We live in the best of all possible worlds

The greatness of a life can only be estimated by the multitude of its actions. We should not count the years, it is our actions which constitute our life.

He who understands Archimedes and Apollonius will admire less the achievements of the foremost men of later times.

Nihil est sine ratione. There is nothing without a reason.

The knowledge which we have acquired ought not to resemble a great shop without order, and without an inventory; we ought to know what we possess, and be able to make it serve us in need.

There never is absolute birth nor complete death, in the strict sense, consisting in the separation of the soul from the body. What we call births are developments and growths, while what we call deaths are envelopments and diminutions.

Our reasonings are grounded upon two great principles, that of contradiction, in virtue of which we judge false that which involves a contradiction, and true that which is opposed or contradictory to the false.