Marx answered: The prime motive power of human society, which is responsible for the changes of human consciousness and thought, or which causes the various social institutions and conflicts to arise, does not originate, in the first place, from thought, from the Idea, from the world-reason or the world-spirit, but from the material conditions of life. The basis of human history is therefore material. The material conditions of life--that is, the manner in which men as social beings, with the aid of environing nature, and of their own in-dwelling physical and intellectual qualities, shape their material life, provide for their sustenance, and produce, distribute and exchange the necessary goods for the satisfaction of their needs. Of all categories of material conditions of existence, the most important is production of the necessary means of life. And this is determined by the nature of the productive forces. These are of two kinds: inanimate and personal. The inanimate productive forces are: soil, water, climate, raw materials, tools and machines. The personal productive forces are: the labourers, the inventors, discoverers, engineers, and finally, the qualities of the race--the inherited capacities of specific groups of men, which facilitate work. The foremost place among the productive forces belongs to the manual and mental labourers; they are the real creators of exchange-value in capitalist society. The next place of importance is taken by modern technology, which is an eminently revolutionising force in society.--("Capital" (German), Vol. I., Chapters 1, 12, 13 and 14, "Poverty of Philosophy" (German edition, 1885, pp. 100-101.)) So much for the conception "Productive Forces," which plays an important part with Marx. We come now to the other equally important notion, "Conditions of production." By this phrase Marx understands the legal and State forms, ordinances and laws, as well as the grouping of social classes and sections: thus, the social conditions which regulate property and determine the reciprocal human relations in which production is carried on. The conditions of production are the work of men in society. Just as men produce various material goods out of the materials and forces made available to them by Nature, so they create out of the reactions of the productive forces upon the mind definite social, political, and legal institutions, as well as systems of religion, morals, and philosophy. "Men make their own history, but do not so spontaneously in conditions chosen by them, but on the contrary, in conditions which they have found ready to hand transmitted and given."--(Marx, "The Eighteenth Brumaire," I.)