Engels on the Dialectics of Nature.

“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.”

 – Friedrich Engels, “Dialectics of Nature”