Capital (economics)

In economics, capital consists of human-created assets that can enhance one's power to perform economically useful work. For example, a stone arrowhead is capital for a hunter-gatherer who can use it as a hunting instrument; similarly, roads are capital for inhabitants of a city. Capital is distinct from land and other non-renewable resources in that it can be increased by human labor, and does not include certain durable goods like homes and personal automobiles that are not used in the production of saleable goods and services. Adam Smith defined capital as "that part of man's stock which he expects to afford him revenue". In economic models, capital is an input in the production function. 
The total physical capital at any given moment in time is referred to as the capital stock (not to be confused with the capital stock of a business entity). Capital goods, real capital, or capital assets are already-produced, durable goods or any non-financial asset that is used in production of goods or services.
In Marxian economics, capital is money used to buy something only in order to sell it again to realize a profit. For Marx, capital only exists within the process of the economic circuit (represented by M-C-M')—it is wealth that grows out of the process of circulation itself, and for Marx it formed the basis of the economic system of capitalism. In more contemporary schools of economics, this form of capital is generally referred to as "financial capital" and is distinguished from "capital goods".
In narrow and broad uses.
Classical and neoclassical economics regard capital as one of the factors of production (alongside the other factors: land and labour). All other inputs to production are called intangibles in classical economics. This includes organization, entrepreneurship, knowledge, goodwill, or management (which some characterize as talent, social capital or instructional capital).
This is what makes it a factor of production:
These distinctions of convenience have carried over to contemporary economic theory. Adam Smith provided the further clarification that capital is a stock. As such, its value can be estimated at a point in time. By contrast, investment, as production to be added to the capital stock, is described as taking place over time ("per year"), thus a flow.
Marxian economics distinguishes between different forms of capital:
Earlier illustrations often described capital as physical items, such as tools, buildings, and vehicles that are used in the production process. Since at least the 1960s economists have increasingly focused on broader forms of capital. For example, investment in skills and education can be viewed as building up human capital or knowledge capital, and investments in intellectual property can be viewed as building up intellectual capital. These terms lead to certain questions and controversies discussed in those articles.
Modern types of capital.
Detailed classifications of capital that have been used in various theoretical or applied uses generally respect the following division:
Separate literatures have developed to describe both natural capital and social capital. Such terms reflect a wide consensus that nature and society both function in such a similar manner as traditional industrial infrastructural capital, that it is entirely appropriate to refer to them as different types of capital in themselves. In particular, they can be used in the production of other goods, are not used up immediately in the process of production, and can be enhanced (if not created) by human effort.
There is also a literature of intellectual capital and intellectual property law. However, this increasingly distinguishes means of capital investment, and collection of potential rewards for patent, copyright (creative or individual capital), and trademark (social trust or social capital) instruments.
Building on Marx, and on the theories of the sociologist and philosopher Pierre Bourdieu, scholars have recently argued for the significance of "culinary capital" in the arena of food. The idea is that the production, consumption, and distribution of knowledge about food can confer power and status. 
Interpretations.
Within classical economics, Adam Smith ("Wealth of Nations", Book II, Chapter 1) distinguished fixed capital from circulating capital. The former designated physical assets not consumed in the production of a product (e.g. machines and storage facilities), while the latter referred to physical assets consumed in the process of production (e.g. raw materials and intermediate products). For an enterprise, both were types of capital.
Economist Henry George argued that financial instruments like stocks, bonds, mortgages, promissory notes, or other certificates for transferring wealth is not really capital, because "Their economic value merely represents the power of one class to appropriate the earnings of another" and "their increase or decrease does not affect the sum of wealth in the community".
Some thinkers, such as Werner Sombart and Max Weber, locate the concept of capital as originating in double-entry bookkeeping, which is thus a foundational innovation in capitalism, Sombart writing in "Medieval and Modern Commercial Enterprise" that:
Karl Marx adds a distinction that is often confused with David Ricardo's. In Marxian theory, variable capital refers to a capitalist's investment in labor-power, seen as the only source of surplus-value. It is called "variable" since the amount of value it can produce varies from the amount it consumes, "i.e.", it creates new value. On the other hand, constant capital refers to investment in non-human factors of production, such as plant and machinery, which Marx takes to contribute only its own replacement value to the commodities it is used to produce.
Investment or capital accumulation, in classical economic theory, is the production of increased capital. Investment requires that some goods be produced that are not immediately consumed, but instead used to produce other goods as capital goods. Investment is closely related to saving, though it is not the same. As Keynes pointed out, saving involves not spending all of one's income on current goods or services, while investment refers to spending on a specific type of goods, "i.e.", capital goods.
Austrian School economist Eugen Boehm von Bawerk maintained that capital intensity was measured by the roundaboutness of production processes. Since capital is defined by him as being goods of higher-order, or goods used to produce consumer goods, and derived their value from them, being future goods.
Human development theory describes human capital as being composed of distinct social, imitative and creative elements:
This theory is the basis of triple bottom line accounting and is further developed in ecological economics, welfare economics and the various theories of green economics. All of which use a particularly abstract notion of capital in which the requirement of capital being produced like durable goods is effectively removed.
The Cambridge capital controversy was a dispute between economists at Cambridge, Massachusetts based MIT and University of Cambridge in the UK about the measurement of capital. The Cambridge, UK economists, including Joan Robinson and Piero Sraffa claimed that there is no basis for aggregating the heterogeneous objects that constitute 'capital goods.'
Political economists Jonathan Nitzan and Shimshon Bichler have suggested that capital is not a productive entity, but solely financial and that capital values measure the relative power of owners over the broad social processes that bear on profits.