He asserted that the principle of motion was the separation of hot from cold, from which he endeavoured to explain the formation of the Earth and the creation of animals and humans.

[3] Beginning with primitive Matter, (identical with air mingled with Mind), by a process of thickening and thinning, arose cold and warmth, or water and fire, the one passive, the other active.

While the earth was hardening, the action of heat upon its moisture gave birth to animals, which at first were nourished by the mud from which they sprang, and gradually acquired the power of propagating their species.

It was just from this point of his physical theory that he seems to have passed into ethical speculation, by the proposition, that right and wrong are "not by nature but by custom" (Greek: οὐ φύσει ἀλλὰ νόμῳ)[1]—dogma possibly suggested to him by the contemporary Sophists.

Of the other doctrines of Archelaus, he asserted that the Earth was flat, but that the surface must be depressed towards the centre; for if it were absolutely level, the sun would rise and set everywhere at the same time.