensional problems, hybrids data assimilation methods.  Other uses include trajectory estimation for the Apollo program, GPS, and atmospheric chemistry.

External links.

Examples of how variational assimilation is implemented weather forecasting at:  Other examples of assimilation:

Data assimilation is a mathematical discipline that seeks to optimally combine theory (usually in the form of a numerical model) with observations. There may be a number of different goals sought, for example—to determine the optimal state estimate of a system, to determine initial conditions for a numerical forecast model, to interpolate sparse observation data using (e.g. physical) knowledge of the system being observed, to train numerical model parameters based on observed data. Depending on the goal, different solution methods may be used. Data assimilation is distinguished from other forms of machine learning, image analysis, and statistical methods in that it utilizes a dynamical model of the system being analyzed.

En météorologie, l'assimilation de données est le procédé qui consiste à corriger, à l'aide d'observations, l'état de l'atmosphère d'une prévision météorologique.


Era.

The period of the Geonim began in 589 CE (Hebrew date: 4349), after the period of the Sevora'im, and ended in 1038 (Hebrew date: 4798). The first gaon of Sura, according to Sherira Gaon, was Mar Rab Mar, who assumed office in 609. The last gaon of Sura was Samuel ben Ḥofni, who died in 1034 CE; the last gaon of Pumbedita was Hezekiah Gaon, who was tortured to death by fanatics of the Buyid dynasty in 1040; hence the activity of the Geonim covers a period of nearly 450 years.  There were two major Geonic academies, one in Sura and the other in Pumbedita. The Sura academy was originally dominant, but its authority waned towards the end of the Geonic period and the Pumbedita Gaonate gained ascendancy (Louis Ginzberg in "Geonica").

Role in Jewish life.

The Geonim officiated, in the last place, as directors of the academies, continuing as such the educational activity of the Amoraim and Saboraim. For while the Amoraim, through their interpretation of the Mishnah, gave rise to the Talmud, and while the Saboraim definitively edited it, the Geonim's task was to interpret it; for them it became the subject of study and instruction, and they gave religio-legal decisions in agreement with its teachings.  During the geonic period the Babylonian schools were the chief centers of Jewish learning; the Geonim, the heads of these schools, were recognized as the highest authorities in Jewish law. Despite the difficulties which hampered the irregular communications of the period, Jews who lived even in most distant countries sent their inquiries concerning religion and law to these officials in Babylonia.  In the latter centuries of the geonic period, from the middle of the tenth to the middle of the eleventh, their supremacy lessened, as the study of the Talmud received care in other lands. The inhabitants of these regions gradually began to submit their questions to the heads of the schools in their own countries. Eventually they virtually ceased sending their questions to Babylonian Geonim.

The title "Gaon".

The title of gaon came to be applied to the heads of the two Babylonian academies of Sura and Pumbedita, though it did not displace the original title of "Rosh Yeshivah Ge'on Ya'akov" (Hebrew, head of the academy, pride of Jacob). The Aramaic term used was "Resh metivta."  The title "gaon" properly designated the office of head of the academy. The title became popular in use around the end of the 6th century. As the academies of Sura and Pumbedita were invested with judicial authority, the gaon officiated as supreme judge.  The organization of the Babylonian academies recalled the ancient Sanhedrin. In many responsa of the Geonim, members of the schools are mentioned who belonged to the "great sanhedrin", and others who belonged to the "small sanhedrin". In front of the presiding gaon and facing him were seated seventy members of the academy in seven rows of ten persons each, each person in the seat assigned to him, and the whole forming, with the gaon, the so-called "great sanhedrin". Gaon Amram calls them in a responsum the "ordained scholars who take the place of the great sanhedrin". (A regular ordination ("semichah") is of course not implied here: that did not exist in Babylonia, only a solemn nomination taking place.)  Gaon Ẓemaḥ refers in a responsum to "the ancient scholars of the first row, who take the place of the great sanhedrin". The seven masters, or "allufim" and the "ḥaberim", the three most prominent among the other members of the college, sat in the first of the seven rows. Nine sanhedrists were subordinated to each of the seven allufim, who probably supervised the instruction given during the entire year by their subordinates. The members of the academy who were not ordained sat behind the seven rows of sanhedrists.

Works of the Geonim.

Responsa.

Early in the Geonic era, the majority of the questions asked them were sent from Babylonia and the neighboring lands. Jewish communities in these regions had religious leaders who were somewhat acquainted with the Talmud, and who could on occasion visit the Jewish academies in Babylon. A literature of questions and answers developed, known as the responsa literature.  The questions were usually limited to one or more specific cases, while the responsum to such a query gave a ruling, a concise reason for it, together with supporting citations from the Talmud, and often a refutation of any possible objection.  More discursive were the responsa of the later geonim after the first half of the 9th century, when questions began to be sent from more distant regions, where the inhabitants were less familiar with the Talmud, and were less able to visit the Babylonian academies, then the only seats of Talmudic learning.  The later geonim did not restrict themselves to the Mishnah and Talmud, but used the decisions and responsa of their predecessors, whose sayings and traditions were generally regarded as authoritative. These responsa of the later geonim were often essays on Talmudic themes, and since a single letter often answered many questions, it frequently became book-length in size. Two important examples of such books are the Siddur of Amram Gaon, addressed to the Jews of Spain in response to a question about the laws of prayer, and the Epistle of Sherira Gaon, which sets out the history of the Mishnah and the Talmud in response to a question from Tunisia.  Some of the responsa that have survived are in their original form, while others are extant only as quotations in later works. Many have been found in the Cairo Genizah.  Examples of responsa collections are:

Other works.

