In order to acquire intellect one must need it. One loses it when it is no longer necessary.

Freedom of opinion is like health; both are individual, and no good general conception can be set up of either of them.

Without the errors which lie in the assumption of morality, man would have remained an animal.

Logic, too, also rests on assumptions that do not correspond to anything in the real world, e.g., on the assumption that there areequal things, that the same thing is identical at different points in time: but this science arose as a result of the opposite belief (that such things actually exist in the real world). And it is the same with mathematics, which would certainly never have arisen if it had been understood from the beginning that there is no such thing in nature as a perfectly straight line, a true circle, and absolute measure.

Not doubt, certainty is what drives one insane.

A subject for a great poet would be God's boredom after the seventh day of creation.

Doing ill to those on whom we have to make our power felt; for pain is a far more sensitive means for that purpose than pleasure: pain always asks concerning the cause, while pleasure is inclined to keep within itself and not look backward.