The duty of a philosopher is clear. He must take every pain to ascertain the truth; and, having arrived at a conclusion, he should noise it abroad far and wide, utterly regardless of what opinions he shocks.

The clergy, with a few honorable exceptions, have in all modern countries been the avowed enemies of the diffusion of knowledge, the danger of which to their own profession they, by a certain instinct, seem always to have perceived.

The great enemy of knowledge is not error, but inertness. All that we want is discussion; and then we are sure to do well, no matter what our blunders may be. One error conflicts with another, each destroys its opponent, and truth is evolved.

Sir, the slowness of genius is hard to bear, but the slowness of mediocrity is insufferable.

Society prepares the crime; the criminal commits it.

First doubt, then inquire, then discover. This has been the process with all our great thinkers.

The faculty of art is to change events; the faculty of science is to foresee them. The phenomena with which we deal are controlled by art; they are predicted by science.