I hold that it is only when we can prove everything we assert that we understand perfectly the thing under consideration.

It is necessary to believe that the mixture of evil has produced the greatest possible good: otherwise the evil would not have been permitted.

And there must be simple substances, because there are compounds; for the compound is nothing but a collection or aggregatum of simples.

He who hasn't tasted bitter things hasn't earned sweet things.

Our reasonings are grounded upon two great principles, that of contradiction, in virtue of which we judge false that which involves a contradiction, and true that which is opposed or contradictory to the false.

I don't say that bodies like flint, which are commonly called inanimate, have perceptions and appetition; rather they have something of that sort in them, as worms are in cheese.

He who understands Archimedes and Apollonius will admire less the achievements of the foremost men of later times.