"Labor first, and in close step with it, speech . . . those are the two essential stimuli under the influence of which the brain of an ape passed over gradually into that of a man. With the cultivation of the brain went hand in hand the cultivation of the sense organs . . . . The reactive effect of the development of the brain and its subject sense of consciousness growing clearer and clearer, of the capacity for abstraction and forming conclusion, upon labor and speech . . . all of this served continually to induce the further development of these two forces; a development which never came to a close and which, on the one hand, was powerfully promoted and, on the other, swung in a more definite direction by the new element added on with the appearance of the finished man . . . namely, society."

Thus, in this opinion, consciousness and science has its basis in the development of labor, or the growth of the human-social forces of production. It is first the labor of man applied to the world existing independently of man which fashions the contradiction between being and consciousness, a contradiction, moreover, which cannot be done away with except through the elimination of labor. Through the growth of the productive forces, bringing with it a change in the forms in which the material interaction between man and nature is accomplished, nature, society and consciousness, mutually interacting, also change. It is only because of the fact that man alters external nature by means of labor that his own nature and the whole complex of his life and interests are altered, and these having been changed, they change again the external world. If the human-active element is at first only the most primitive, corporeal activity, yet in connection with that activity arises intelligence, which by reaction transforms the simple activity into the more complicated.

From this point of view, "science" stands above classes only in that, like labor, it progressively develops with the forces of production in all forms of social life; for the necessity of labor remains intact in any form of society. But the more the productive forces develop, the more does the social elements condition the total process of development. Marx pointed out, for example, the fact that "in all forms of society where property in land prevails, the natural relation is still predominant; but in those where capital prevails, the social element outweighs." The closeness of the connection between the labor process and consciousness is clearly revealed by Marx in the Feuerbach section of Die Deutsche Ideologie, where he says :

"The division of labor really becomes a division only from the moment when a division enters between material and intellectual labor. From that moment, consciousness can really fancy itself as something other than the consciousness of existing practice." With the accelerated growth of the productive forces under capitalism, their theoretical expression, "science," also underwent such a development that its own influence upon the total process grew more and more significant. And as formerly labor developed new moments . . . the senses and consciousness . . . so later science also developed new tendencies peculiar to itself, which, however, leave untouched the basic fact that science is conditioned by the social needs, which in turn depend on the stage of development of the productive forces. Nothing perhaps shows this dependence more clearly than the present general crisis of bourgeois science, which runs parallel with the general economic crisis of capital. If capitalism restricts the further unfolding of the productive forces, it also restricts the extension of science. Neither the one nor the other can throw off its fetters except through the proletarian revolution; which is to say that only this revolution can still be regarded as "objective science." The further development of the rational elements immanent in science, that is, of the social forces of production, is the historical mission of the working class, which accordingly is to be identified with science. The scientists themselves become revolutionists, or else they cease to be scientists.