To say that an idea is necessary is simply to affirm that we cannot conceive the contrary; and the fact that we cannot conceive the contrary of any belief may be a presumption, but is certainly no proof, of its truth.
There is nothing of permanent value (putting aside a few human affections) nothing that satisfies quiet reflection--except the sense of having worked according to one's capacity and light to make things clear and get rid of cant and shams of all sorts.
Time, whose tooth gnaws away everything else, is powerless against truth.
Veracity is the heart of morality.
The more rapidly truth is spread among mankind the better it will be for them. Only let us be sure that it is the truth.
It is wrong for a man to say that he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty.
Nothing great in science has ever been done by men, whatever their powers, in whom the divine afflatus of the truth-seeker was wanting.
History warns us that it is the customary fate of new truths to begin as heresies and to end as superstitions.
All truth, in the long run, is only common sense clarified.
Irrationally held truths may be more harmful than reasoned errors.
The scientific spirit is of more value than its products, and irrationally held truths may be more harmful than reasoned errors.