The foundation of morality is to have done, once and for all, with lying.

In matters of intellect, follow your reason as far as it will take you, without regard for any other consideration.

Science reckons many prophets, but there is not even a promise of a Messiah.

The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness.

The ultimate court of appeal is observation and experiment... not authority.

In truth, the laboratory is the forecourt of the temple of philosophy, and whoso has not offered sacrifices and undergone purification there has little chance of admission into the sanctuary.

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.