The natural sciences have been prolifically active and have gathered together an ever growing mass of material. But philosophy has remained just as alien to them as they have remained alien to philosophy. Their momentary union was only a fantastic illusion. The will was there, but not the means. Even historiography only incidentally takes account of natural science, which it sees as contributing to enlightenment, utility and a few great discoveries. But natural science has intervened in and transformed human life all the more practically through industry and has prepared the conditions for human emancipation, however much its immediate effect was to complete the process was to complete the process of dehumanization.
Industry is the real historical relationship of nature, and hence of natural science, to man. If it is then conceived as the exoteric revelation of man's essential powers, the human essence of nature or the natural essence of man can also be understood. Hence natural science will lose its abstractly material, or rather idealist, orientation and become the basis of a human science, just as it has already become -- though in an estranged form -- the basis of actual human life. The idea of one basis for life and another for science is from the very outset a lie. Nature as it comes into being in human history -- in the act of creation of human society -- is the true nature of man; hence nature as it comes into being through industry, though in an estranged form, is true anthropological nature.
Sense perception (see Feuerbach) must be the basis of all science.
Only when science starts out from sense perception in the dual form of sensuous consciousness and sensuous need -- i.e., only when science starts out from nature -- is it real science. The whole of history is a preparation, a development, for "man" to become the object of sensuous consciousness and for the needs of "man as man" to become [sensuous] needs.
History itself is a real part of natural history and of nature's becoming man. Natural science will, in time, subsume the science of man, just as the science of man will subsume natural science: there will be one science.
Man is the immediate object of natural science; for immediate sensuous nature for man is, immediately, human sense perception (an identical expression) in the form of the other man who is present in his sensuous immediacy for him. His own sense perception only exists as human sense perception for himself through the other man. But nature is the immediate object of the science of man. Man's first object -- man -- is nature, sense perception; and the particular sensuous human powers, since they can find objective realization only in natural objects, can find self-knowledge only in the science of nature in general. The element of thought itself, the element of the vital expression of thought -- language -- is sensuous nature. The social reality of nature and human natural science or the natural science of man are identical expressions.
It can be seen how the rich man and the wealth of human need take the place of the wealth and poverty of political economy. The rich man is simultaneously the man in need of totality of vital human expression; he is the man in whom his own realization exists as inner necessity, as need. Given socialism, not only man's wealth but also his poverty acquire a human and hence a social significance. Poverty is the passive bond which makes man experience his greatest wealth -- the other man -- as need. The domination of the objective essences within me, the sensuous outburst of my essential activity, is passion, which here becomes the activity of my being.