Labour power (in ; in ) is a key concept used by Karl Marx in his critique of capitalist political economy. Marx distinguished between the capacity to do work, labour power, from the physical act of working, labour. Labour power exists in any kind of society, but on what terms it is traded or combined with means of production to produce goods and services has historically varied greatly. Under capitalism, according to Marx, the productive powers of labour appear as the creative power of capital. Indeed, "labour power at work" becomes a component of capital, it functions as working capital. Work becomes just work, workers become an abstract labour force, and the control over work becomes mainly a management prerogative. Definition Karl Marx introduces the concept in chapter 6 of the first volume of Capital, as follows: "By labour-power or capacity for labour is to be understood the aggregate of those mental and physical capabilities existing in a human being, which he exercises whenever he produces a use-value of any description." He adds further on that: "Labour-power, however, becomes a reality only by its exercise; it sets itself in action only by working. But thereby a definite quantity of human muscle, nerve. brain, &c., is wasted, and these require to be restored." Another explanation of labour-power can be found in the introduction and second chapter of Marx's Wage Labour and Capital (1847). Marx also provided a short exposition of labour power in Value, Price and Profit (1865). Versus labour Marx adapted a distinction, in Hegel's Elements of the Philosophy of Right between labour power (Arbeitskraft) and labour (Arbeit) and gave this distinction a new significance. For Marx, Arbeitskraft, which he sometimes instead refers to as Arbeitsvermögen ("labour-ability" or "labour-capacity") refers to a "force of nature": the physical ability of human beings and other living things to perform work, including mental labour and skills such as manual dexterity, in addition to sheer physical exertion. Labour power is, in this sense, also the aspect of labour that becomes a commodity within capitalist society and is alienated from labourers when it is sold to capitalists. By contrast, "labour" may refer to all or any activity by humans (and other living creatures) that is concerned with producing goods or services (or what Marx calls use-values). In this sense, the usage of labour (per se) in Marxian economics is somewhat similar to the later concept,