Individual Geonim often composed treatises and commentaries. Three handbooks on Jewish law are:  The most notable author among the Geonim was Saadia Gaon, who wrote Biblical commentaries and many other works: he is best known for the philosophical work Emunoth ve-Deoth.

"Yarchei Kallah".

Two months of the year were denoted as "yarchei kallah", or "months of the bride" (referring to the Talmud) – the Hebrew months of Adar and Elul. During this time, foreign students assembled in the academy for common study.  During the first three weeks of the "yarchei kallah" the scholars seated in the first row reported on the Talmud treatise assigned for study during the preceding months; in the fourth week the other scholars and also some of the pupils were called upon. Discussions followed, and difficult passages were laid before the gaon, who also took a prominent part in the debates, and freely reproved any member of the college who was not up to the standard of scholarship. At the end of the "yarchei kallah" the gaon designated the Talmudic treatise which the members of the assembly were obliged to study in the months intervening until the next gathering took place. The students who were not given seats were exempt from this task, being free to choose a subject for study according to their needs.  During the "yarchei kallah", the gaon laid before the assembly a number of the questions that had been sent in during the year from all parts of the Diaspora. The requisite answers were discussed, and were finally recorded by the secretary of the academy according to the directions of the gaon. At the end of the "yarchei kallah" the questions, together with the answers, were read to the assembly, and the answers were signed by the gaon. A large number of the geonic responsa originated in this way; but many of them were written by the respective Geonim without consulting the kallah assemblies convened in the spring.

Individual Geonim.

Chananel Ben Chushiel (Rabbeinu Chananel) (990–1053) and Nissim Gaon (990–1062) of Kairouan, though not holders of the office of Gaon, are often ranked among the Geonim. Others, perhaps more logically, consider them as constituting the first generation of Rishonim. Maimonides (1135–1204) sometimes uses the term "Geonim" in an extended sense, to mean "leading authorities", regardless of what country they lived in.

References.

General collections of Geonic material, including but not limited to responsa:

Geonim (; ; also transliterated "Gaonim- singular Gaon") were the presidents of the two great Babylonian Talmudic Academies of Sura and Pumbedita, in the Abbasid Caliphate, and were the generally accepted spiritual leaders of the Jewish community worldwide in the early medieval era, in contrast to the "Resh Galuta" (Exilarch) who wielded secular authority over the Jews in Islamic lands.

Les Gueonim, Gaonim ou ghe'onim (hébreu: גאונים, sing. Gaon גאון) sont, au sens strict, les autorités juives halakhiques faisant suite aux Savoraïm (Sages qui avaient fixé le Talmud de Babylone), et "rashei yeshiva" (directeurs) des deux grandes académies talmudiques de Babylonie, Soura et Poumbedita. Le titre pourrait cependant avoir été antérieur, et fut revendiqué par les dirigeants de la Yeshiva en terre d'Israël.


Style.

Montaigne wrote in a rather crafted rhetoric designed to intrigue and involve the reader, sometimes appearing to move in a stream-of-thought from topic to topic and at other times employing a structured style that gives more emphasis to the didactic nature of his work. His arguments are often supported with quotations from Ancient Greek, Latin, and Italian texts such as "De rerum natura" by Lucretius and the works of Plutarch. Furthermore, his "Essays" were seen as an important contribution to both writing form and skepticism. The name itself comes from the French word "essais", meaning "attempts" or "tests", which shows how this new form of writing did not aim to educate or prove. Rather, his essays were exploratory journeys in which he works through logical steps to bring skepticism to what is being discussed.

Content.

Montaigne's stated goal in his book is to describe himself with utter frankness and honesty (""bonne foi""). The insight into human nature provided by his essays, for which they are so widely read, is merely a by-product of his introspection. Though the implications of his essays were profound and far-reaching, he did not intend, nor suspect his work to garner much attention outside of his inner circle, prefacing his essays with, "I am myself the matter of this book; you would be unreasonable to suspend your leisure on so frivolous and vain a subject."  Montaigne's essay topics spanned the entire spectrum of the profound to the trivial, with titles ranging from "Of Sadness and Sorrow" and "Of Conscience" to "Of Smells" and "Of Posting" (referring to posting letters). Montaigne wrote at a time preceded by Catholic and Protestant ideological tension. Christianity in the 15th and 16th centuries saw protestant authors consistently attempting to subvert Church doctrine with their own reason and scholarship. Consequently, Catholic scholars embraced skepticism as a means to discredit all reason and scholarship and accept Church doctrine through faith alone.  Montaigne never found certainty in any of his inquiries into the nature of man and things, despite his best efforts and many attempts. He mistrusted the certainty of both human reason and experience. He reasoned that while man is finite, truth is infinite; thus, human capacity is naturally inhibited in grasping reality in its fullness or with certainty. Though he did believe in the existence of absolute truth, he believed that such truth could only be arrived at by man through divine revelation, leaving us in the dark on most matters. He finds the great variety and volatility of human nature to be its most basic features, which resonates to the Renaissance thought about the fragility of humans. According to the scholar Paul Oskar Kristeller, "the writers of the period were keenly aware of the miseries and ills of our earthly existence". A representative quote is "I have never seen a greater monster or miracle than myself."  Citing the case of Martin Guerre as an example, Montaigne believes that humans cannot attain certainty. His philosophical skepticism is best expressed in the long essay "An Apology for Raymond Sebond" (Book 2, Chapter 12) in which he embraced the philosophy of Pyrrhonism. Montaigne posits that we cannot trust our reasoning because thoughts just occur to us: we don't truly control them. Further, he says we do not have good reasons to consider ourselves superior to the animals. He is highly skeptical of confessions obtained under torture, pointing out that such confessions can be made up by the suspect just to escape the torture he is subjected to. In the middle of the section normally entitled "Man's Knowledge Cannot Make Him Good," he wrote that his motto was "What do I know?". The essay on Sebond defended Christianity. Montaigne also eloquently employed many references and quotes from classical Greek and Roman, i.e. non-Christian authors, especially the atomist Lucretius.  Montaigne considered marriage necessary for the raising of children, but disliked the strong feelings of romantic love as being detrimental to freedom. One of his quotations is "Marriage is like a cage; one sees the birds outside desperate to get in, and those inside desperate to get out."  In education, he favored concrete examples and experience over the teaching of abstract knowledge that is expected to be accepted uncritically. Montaigne's essay "On the Education of Children" is dedicated to Diana of Foix.  He opposed European colonization of the Americas, deploring the suffering it brought upon the natives.

