3. Change and interaction

In bed this morning the following dialectical ideas on the natural sciences came into my head:

The subject of natural science — moving matter, bodies. Bodies cannot be separated from motion, their forms and kinds can only be known through motion, of bodies apart from motion, apart from any relation to other bodies, nothing can be asserted. Only in motion does a body reveal what it is. Natural science therefore knows bodies by considering them in their relation to one another, in motion. The knowledge of the different forms of motion is the knowledge of bodies. The investigation of these different forms of motion is therefore the chief subject of natural science. (Engels to Marx, May 30, 1873.)

Motion is the mode of existence of matter. Never anywhere has there been matter without motion, nor can there be. (Engels, Anti-Dühring, part 1, chap. 6.)

Motion in the most general sense, conceived as the mode of existence, the inherent attribute of matter, comprehends all changes and processes occurring in the universe, from mere change of place right to thinking. (Engels, Dialectics of Nature.)