Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous.

Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.…'Tis not contrary to reason to prefer the destruction of the whole world to the scratching of my finger.

The perfect philosophy of the natural kind [= the perfect physics] only staves off our ignorance a little longer; just as, perhaps, the most perfect philosophy of the moral or metaphysical kind [= the most perfect philosophy, in the 21st century sense of the word] serves only to show us more of how ignorant we are. So both kinds of philosophy eventually lead us to a view of human blindness and weakness—a view that confronts us at every turn despite our attempts to get away from it.

Reason is, and ought only to be the slave of the passions.

Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.

Stercus accidit.

Nothing is more usual than for philosophers to encroach upon the province of grammarians; and to engage in disputes of words, while they imagine that they are handling controversies of the deepest importance and concern.

Indulge your passion for science…but let your science be human, and such as may have a direct reference to action and society. Be a philosopher; but amidst all your philosophy, be still a man.

Should a traveler, returning from a far country, bring us an account of men wholly different from any with whom we were ever acquainted, men who were entirely divested of avarice, ambition, or revenge, who knew no pleasure but friendship, generosity, and public spirit, we should immediately, from these circumstances, detect the falsehood and prove him a liar with the same certainty as if he had stuffed his narration with stories of centaurs and dragons, miracles and prodigies.