Chronology.

Montaigne heavily edited "Essays" at various points in his life. Sometimes he would insert just one word, while at other times he would insert whole passages. Many editions mark this with letters as follows:  A copy of the fifth edition of the "Essais" with Montaigne's own "C" additions in his own hand exists, preserved at the Municipal Library of Bordeaux (known to editors as the "Bordeaux Copy"). This edition gives modern editors a text dramatically indicative of Montaigne's final intentions (as opposed to the multitude of Renaissance works for which no autograph exists). Analyzing the differences and additions between editions show how Montaigne's thoughts evolved over time. Remarkably, he does not seem to remove previous writings, even when they conflict with his newer views.

Influence.

The remarkable modernity of thought apparent in Montaigne's essays, coupled with their sustained popularity, made them arguably the most prominent work in French philosophy until the Enlightenment. Their influence over French education and culture is still strong. The official portrait of former French president François Mitterrand pictured him facing the camera, holding an open copy of the "Essays" in his hands.  English journalist and politician J. M. Robertson argued that Montaigne's essays had a profound influence on the plays of William Shakespeare, citing their similarities in language, themes and structures.

The Essays (, ) of Michel de Montaigne are contained in three books and 107 chapters of varying length. They were originally written in Middle French and were originally published in the Kingdom of France. Montaigne's stated design in writing, publishing and revising the "Essays" over the period from approximately 1570 to 1592 was to record "some traits of my character and of my humours." The "Essays" were first published in 1580 and cover a wide range of topics.

Les "" sont l'œuvre majeure de Michel de Montaigne (1533-1592), à laquelle il consacre un labeur d'écriture et de réécriture à partir de 1572 continué pratiquement jusqu'à sa mort. Il traite de tous les sujets possibles, sans ordre apparent : médecine, amour et sexualité, livres, affaires domestiques, histoire ancienne, chevaux, maladie entre autres, auxquels Montaigne mêle des réflexions sur sa propre vie et sur l'Homme, le tout formant


In Descartes's writings.

Descartes first wrote the phrase in French in his 1637 "Discourse on the Method". He referred to it in Latin without explicitly stating the familiar form of the phrase in his 1641 "Meditations on First Philosophy". The earliest written record of the phrase in Latin is in his 1644 "Principles of Philosophy", where, in a margin note (see below), he provides a clear explanation of his intent: "[W]e cannot doubt of our existence while we doubt". Fuller forms of the phrase are attributable to other authors.

"Discourse on the Method".

The phrase first appeared (in French) in Descartes' 1637 "Discourse on the Method" in the first paragraph of its fourth part:

"Meditations on First Philosophy".

In 1641, Descartes published (in Latin) "Meditations on first philosophy" in which he referred to the proposition, though not explicitly as "cogito, ergo sum" in Meditation II:

"Principles of Philosophy".

In 1644, Descartes published (in Latin) his "Principles of Philosophy" where the phrase "ego cogito, ergo sum" appears in Part 1, article 7:  Descartes's margin note for the above paragraph is:

"The Search for Truth".

Descartes, in a lesser-known posthumously published work dated as written ca. 1647 and titled ("The Search for Truth by Natural Light"), wrote:

Other forms.

The proposition is sometimes given as. This fuller form was penned by the eloquent French literary critic, Antoine Léonard Thomas, in an award-winning 1765 essay in praise of Descartes, where it appeared as "" ('Since I doubt, I think; since I think, I exist'). With rearrangement and compaction, the passage translates to "I doubt, therefore I think, therefore I am," or in Latin, ""dubito, ergo cogito, ergo sum"."  A further expansion, ("...—a thinking thing") extends the "cogito" with Descartes's statement in the subsequent "Meditation", ("I am a thinking [conscious] thing, that is, a being who doubts, affirms, denies, knows a few objects, and is ignorant of many..."). This has been referred to as "the expanded "cogito"."

Translation.

Neither nor indicate whether the verb form corresponds to the English simple present or progressive aspect. Translation needs a larger context to determine aspect.  Following John Lyons (1982), Vladimir Žegarac notes, "The temptation to use the simple present is said to arise from the lack of progressive forms in Latin and French, and from a misinterpretation of the meaning of "cogito" as habitual or generic" (cf. gnomic aspect). Also following Lyons, Ann Banfield writes, "In order for the statement on which Descartes's argument depends to represent certain knowledge,... its tense must be a true present—in English, a progressive,... not as 'I think' but as 'I am thinking, in conformity with the general translation of the Latin or French present tense in such nongeneric, nonstative contexts." Or in the words of Simon Blackburn, "Descartes’s premise is not ‘I think’ in the sense of ‘I ski’, which can be true even if you are not at the moment skiing. It is supposed to be parallel to ‘I am skiing’."  Fumitaka Suzuki (2012) writes "Taking consideration of Cartesian theory of continuous creation, which theory was developed especially in the Meditations and in the Principles, we would assure that 'I am thinking, therefore I am/exist' is the most appropriate English translation of 'ego cogito, ergo sum'."  The similar translation “I am thinking, therefore I exist” of Descartes's correspondence in French (“, ”) appears in "The Philosophical Writings of Descartes" by Cottingham et al. (1988).  The earliest known translation as "I am thinking, therefore I am" is from 1872 by Charles Porterfield Krauth.

