Vanity is but the surface.

No one is offended at not seeing everything; but one does not like to be mistaken, and that perhaps arises from the fact that man naturally cannot see everything, and that naturally he cannot err in the side he looks at, since the perceptions of our senses are always true.

(Man,) the glory and the scandal of the universe.

You see, if the height of the mercury [barometer] column is less on the top of a mountain than at the foot of it (as I have many reasons for believing, although everyone who has so far written about it is of the contrary opinion), it follows that the weight of the air must be the sole cause of the phenomenon, and not that abhorrence of a vacuum, since it is obvious that at the foot of the mountain there is more air to have weight than at the summit, and we cannot possibly say that the air at the foot of the mountain has a greater aversion to empty space than at the top.

All men seek happiness. This is without exception. Whatever different means they employ, they all tend to this end. The cause of some going to war, and of others avoiding it, is the same desire in both, attended with different views. The will never takes the least step but to this object. This is the motive of every action of every man, even of those who hang themselves.

I can readily conceive of a man without hands or feet; and I could conceive of him without a head, if experience had not taught me that by this he thinks, Thought then, is the essence of man, and without this we cannot conceive of him.

The arithmetical machine produces effects that approach nearer to thought than all the actions of animals. But it does nothing that would enable us to attribute will to it, as to the animals.