Every child knows a nation which ceased to work, I will not say for a year, but even for a few weeks, would perish. Every child knows, too, that the masses of products corresponding to the different needs required different and quantitatively determined masses of the total labor of society. That this necessity of the distribution of social labor in definite proportions cannot possibly be done away with by a particular form of social production but can only change the mode of its appearance , is self-evident. No natural laws can be done away with. What can change in historically different circumstances is only the form in which these laws assert themselves. And the form in which this proportional distribution of labor asserts itself, in the state of society where the interconnection of social labor is manifested in the private exchange of the individual products of labor, is precisely the exchange value of these products. Science consists precisely in demonstrating how the law of value asserts itself. So that if one wanted at the very beginning to "explain" all the phenomenon which seemingly contradict that law, one would have to present science before science. It is precisely Ricardo's mistake that in his first chapter on value [ On the Principles of Political Economy, and Taxation , Page 479] he takes as given all possible and still to be developed categories in order to prove their conformity with the law of value. On the other hand, as you correctly assumed, the history of the theory certainly shows that the concept of the value relation has always been the same more or less clear, hedged more or less with illusions or scientifically more or less definite. Since the thought process itself grows out of conditions, is itself a natural process, thinking that really comprehends must always be the same, and can vary only gradually, according to maturity of development, including the development of the organ by which the thinking is done. Everything else is drivel. The vulgar economist has not the faintest idea that the actual everyday exchange relations can not be directly identical with the magnitudes of value. The essence of bourgeois society consists precisely in this, that a priori there is no conscious social regulation of production. The rational and naturally necessary asserts itself only as a blindly working average. And then the vulgar economist thinks he has made a great discovery when, as against the revelation of the inner interconnection, he proudly claims that in appearance things look different. In fact, he boasts that he holds fast to appearance, and takes it for the ultimate. Why, then, have any science at all? But the matter has also another background. Once the interconnection is grasped, all theoretical belief in the permanent necessity of existing conditions collapses before their collapse in practice. Here, therefore, it is absolutely in the interest of the ruling classes to perpetuate a senseless confusion. And for what other purpose are the sycophantic babblers paid, who have no other scientific trump to play save that in political economy one should not think at all? But satis superque [enough and to spare]. In any case it shows what these priests of the bourgeoisie have come down to, when workers and even manufacturers and merchants understand my book [Capital] and find their way about in it, while these "learned scribes" (!) complain that I make excessive demands on their understanding....
Letters: Marx-Engels Correspondence 1868