Interpretation.

As put succinctly by Krauth (1872), "That cannot doubt which does not think, and that cannot think which does not exist. I doubt, I think, I exist."  The phrase "cogito, ergo sum" is not used in Descartes's "Meditations on First Philosophy" but the term "the "cogito"" is used to refer to an argument from it. In the "Meditations", Descartes phrases the conclusion of the argument as "that the proposition, "I am, I exist," is necessarily true whenever it is put forward by me or conceived in my mind" ("Meditation" II).  At the beginning of the second meditation, having reached what he considers to be the ultimate level of doubt—his argument from the existence of a deceiving god—Descartes examines his beliefs to see if any have survived the doubt. In his belief in his own existence, he finds that it is impossible to doubt that he exists. Even if there were a deceiving god (or an evil demon), one's belief in their own existence would be secure, for there is no way one could be deceived unless one existed in order to be deceived.  But I have convinced myself that there is absolutely nothing in the world, no sky, no earth, no minds, no bodies. Does it now follow that I, too, do not exist? No. If I convinced myself of something [or thought anything at all], then I certainly existed. But there is a deceiver of supreme power and cunning who deliberately and constantly deceives me. In that case, I, too, undoubtedly exist, if he deceives me; and let him deceive me as much as he can, he will never bring it about that I am nothing, so long as I think that I am something. So, after considering everything very thoroughly, I must finally conclude that the proposition, "I am, I exist," is necessarily true whenever it is put forward by me or conceived in my mind. (AT VII 25; CSM II 16–17)  There are three important notes to keep in mind here. First, he claims only the certainty of "his own" existence from the first-person point of view — he has not proved the existence of other minds at this point. This is something that has to be thought through by each of us for ourselves, as we follow the course of the meditations. Second, he does not say that his existence is necessary; he says that "if he thinks", then necessarily he exists (see the instantiation principle). Third, this proposition "I am, I exist" is held true not based on a deduction (as mentioned above) or on empirical induction but on the clarity and self-evidence of the proposition. Descartes does not use this first certainty, the "cogito", as a foundation upon which to build further knowledge; rather, it is the firm ground upon which he can stand as he works to discover further truths. As he puts it:  Archimedes used to demand just one firm and immovable point in order to shift the entire earth; so I too can hope for great things if I manage to find just one thing, however slight, that is certain and unshakable. (AT VII 24; CSM II 16)  According to many Descartes specialists, including Étienne Gilson, the goal of Descartes in establishing this first truth is to demonstrate the capacity of his criterion — the immediate clarity and distinctiveness of self-evident propositions — to establish true and justified propositions despite having adopted a method of generalized doubt. As a consequence of this demonstration, Descartes considers science and mathematics to be justified to the extent that their proposals are established on a similarly immediate clarity, distinctiveness, and self-evidence that presents itself to the mind. The originality of Descartes's thinking, therefore, is not so much in expressing the "cogito"—a feat accomplished by other predecessors, as we shall see—but on using the "cogito" as demonstrating the most fundamental epistemological principle, that science and mathematics are justified by relying on clarity, distinctiveness, and self-evidence. Baruch Spinoza in ""Principia philosophiae cartesianae"" at its "Prolegomenon" identified "cogito ergo sum" the ""ego sum cogitans"" (I am a thinking being) as the thinking substance with his ontological interpretation.

Predecessors.

Although the idea expressed in "cogito, ergo sum" is widely attributed to Descartes, he was not the first to mention it. Plato spoke about the "knowledge of knowledge" (Greek: νόησις νοήσεως, "nóesis noéseos") and Aristotle explains the idea in full length: But if life itself is good and pleasant...and if one who sees is conscious that he sees, one who hears that he hears, one who walks that he walks and similarly for all the other human activities there is a faculty that is conscious of their exercise, so that whenever we perceive, we are conscious that we perceive, and whenever we think, we are conscious that we think, and to be conscious that we are perceiving or thinking is to be conscious that we exist... ("Nicomachean Ethics", 1170a25 ff.)  In the late sixth or early fifth century BC, Parmenides is quoted as saying "For to be aware and to be are the same" (B3). Augustine of Hippo in "De Civitate Dei" (book XI, 26) writes "If I am mistaken, I am" ("Si...fallor, sum"), and also anticipates modern refutations of the concept. Furthermore, in the "Enchiridion" (ch. 7, sec. 20), Augustine attempts to refute skepticism by stating, "[B]y not positively affirming that they are alive, the skeptics ward off the appearance of error in themselves, yet they do make errors simply by showing themselves alive; one cannot err who is not alive. That we live is therefore not only true, but it is altogether certain as well." In 1640 correspondence, Descartes thanked two colleagues for drawing his attention to Augustine and notes similarity and difference. (See CSMK III 159, 161.)  Another predecessor was Avicenna's "Floating Man" thought experiment on human self-awareness and self-consciousness.  The 8th century Hindu philosopher Adi Shankara wrote, in a similar fashion, that no one thinks 'I am not', arguing that one's existence cannot be doubted, as there must be someone there to doubt. The central idea of "cogito, ergo sum" is also the topic of "Mandukya Upanishad".  Spanish philosopher Gómez Pereira in his 1554 work "De Inmortalitate Animae", published in 1749, wrote ""nosco me aliquid noscere, & quidquid noscit, est, ergo ego sum"" ('I know that I know something, anyone who knows exists, then I exist').

Critique.

Use of "I".

