Rationality

Rationality is the quality or state of being rational – that is, being based on or agreeable to reason. Rationality implies the conformity of one's beliefs with one's reasons to believe, and of one's actions with one's reasons for action. "Rationality" has different specialized meanings in philosophy, economics, sociology, psychology, evolutionary biology, game theory and political science.
Theories of rational thinking.
Max Weber.
The German scholar Max Weber proposed an interpretation of social action that distinguished between four different idealized types of rationality.
The first, which he called "Zweckrational" or purposive/instrumental rationality, is related to the expectations about the behavior of other human beings or objects in the environment. These expectations serve as means for a particular actor to attain ends, ends which Weber noted were "rationally pursued and calculated." The second type, Weber called "Wertrational" or value/belief-oriented. Here the action is undertaken for what one might call reasons intrinsic to the actor: some ethical, aesthetic, religious or other motives, independent of whether it will lead to success. The third type was affectual, determined by an actor's specific affect, feeling, or emotion—to which Weber himself said that this was a kind of rationality that was on the borderline of what he considered "meaningfully oriented." The fourth was traditional or conventional, determined by ingrained habituation. Weber emphasized that it was very unusual to find only one of these orientations: combinations were the norm. His usage also makes clear that he considered the first two as more significant than the others, and it is arguable that the third and fourth are subtypes of the first two.
The advantage in Weber's interpretation of rationality is that it avoids a value-laden assessment, say, that certain kinds of beliefs are irrational. Instead, Weber suggests that ground or motive can be given—for religious or affect reasons, for example—that may meet the criterion of explanation or justification even if it is not an explanation that fits the "Zweckrational" orientation of means and ends. The opposite is therefore also true: some means-ends explanations will not satisfy those whose grounds for action are "Wertrational".
Weber's constructions of rationality have been critiqued both from a Habermasian (1984) perspective (as devoid of social context and under-theorised in terms of social power) and also from a feminist perspective (Eagleton, 2003) whereby Weber's rationality constructs are viewed as imbued with masculine values and oriented toward the maintenance of male power. An alternative position on rationality (which includes both bounded rationality, as well as the affective and value-based arguments of Weber) can be found in the critique of Etzioni (1988), who reframes thought on decision-making to argue for a reversal of the position put forward by Weber. Etzioni illustrates how purposive/instrumental reasoning is subordinated by normative considerations (ideas on how people 'ought' to behave) and affective considerations (as a support system for the development of human relationships).
Psychology.
In the psychology of reasoning, psychologists and cognitive scientists have defended different positions on human rationality. One prominent view, due to Philip Johnson-Laird and Ruth M. J. Byrne among others is that humans are rational in principle but they err in practice, that is, humans have the competence to be rational but their performance is limited by various factors. However, it has been argued that many standard tests of reasoning, such as those on the conjunction fallacy, on the Wason selection task, or the base rate fallacy suffer from methodological and conceptual problems. This has led to disputes in psychology over whether researchers should (only) use standard rules of logic, probability theory and statistics, or rational choice theory as norms of good reasoning. Opponents of this view, such as Gerd Gigerenzer, favor a conception of bounded rationality, especially for tasks under high uncertainty.
Richard Brandt.
Richard Brandt proposed a "reforming definition" of rationality, arguing someone is rational if their notions survive a form of cognitive-psychotherapy.
Robert Audi.
Robert Audi developed a comprehensive account of rationality that covers both the theoretical and the practical side of rationality. This account centers on the notion of a "ground": a mental state is rational if it is "well-grounded" in a source of justification. Irrational mental states, on the other hand, lack a sufficient ground. For example, the perceptual experience of a tree when looking outside the window can ground the rationality of the belief that there is a tree outside. 
Audi is committed to a form of foundationalism: the idea that justified beliefs, or in his case, rational states in general, can be divided into two groups: the "foundation" and the "superstructure". The mental states in the superstructure receive their justification from other rational mental states while the foundational mental states receive their justification from a more basic source. For example, the above-mentioned belief that there is a tree outside is foundational since it is based on a basic source: perception. Knowing that trees grow in soil, we may deduce that there is soil outside. This belief is equally rational, being supported by an adequate ground, but it belongs to the superstructure since its rationality is grounded in the rationality of another belief. Desires, like beliefs, form a hierarchy: intrinsic desires are at the foundation while instrumental desires belong to the superstructure. In order to link the instrumental desire to the intrinsic desire an extra element is needed: a belief that the fulfillment of the instrumental desire is a means to the fulfillment of the intrinsic desire.
Audi asserts that all the basic sources providing justification for the foundational mental states come from experience. As for "beliefs", there are four types of experience that act as sources: perception, memory, introspection, and rational intuition. The main basic source of the rationality of "desires", on the other hand, comes in the form of hedonic experience: the experience of pleasure and pain. So, for example, a desire to eat ice-cream is rational if it is based on experiences in which the agent enjoyed the taste of ice-cream, and irrational if it lacks such a support. Because of its dependence on experience, rationality can be defined as a kind of responsiveness to experience.
"Actions", in contrast to beliefs and desires, don't have a source of justification of their own. Their rationality is grounded in the rationality of other states instead: in the rationality of beliefs and desires. Desires motivate actions. Beliefs are needed here, as in the case of instrumental desires, to bridge a gap and link two elements. Audi distinguishes the "focal" rationality of individual mental states from the "global" rationality of "persons". Global rationality has a derivative status: it depends on the focal rationality. Or more precisely: "Global rationality is reached when a person has a sufficiently integrated system of sufficiently well-grounded propositional attitudes, emotions, and actions". Rationality is "relative" in the sense that it depends on the experience of the person in question. Since different people undergo different experiences, what is rational to believe for one person may be irrational to believe for another person. That a belief is rational doesn't entail that it is "true".
