Both capital’s learned philosophers and Marxists would do well to pay attention to the following words. Or perhaps they are for all but the above, whose ideologies are equally delimited. Contradiction is the engine of the world.
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Truth, the cognition of which is the business of philosophy, was in the hands of Hegel no longer an aggregate of finished dogmatic statements, which, once discovered, had merely to be learned by heart. Truth lay now in the process of cognition itself, in the long historical development of science, which mounts from lower to ever higher levels of knowledge without ever reaching, by discovering so-called absolute truth, a point at which it can proceed no further, where it would have nothing more to do than to fold its hands and gaze with wonder at the absolute truth to which it had attained. And what holds good for the realm of philosophical knowledge holds good also for that of every other kind of knowledge and also for practical action. Just as knowledge is unable to reach a complete conclusion in a perfect, ideal condition of humanity, so is history unable to do so; a perfect society, a perfect “state”, are things which can only exist in imagination. On the contrary, all successive historical systems are only transitory stages in the endless course of development of human society from the lower to the higher. Each stage is necessary, and therefore justified for the time and conditions to which it owes its origin. But in the face of new, higher conditions which gradually develop in its own womb, it loses vitality and justification. It must give way to a higher stage which will also in its turn decay and perish. Just as the bourgeoisie by large-scale industry, competition, and the world market dissolves in practice all stable time-honored institutions, so this dialectical philosophy dissolves all conceptions of final, absolute truth and of absolute states of humanity corresponding to it. For it [dialectical philosophy], nothing is final, absolute, sacred. It reveals the transitory character of everything and in everything; nothing can endure before it except the uninterrupted process of becoming and of passing away, of endless ascendancy from the lower to the higher. And dialectical philosophy itself is nothing more than the mere reflection of this process in the thinking brain. It has, of course, also a conservative side; it recognizes that definite stages of knowledge and society are justified for their time and circumstances; but only so far. The conservatism of this mode of outlook is relative; its revolutionary character is absolute — the only absolute dialectical philosophy admits.
Frederick Engels, Ludwig Feuerbach and the End of Classical German Philosophy, 1886
Complete text at Marxists Internet Archive