In "Descartes, The Project of Pure Enquiry", Bernard Williams provides a history and full evaluation of this issue. The first to raise the "I" problem was Pierre Gassendi. He "points out that recognition that one has a set of thoughts does not imply that one is a particular thinker or another. Were we to move from the observation that there is thinking occurring to the attribution of this thinking to a particular agent, we would simply assume what we set out to prove, namely, that there exists a particular person endowed with the capacity for thought." In other words, "the only claim that is indubitable here is the agent-independent claim that there is cognitive activity present."  The objection, as presented by Georg Lichtenberg, is that rather than supposing an entity that is thinking, Descartes should have said: "thinking is occurring." That is, whatever the force of the "cogito", Descartes draws too much from it; the existence of a thinking thing, the reference of the "I," is more than the "cogito" can justify. Friedrich Nietzsche criticized the phrase in that it presupposes that there is an "I", that there is such an activity as "thinking", and that "I" know what "thinking" is. He suggested a more appropriate phrase would be "it thinks" wherein the "it" could be an impersonal subject as in the sentence "It is raining."

Kierkegaard.

The Danish philosopher Søren Kierkegaard calls the phrase a tautology in his "Concluding Unscientific Postscript". He argues that the "cogito" already presupposes the existence of "I", and therefore concluding with existence is logically trivial. Kierkegaard's argument can be made clearer if one extracts the premise "I think" into the premises "'x' thinks" and "I am that 'x'", where "x" is used as a placeholder in order to disambiguate the "I" from the thinking thing.  Here, the "cogito" has already assumed the "I"'s existence as that which thinks. For Kierkegaard, Descartes is merely "developing the content of a concept", namely that the "I", which already exists, thinks. As Kierkegaard argues, the proper logical flow of argument is that existence is already assumed or presupposed in order for thinking to occur, not that existence is concluded from that thinking.

Williams.

Bernard Williams claims that what we are dealing with when we talk of thought, or when we say "I am thinking," is something conceivable from a third-person perspective; namely objective "thought-events" in the former case, and an objective thinker in the latter. He argues, first, that it is impossible to make sense of "there is thinking" without relativizing it to "something." However, this something cannot be Cartesian egos, because it is impossible to differentiate objectively between things just on the basis of the pure content of consciousness. The obvious problem is that, through introspection, or our experience of consciousness, we have no way of moving to conclude the existence of any third-personal fact, to conceive of which would require something above and beyond just the purely subjective contents of the mind.

Heidegger.

As a critic of Cartesian subjectivity, Heidegger sought to ground human subjectivity in death as that certainty which individualizes and authenticates our being. As he wrote in 1927:This certainty, that "I myself am in that I will die," is the basic certainty of Dasein itself. It is a genuine statement of Dasein, while "cogito sum" is only the semblance of such a statement. If such pointed formulations mean anything at all, then the appropriate statement pertaining to Dasein in its being would have to be "sum moribundus" [I am in dying], "moribundus" not as someone gravely ill or wounded, but insofar as I am, I am "moribundus". The "MORIBUNDUS" first gives the "SUM" its sense.

John Macmurray.

The Scottish philosopher John Macmurray rejects the "cogito" outright in order to place action at the center of a philosophical system he entitles the Form of the Personal. "We must reject this, both as standpoint and as method. If this be philosophy, then philosophy is a bubble floating in an atmosphere of unreality." The reliance on thought creates an irreconcilable dualism between thought and action in which the unity of experience is lost, thus dissolving the integrity of our selves, and destroying any connection with reality. In order to formulate a more adequate "cogito", Macmurray proposes the substitution of "I do" for "I think," ultimately leading to a belief in God as an agent to whom all persons stand in relation.

This proposition became a fundamental element of Western philosophy, as it purported to form a secure foundation for knowledge in the face of radical doubt. While other knowledge could be a figment of imagination, deception, or mistake, Descartes asserted that the very act of doubting one's own existence served—at minimum—as proof of the reality of one's own mind; there must be a thinking entity—in this case the self—for there to be a thought.

Dans le vocabulaire philosophique, l'expression est fréquemment raccourcie et substantivée. On parle simplement "du "cogito, pour exprimer l'intuition acquise par le sujet grâce à sa conscience de lui-même. Le cogito est alors pris comme une découverte qui n'est plus toujours liée à Descartes lui-même. On parle ainsi de cogito augustinien, avant Descartes, ou de cogito husserlien, après lui.


Early life.

Carola Maria Häggkvist was born on 8 September 1966 at Södersjukhuset in Stockholm. She grew up in Norsborg, south of the Swedish capital. At the age of eight, she began to perform at Stockholm's Miniteatern; she also attended Adolf Fredrik's Music School. In 1977, Häggkvist won a talent competition and appeared on television for the first time, on "Sveriges magasin", performing "Krokodilbarnets klagan".

Career.

1981–1989: Early career and "Främling".

