Follow humbly wherever and to whatever abyss Nature leads, or you shall learn nothing.

Science is organized common sense where many a beautiful theory was killed by an ugly fact.

Veracity is the heart of morality.

'Infidel' is a term of reproach, which Christians and Mohammedans, in their modesty, agree to apply to those who differ from them.

Each such answer to the great question, invariably asserted by the followers of its propounder, if not by himself, to be complete and final, remains in high authority and esteem, it may be for one century, or it may be for twenty: but, as invariably, Time proves each reply to have been a mere approximation to the truth tolerable chiefly on account of the ignorance of those by whom it was accepted, and wholly intolerable when tested by the larger knowledge of their successors.

The foundation of all morality is to have done, once and for all, with lying; to give up pretending to believe that for which there is no evidence, and repeating unintelligible propositions about things beyond the possibilities of knowledge.

The scientific imagination always restrains itself within the limits of probability.