Life is doubt, and faith without doubt is nothing but death.

Man habitually sacrifices his life to his purse, but he sacrifices his purse to his vanity.

A lot of good arguments are spoiled by some fool who knows what he is talking about.

The skeptic does not mean him who doubts, but him who investigates or researches, as opposed to him who asserts and thinks that he has found.

And usually [the philosopher] philosophizes either in order to resign himself to life, or to seek some finality in it, or to distract himself and forget his griefs, or for pastime and amusement.

Chemistry ought to be not for chemists alone.

What we believe to be the motives of our conduct are usually but the pretexts for it.