(The general nature of dialectics to be developed as the science of inter-connections, in contrast to metaphysics.)
It is, therefore, from the history of nature and human society that the laws of dialectics are abstracted. For they are nothing but the most general laws of these two aspects of historical development, as well as of thought itself. And indeed they can be reduced in the main to three:
The law of the transformation of quantity into quality and vice versa;
The law of the interpenetration of opposites;
The law of the negation of the negation.
All three are developed by Hegel in his idealist fashion as mere laws of thought: the first, in the first part of his Logic, in the Doctrine of Being; the second fills the whole of the second and by far the most important part of his Logic, The Doctrine of Essence; finally the third figures as the fundamental law for the construction of the whole system. The mistake lies in the fact that these laws are foisted on nature and history as laws of thought, and not deduced from them. This is the source of the whole forced and often outrageous treatment; the universe, willy-nilly, has to conform to a system of thought which itself is only the product of a definite stage of evolution of human thought. If we turn the thing round, then everything becomes simple, and the dialectical laws that look so extremely mysterious in idealist philosophy at once become simple and clear as noonday.
Moreover, anyone who is even only slightly acquainted with Hegel will be aware that in hundreds of passages Hegel is capable of giving the most striking individual illustrations of the dialectical laws from nature and history.
We are not concerned here with writing a handbook of dialectics, but only with showing that the dialectical laws are real laws of development of nature, and therefore are valid also for theoretical natural science. …
1. The law of the transformation of quantity into quality and vice versa. For our purpose, we can express this by saying that in nature, in a manner exactly fixed for each individual case, qualitative changes can only occur by the quantitative addition or quantitative subtraction of matter or motion (so-called energy).
All qualitative differences in nature rest on differences of chemical composition or on different quantities or forms of motion (energy) or, as is almost always the case, on both. Hence it is impossible to alter the quality of a body without addition or subtraction of matter or motion, i.e., without quantitative alteration of the body concerned. In this form, therefore, Hegel’s mysterious principle appears not only quite rational but even rather obvious.
Friedrich Engels, Dialectics of Nature, Progress Publishers, Moscow, 1976, 62-63
Part one/to be continued…