They who depend upon manifest observations will philosophize better than those who persist in opinions repugnant to the senses.

The greatest wisdom is to get to know oneself.

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.)

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

Alas! Your dear friend and servant Galileo has been for the last month hopelessly blind; so that this heaven, this earth, this universe, which I by my marvelous discoveries and clear demonstrations had enlarged a hundred thousand times beyond the belief of the wise men of bygone ages, henceforward for me is shrunk into such a small space as is filled by my own bodily sensations.

Nature...does not act by means of many things when it can do so by means of a few.

The surface of the Moon is not smooth, uniform, and precisely spherical as a great number of philosophers believe it to be, but is uneven, rough, and full of cavities and prominences, being not unlike the face of the Earth, relieved by chains of mountains and deep valleys.