The beginning, middle, and end of the birth, growth, and perfection of whatever we behold is from contraries, by contraries, and to contraries; and whatever contrariety is, there is action and reaction, there is motion, diversity, multitude, and order, there are degrees, succession and vicissitude.

There is no law governing all things.

My son, I do not say these are foals and those asses, these little monkeys and those great baboons, as you would have me do. As I told you from the first, I regard them as earth's heroes. But I do not wish to believe them without cause, nor to accept those propositions whose antitheses (as you must have understood if you are not both blind and deaf) are so compellingly true.

Time is the father of truth, its mother is our mind.

The gems of philosophy are not less precious because they are not understood.

The stars in the sky are really other suns like our own, around which orbit other planets. (paraphrase)

The hammers must be swung in cadence, when more than one is hammering the iron.