In 1981, Swedish music promoter Bert Karlsson met Häggkvist after she performed on the television series "Hylands hörna" and offered her the chance to take part in "Melodifestivalen", the Swedish selection for the Eurovision Song Contest in 1982. She turned down the offer. Songwriter Lasse Holm offered Häggkvist two of his songs for Melodifestivalen 1983, "Mona Lisa" and "Främling". "Främling" was chosen, and with it Häggkvist won the right to represent Sweden at that year's Eurovision Song Contest in Munich. The song scored eight points, the highest possible mark, from all eleven juries. Häggkvist represented Sweden at the Eurovision Song Contest on 23 April. She finished third in front of 6.1 million Swedish television viewers, 84% of the country's population. This is still a record in Sweden.  "Främling" became the title track to Häggkvist's debut album, which sold over one million copies, making it the biggest-selling album in Swedish history. After Eurovision, Häggkvist embarked on a tour of European television programmes, promoting "Främling" and performing in it several languages: in English as "Love Isn't Love", in German as "Fremder", and in Dutch as "Je ogen hebben geen geheimen". The album contained hits like "Mickey", "Liv", "Gloria" and "Tokyo". In December 1983, she released her first Christmas album, "Julefrid med Carola", which sold 200,000 copies. In 1984, Häggkvist released two top-selling pop/rock albums that together sold over 1 million copies. "Tommy tycker om mig" became a huge hit in Sweden, together with "Hunger". She later travelled to Japan and recorded a single in Japanese. In 1985, the Bee Gees collaborated with her on the album "Runaway", which was written by the Gibb brothers and produced by Maurice Gibb. The record sold double platinum when released in Sweden the following year. "The Runaway", "Brand New Heart", "Spread your wings" and "Radiate" became massive hits in Scandinavia. In 1987, Häggkvist embarked on a church tour with pianist Per-Erik Hallin. After this followed a career hiatus for the singer.

1990–1991: New image, independence, and Eurovision victory.

In 1990, she returned to Melodifestivalen, with "Mitt i ett äventyr" (In the middle of an adventure). The song finished second in the festival, failing to earn Häggkvist the right to represent Sweden at Eurovision. Edin-Ådahl won the event. Her comeback album, titled "Much More", was released, earning a gold certificate in Sweden. However, Häggkvist and songwriter Stephan Berg had already begun planning another attempt at Eurovision.  In 1991, she returned to Melodifestivalen with "Fångad av en stormvind" (Captured by a lovestorm). The song won the festival by thirty-two points and became the Swedish entry for the Eurovision Song Contest in Rome. British bookmakers considered Häggkvist second favourite to win the contest. On the night of the contest, with one voting jury left to announce their scores, three countries remained in contention to win the contest: Sweden, with 146 points; Israel, with 139; and France, with 134. Neither Israel nor Sweden won any points from the Italian jury, but France won twelve, leaving Sweden and France tied for first place with 146 at the conclusion of the voting. Sweden won the contest after a recount, having received five ten-point scores during the voting versus France's two. "Fångad av en stormvind" became a huge hit in Europe, and was followed by a compilation album, "Hits", and a Christmas album, "Jul". After her victory, she released an international version of "Much More" and went on an extended promotional tour throughout Europe. Her album produced several hits, among them "I'll live" and "All the Reasons to Live".

1992–2004: Albums, tours, and musicals.

Häggkvist was the first Scandinavian pop artist to perform in China—in front of an estimated 600 million television viewers; she also released an album in China in 1992. In 1992 and 1993, Rival International, released Carola's earlier albums on CD. She was originally signed to Mariann Records in Scandinavia.  After the tenth anniversary of her breakthrough in 1993, she recorded a gospel album, "My Tribute", which was released in sixteen countries, making her gospel artist of the year in the Netherlands in 1994. The album contains the hit-single "My Tribute", one of Häggkvist's best-known songs. In 1994, Häggkvist released a rock-themed album, '"Personligt" (Personally), marking her debut as a songwriter and selling gold. "Så länge jag lever", "Sanna Vänner" and "Guld i dina ögon" became hits and received a great amount of radio airplay.  In 1995, Häggkvist made her debut as a musical actress, playing Maria in "The Sound of Music" opposite Tommy Körberg as the male lead. She played the role in 325 performances and won the prestigious "Guldmasken" (Golden Mask) award. Three years later, she sang the theme song in the Norwegian musical "Sophie's World", which was released on the album "Songs from Sophie's World". Also in 1998, Häggkvist played the voice of Mirjam in the Swedish version of "The Prince of Egypt". In 2002, she made a short appearance as Fantine in "Les Misérables" in London and five Scandinavian cities.  In November 1997, Häggkvist released another compilation album, "De bästa av Carola" ("The Best of Carola"), and with it several new singles like "Dreamer". Following this came an album of tracks penned by Lina Sandell, "Blott en dag" ("Just One Day"). The album received excellent reviews and revealed Carola's passion for hymns. In 1999, another Christmas album was released: "Jul i Betlehem" ("Christmas in Bethlehem"). The album sold 600,000 units throughout Scandinavia, including 350,000 in Sweden. and became the biggest-selling album of 1999. She also co-wrote the ballad "Himlen i min famn", which remains a popular Christmas song that is often performed at Christmas concerts. In the summer of 1999, she toured in the "Rhapsody in Rock".  In 2001, she released "Sov på min arm", an album based on Christian hymns, gospel melodies and intimate ballads. It became one of the most-sold albums in Scandinavia that year. In 2002, she release the pop/country album "My Show", which received great reviews. The album, which marked Häggkvist's return to the pop scene, contained several hits such as "The Light", "I believe in love", which also topped the Estonian and Brazilian charts, and "A Kiss Goodbye". Even though the album only peaked at number 6 on the Swedish album chart, it sold 100,000 copies by the end of the year. In the summer, Häggkvist embarked on a huge and luxurious Scandinavian tour.  In 2003, Häggkvist submitted a song, "Autumn Leaf", for Melodifestivalen 2003. Having performed the demo, she was required to perform the song when it qualified for the competition. Häggkvist decided against doing that, and the song was disqualified from the competition. "Autumn Leaf" appeared on Häggkvist's next album, "Guld, platina & passion", in Swedish as "När löven faller" (When the leaves fall). The ballad became an enormous hit. "Guld, platina & passion" reached number 1 on the Swedish charts and sold over 300,000 copies. She also recorded her favorite Elvis Presley songs, "Walk a mile in my shoes" and "If I can dream". The following year, Häggkvist released a religious album, "Credo", which she described as "an expression of my love for God". The album peaked at spot 2 on the Swedish album chart. This was followed by "Störst av allt", which Dan Backman of "Svenska Dagbladet" wrote featured "spiritually aimed music...revolving around belonging, love, death and eternity". "Genom Allt" became a huge radio hit in Sweden and the soul ballad "Allt kommer bli bra mamma", a dedication to her deceased mother, became popular at religious events.