Disputes about the concept of rationality.
Meaning.
Abulof argues that rationality has become an "essentially contested concept," as its "proper use… inevitably involves endless disputes." He identifies "four fronts" for the disputes about the meaning of rationality: 
Relativity.
To determine what behavior is the most rational, one needs to make several key assumptions, and also needs a logical formulation of the problem. When the goal or problem involves making a decision, rationality factors in all information that is available (e.g. complete or incomplete knowledge). Collectively, the formulation and background assumptions are the models within which rationality applies. Rationality is relative according to some philosophers: if one accepts a model in which benefiting oneself is optimal, then rationality is equated with behavior that is self-interested to the point of being selfish; whereas if one accepts a model in which benefiting the group is optimal, then purely selfish behavior is deemed irrational. It is thus meaningless, seen from this point of view, to assert rationality without also specifying the background model assumptions describing how the problem is framed and formulated.
Emotions.
It is believed by some philosophers (notably A. C. Grayling) that a good rationale must be independent of emotions, personal feelings or any kind of instincts. Any process of evaluation or analysis, that may be called rational, is expected to be highly objective, logical and "mechanical". If these minimum requirements are not satisfied i.e. if a person has been, even slightly, influenced by personal emotions, feelings, instincts, or culturally specific moral codes and norms, then the analysis may be termed irrational, due to the injection of subjective bias.
Modern cognitive science and neuroscience show that studying the role of emotion in mental function (including topics ranging from flashes of scientific insight to making future plans), that no human has ever satisfied this criterion, except perhaps a person with no affective feelings, for example, an individual with a massively damaged amygdala or severe psychopathy. Thus, such an idealized form of rationality is best exemplified by computers, and not people. However, scholars may productively appeal to the idealization as a point of reference. In his book, "The Edge of Reason: A Rational Skeptic in an Irrational World," British philosopher Julian Baggini sets out to debunk myths about reason (e.g., that it is "purely objective and requires no subjective judgment").
Theoretical and practical.
Kant had distinguished theoretical from practical reason. Rationality theorist Jesús Mosterín makes a parallel distinction between theoretical and practical rationality, although, according to him, reason and rationality are not the same: reason would be a psychological faculty, whereas rationality is an optimizing strategy. Humans are not entirely rational, but they can think and behave rationally or not, depending on whether they apply, explicitly or implicitly, the strategy of theoretical and practical rationality to the thoughts they accept and to the actions they perform.
The distinction is also described as that between epistemic rationality, the attempt to form beliefs in an unbiased manner, and instrumental rationality.
Theoretical rationality has a formal component that reduces to logical consistency and a material component that reduces to empirical support, relying on our inborn mechanisms of signal detection and interpretation. Mosterín distinguishes between involuntary and implicit belief, on the one hand, and voluntary and explicit acceptance, on the other. Theoretical rationality can more properly be said to regulate our acceptances than our beliefs. Practical rationality is the strategy for living one's best possible life, achieving your most important goals and your own preferences in as far as possible.
Examples in different fields.
Logic.
As the study of arguments that are correct in virtue of their form, logic is of fundamental importance in the study of rationality. The study of rationality in logic is more concerned with epistemic rationality, that is, attaining beliefs in a rational manner, than instrumental rationality.
Economics.
Rationality plays a key role in economics and there are several strands to this. Firstly, there is the concept of instrumentality—basically the idea that people and organisations are instrumentally rational—that is, adopt the best actions to achieve their goals. Secondly, there is an axiomatic concept that rationality is a matter of being logically consistent within your preferences and beliefs. Thirdly, people have focused on the accuracy of beliefs and full use of information—in this view, a person who is not rational has beliefs that do not fully use the information they have.
Debates within economic sociology also arise as to whether or not people or organizations are "really" rational, as well as whether it makes sense to model them as such in formal models. Some have argued that a kind of bounded rationality makes more sense for such models.
Others think that any kind of rationality along the lines of rational choice theory is a useless concept for understanding human behavior; the term "homo economicus" (economic man: the imaginary man being assumed in economic models who is logically consistent but amoral) was coined largely in honor of this view. Behavioral economics aims to account for economic actors as they actually are, allowing for psychological biases, rather than assuming idealized instrumental rationality.
Artificial intelligence.
Within artificial intelligence, a "rational agent" is typically one that maximizes its expected utility, given its current knowledge. Utility is the usefulness of the consequences of its actions. The utility function is arbitrarily defined by the designer, but should be a function of "performance", which is the directly measurable consequences, such as winning or losing money. In order to make a safe agent that plays defensively, a nonlinear function of performance is often desired, so that the reward for winning is lower than the punishment for losing. An agent might be rational within its own problem area, but finding the rational decision for arbitrarily complex problems is not practically possible. The rationality of human thought is a key problem in the psychology of reasoning.
International relations.
There is an ongoing debate over the merits of using “rationality” in the study of international relations (IR). Some scholars hold it indispensable. Others are more critical. Still, the pervasive and persistent usage of "rationality" in political science and IR is beyond dispute. "Rationality" remains ubiquitous in this field. Abulof finds that Some 40% of all scholarly references to "foreign policy" allude to "rationality"—and this ratio goes up to more than half of pertinent academic publications in the 2000s. He further argues that when it comes to concrete security and foreign policies, IR employment of rationality borders on "malpractice": rationality-based descriptions are largely either false or unfalsifiable; many observers fail to explicate the meaning of "rationality" they employ; and the concept is frequently used politically to distinguish between "us and them."