We know truth, not only by reason, but also by the heart.
Contradiction is not a sign of falsity, nor the lack of contradiction a sign of truth.
Man is to himself the most wonderful object in nature; for he cannot conceive what the body is, still less what the mind is, and least of all how a body should be united to a mind. This is the consummation of his difficulties, and yet it is his very being.
I have made this [letter] longer, because I have not had the time to make it shorter.
Clarity of mind means clarity of passion, too; this is why a great and clear mind loves ardently and sees distinctly what it loves.
The eternal silence of these infinite spaces fills me with dread.
If all men knew what each said of the other, there would not be four friends in the world.
People are usually more convinced by reasons they discovered themselves than by those found by others.
Our notion of symmetry is derived from the human face. Hence, we demand symmetry horizontally and in breath only, not vertically nor in depth.
Few men speak humbly of humility, chastely of chastity, skeptically of skepticism.