2005–present: Return to Eurovision.

Having performed as part of the interval act at Melodifestivalen 2005, Häggkvist confirmed that she would return to the competition in 2006. She performed "Evighet" ("Eternity"), written by Bobby Ljunggren, Henrik Wikström and, which she described as a "true winning song". The song qualified from the semi-final in Gothenburg on 11 March 2006, and was widely tipped to win the festival outright as the final at the Stockholm Globe Arena approached. Despite finishing second with the regional juries to Andreas Johnson, "Evighet" won the competition with 232 points. Prior to the contest, Carola visited 12 countries where she promoted her song. "Invincible" received a large amount of air play on the radios in these countries. The song qualified from the semi-final of the Eurovision Song Contest in Athens, in English as "Invincible". Häggkvist in the end finished fifth out of twenty-four with 170 points. This placing also made her the second-most artist in the history of Eurovision, counting by total points earned in her performances, with her three songs scoring a total of 442 points, behind only Dima Bilan, the 2006 runner-up and 2008 winner.  Following Melodifestivalen, Häggkvist released a pop album, "Från nu till evighet" ("From Now to Eternity"). Lennart Wrigholm reviewed the album for "Musiklandet"; he criticised the amount of new material on the album: "Has this old lady really got such a workload that she cannot put more than ten new tracks on her album?" and wrote that the inclusion of the English version of "Evighet" as a bonus track was "an insult to the potential buyer". On the other hand, "Expressen"s Anders Nunstedt wrote that on "Jag ger allt" ("I Give It All") "the title does not lie" and that "Vem kan älska mig" ("Who Can Love Me") features a "brilliant refrain". The album topped the Swedish sales chart, and sold approximately 100,000 copies by the end of the year. "Stanna eller gå", a Latin-inspired pop song, became a radio hit during the summer. Following the album's release, Häggkvist toured Sweden and received outstanding reviews. During the autumn, Häggkvist had problems with her voice but nonetheless sang "Because We Believe", a song written by Andrea Bocelli, with the Italian tenor.  In late 2007, Häggkvist released another Christmas album, "I denna natt blir världen ny" ("There is a New World This Night"), a sequel to "Jul i Betlehem". The album featured songs in Swedish and English, and was recorded in Jerusalem in June 2007. Stefan Malmqvist of "Svenska Dagbladet" wrote that, as in previous Christmas albums, Häggkvist is "a saccharine version of herself" when singing Christmas carols. The album was reported to have sold 90,000 copies. Included on the album was the gospel song "Go and Tell It on the Mountain". After the release she toured Scandinavia.  Carola entered Melodifestivalen 2008 as part of the duo "Johnson & Häggkvist" with Andreas Johnson. Their first single was called "Lucky Star" which became popular on the radio. In the melodifestival in February, they sang "One Love", written by Carola, Johnson and Peter Kvint. They were the early favourites to win the whole show, taking part in the second qualifier. They qualified for the Second Chance round, missing out on an automatic final spot. Though widely tipped to qualify for the final after all, they did not even proceed from the first voting round in the Second Chance programme. Although "One Love" did not become an enormous success, the song "Lucky Star" which they released a few months prior to the contest did sell well, and topped the Swedish charts for weeks. Carola decided to take it easy the rest of the year, but did embark on a small Christmas tour at the end of the year. In 2009, Carola was reportedly working on her upcoming album, and other projects. She went to the United States to record some new material. She departed from her recording company and signed a contract with X5 Music Group, in which she aims to transfer her music abroad through the internet. In June, she hosted "Carola Camp", a camp designed to help talented young singers and entertainers. In May, she performed at the Eurovision Song Contest held in Moscow at the kick-off ceremony, performing her 3 Eurovision songs. In July, she performed, together with the Eurovision winner Alexander Rybak in Norway and sang "Fairytale" and "Främling" and The Jackson 5's "I'll Be There". At the end of 2009, she released the album "Christmas in Bethlehem", which contained duets with artists like Paul Potts. She embarked on yet another Christmas tour, visiting Sweden, Norway, Denmark and Finland. She also launched her new website.  Carola attended in the final of the Eurovision Song Contest 2013 in Malmö and performed in a humorous interval act about Swedish culture.  In the summer of 2010, Carola embarked on tour across Sweden, singing the hits of both Elvis Presley and Barbra Streisand. The influence came from Carola's childhood, where her father and her mother would play records by both their favourite artists. The tour was an instant success, selling out and becoming one of the few tours to sell out that year. She took time out from the tour to appear on Allsång på Skansen, and in March 2011 she released a studio album, containing twelve songs.  In 2014 Häggkvist participated in "Så mycket bättre" on TV4.  Carola attended the final of the Eurovision Song Contest 2016 in Stockholm and was briefly interviewed on screen along with another previous Swedish winner Loreen.  In late-October 2016, she released her new Christmas album titled "Drömmen om julen". The release was followed by a tour.

Personal life and media attention.

Her status as one of the most popular national celebrities of her country made her more or less constantly followed by the tabloid press. She has often talked about her Christian faith and much of the focus has been around her membership in the controversial evangelical church "Livets Ord" (Word of Life).  She was married to Runar Søgaard, a Norwegian Christian preacher, with whom she has a son, Amadeus, and a daughter, Zoe, who was adopted from South Africa in 2012. (Her parents had both died in 2004.)

Controversy regarding opinions on homosexuality.

