In the sciences, the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man.

Nothing can be taught to a man, only it's possibly to help him to discover it inside.

In the long run my observations have convinced me that some men, reasoning preposterously, first establish some conclusion in their minds which, either because of its being their own or because of their having received it from some person who has their entire confidence, impresses them so deeply that one finds it impossible ever to get it out of their heads.

To command their professors of astronomy to refute their own observations is to command them not to see what they do see and not to understand what they do understand.

The Divine intellect indeed knows infinitely more propositions [than we can ever know]. But with regard to those few which the human intellect does understand, I believe that its knowledge equals the Divine in objective certainty.

We must say that there are as many squares as there are numbers.

God is known by nature in his works, and by doctrine in his revealed word.