God alone is the author of all the motions in the world.

Illusory joy is often worth more than genuine sorrow.

Perfect numbers like perfect men are very rare.

There is nothing more ancient than the truth.

For to be possessed of a vigorous mind is not enough; the prime requisite is rightly to apply it.

In order to improve the mind, we ought less to learn, than to contemplate.

Each problem that I solved became a rule, which served afterwards to solve other problems.