In an interview in 2002 for the Swedish gay magazine "QX", she alienated many gays and some heterosexual fans by alleging that she knew homosexual people who had become heterosexual through prayers. She also said that homosexuality would always remain "unnatural" to her.  Four years later, her comment was brought up when she participated in the Swedish national selection for the Eurovision Song Contest in March 2006. During a press conference a journalist tried to ask her about her opinions on homosexuality, but she did not answer.  On 15 March 2006 Rickard Engfors, who was Carola's cooperating partner during the Melodifestivalen and Eurovision Song Contest 2006, said "Carola doesn't hate gays. If she did, I wouldn't work for her. She is a fantastic person."  During an exclusive interview for one of the Eurovision-related websites before the 2006 contest, Carola was also questioned about this, and she stated that she "would love for every gay person to feel that she loves them" and that she does not think that "being gay is a sickness". She went on to criticize the tabloids for misinterpreting her original words and making an issue out of it. Later in the interview, she also commented on one of her supporting dancers being gay and his boyfriend being "great".  In 2008, she spoke to the newspaper "Aftonbladet" and again revisited her opinions about homosexuality, which she insisted have evolved over the past two decades and are very inclusive. She said, "I actually invited gays from "QX" to my 25-year anniversary [concert], but "QX" turned it down. What can I do? I love all people. I love the gays. So I am definitely not homophobic in any way. We are here for the music and I have no wacky opinions. And I feel love from many homosexuals too."

Carola Maria Häggkvist (; born 8 September 1966), also known as simply Carola, is a Swedish singer and songwriter. She has been among Sweden's most popular performers since the early 1980s, and has released albums ranging from pop and disco to hymns and folk music. Her debut album, "Främling" (1983), sold around one million copies and remains the biggest-selling album in Swedish music history. She has also worked as a songwriter. During her career, she has recorded many top-selling albums and singles and is referred to as Sweden's most prominent female singer. Some of her biggest hits are "Främling", "Tommy tycker om mig", "Fångad av en stormvind", "All the Reasons to Live", "I Believe in Love", "Genom allt", and "Evighet". She has released records in various languages: Swedish, Dutch, German, English, Norwegian and Japanese.

Carola Häggkvist, plus connue sous le simple nom de Carola, au civil "Carola Maria Söörgaard Häggkvist", (née le à Hägersten, Stockholm, Suède), est une chanteuse suédoise ayant remporté l'Eurovision 1991.


History.

Exclusively a palace guard, the Noble Guard saw no active military service or combat during the several military campaigns that engaged the Papal States between 1801 and 1870. With the unification of Italy and the abolition of the Papal States in 1870, the Noble Guard restricted its activity to the buildings and grounds of the Vatican. Though nominally still a cavalry unit, the unit had little opportunity to deploy on horseback in the limited confines of the Vatican, although two mounted troopers would accompany the papal carriage when the Pope was driven around the Vatican gardens. In 1904 mounted service was abolished entirely and the last horses were sold off. Originally armed with carbines, pistols and sabers, after 1870 the guardsmen carried only a saber.  The corps was always a volunteer one - its members were not paid for their service, although they received an allowance for their uniforms. Recruits were drawn from noble families in Rome, although in the twentieth century requirements were relaxed in practice to allow nobility from other regions of Italy to join the corps. The commander of the corps was called the Captain. One of the subordinate positions within the corps was that of Hereditary Standard-Bearer, who was responsible for carrying the standard of the Catholic Church.  After 1870, the Noble Guard, now reduced to a force of fewer than 70 men, performed mainly ceremonial duties as an honour guard. Guardsmen most commonly appeared in public when the pope presided over ceremonies in Saint Peter's Basilica. When the pope was carried in the "sedia gestatoria", Noble Guards walked alongside the papal chair. During the hours reserved for papal audiences, guardsmen also stood in the antechamber of the papal apartments and, on formal occasions, on either side of the papal throne. During the Second World War, the Noble Guard shared responsibility with the Swiss Guard for the personal security of Pope Pius XII. For the first time since 1870 pistols were issued to duty personnel. Throughout the war, Noble Guards mounted guard outside the papal apartment night and day and guardsmen followed Pius XII when he took his daily walks in the Vatican Gardens.

Abolition.

The Noble Guard was abolished by Pope Paul VI in 1970 as part of the reforms of the Church following Vatican II. The elitist image of a privileged ceremonial corps was considered to be out of sympathy with a simpler and more inclusive era. A planned farewell audience for the guardsmen with the Pope did not take place and the property of the unit was requisitioned at short notice by the Papal Secretariat of State. Former members of the Noble Guard have a veterans' association, "La Compagnia delle Lance Spezzate" (The Company of the Broken Lances).

The Noble Guard () was one of the household guard units serving the Pope, and formed part of the military in Vatican City. It was formed by Pope Pius VII in 1801 as a regiment of heavy cavalry. Conceived as the Pope's personal guard, the unit provided a mounted escort for the Pope when he moved about Rome in his carriage and mounted guard outside his apartments in the papal palaces. The guardsmen were also available for special missions within the Papal States at the behest of the pope. One of their first major duties was to escort Pius VII to Paris for the Coronation of Napoleon I in 1804.

La garde noble est un ancien corps militaire chargé de la protection et de la garde d'honneur du pape. Elle est créée par Pie VII le et tire son nom d'une institution similaire de la cour d'Espagne. Cette unité ne recrute que dans les rangs de la noblesse des États pontificaux : les candidats doivent fournir des preuves de noblesse. Ses soldats sont postés comme gardes du palais du Vatican et escortent le pape dans ses déplacements. Ils accompagnent également les représentants du pape portant la rose d'or, ou encore la barrette à un néo-cardinal.