The evolution of our spirit is blazed on the dark background of eternity by our individual wakes. Every person can, if he/she wishes, leave a more or less brilliant wake behind them.

It is clear that thought is not free if the profession of certain opinions makes it impossible to earn a living.

Science does not aim at establishing immutable truths and eternal dogmas; its aim is to approach the truth by successive approximations, without claiming that at any stage final and complete accuracy has been achieved.

Obviousness is always the enemy of correctness.

Mathematics is only the art of saying the same thing in different words.

From that awful encounter of the soul with the outer world, enunciation, wisdom, and charity are born; and with their birth a new life begins. To take into the inmost shrine of the soul the irresistible forces whose puppets we seem to be - Death and change, the irrevocableness of the past, and the powerlessness of Man before the blind hurry of the universe from vanity to vanity - to feel these things and know them is to conquer them.

Certain characteristics of the subject are clear. To begin with, we do not in this subject deal with particular things or particular properties: we deal formally with what can be said about any thing or any property. We are prepared to say that one and one are two, but not that Socrates and Plato are two.