To be humane, we must ever be ready to pronounce that wise, ingenious and modest statement 'I do not know'.

To understand the Universe, you must understand the language in which it's written, the language of Mathematics.

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.

That sculpture is more admirable than painting for the reason that it contains relief and painting does not is completely false. ... Rather, how much more admirable the painting must be considered, if having no relief at all, it appears to have as much as sculpture!

It has always seemed to me extreme presumptuousness on the part of those who want to make human ability the measure of what nature can and knows how to do, since, when one comes down to it, there is not one effect in nature, no matter how small, that even the most speculative minds can fully understand.

E pur si muove. "Albeit It does move". (That's what Galileo purportedly muttered after torturers forced him to recant his theory that the earth orbits the sun.)

Two truths cannot contradict one another.