Productive forces, productive powers, or forces of production (German: Produktivkräfte) is a central idea in Marxism and historical materialism. In Karl Marx and Friedrich Engels' own critique of political economy, it refers to the combination of the means of labor (tools, machinery, land, infrastructure, and so on) with human labour power. Marx and Engels probably derived the concept from Adam Smith's reference to the "productive powers of labour" (see e.g. chapter 8 of The Wealth of Nations (1776)), although the German political economist Friedrich List also mentions the concept of "productive powers" in The National System of Political Economy (1841). All those forces which are applied by people in the production process (body and brain, tools and techniques, materials, resources, quality of workers' cooperation, and equipment) are encompassed by this concept, including those management and engineering functions technically indispensable for production (as contrasted with social control functions). Human knowledge can also be a productive force. Together with the social and technical relations of production, the productive forces constitute a historically specific mode of production. Labor Karl Marx emphasized that with few exceptions means of labour are not a productive force unless they are actually operated, maintained and conserved by living human labour. Without applying living human labour, their physical condition and value would deteriorate, depreciate, or be destroyed (an example would be a ghost town or capital depreciation due to strike action). Capital itself, being one of the factors of production, comes to be viewed in capitalist society as a productive force in its own right, independent from labour, a subject with "a life of its own". Indeed, Marx sees the essence of what he calls "the capital relation" as being summarised by the circumstance that "capital buys labour", i.e. the power of property ownership to command human energy and labour-time, and thus of inanimate "things" to exert an autonomous power over people. What disappears from view is that the power of capital depends in the last instance on human cooperation. The productive power of cooperation comes to be viewed as the productive power of capital, because it is capital which forcibly organises people, rather than people organising capital. Marx regarded this as a supreme reification. Unlike British classical economics, Marxian economics classifies financial capital as being an element of the relations of production, rather than the factors or forces of production ("not a thing, but a social relation between