As a well-spent day brings happy sleep, so life well used brings happy death.

Life well spent is long.

Shun those studies in which the work that results dies with the worker.

Whoever in discussion adduces authority uses not intellect but rather memory.

Iron rusts from disuse; stagnant water loses its purity and in cold weather becomes frozen; even so does inaction sap the vigor of the mind.

It is easier to resist at the beginning than at the end.

Necessity is the mistress and guardian of Nature.

Human subtlety...will never devise an invention more beautiful, more simple or more direct than does nature, because in her inventions nothing is lacking, and nothing is superfluous.

Mechanics is the paradise of the mathematical sciences because by means of it one comes to the fruits of mathematics.

I am not to blame for putting forward, in the course of my work on science, any general rule derived from a previous conclusion.