It is not to be forgotten that what we call rational grounds for our beliefs are often extremely irrational attempts to justify our instincts.

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

Try to learn something about everything and everything about something.

Trust a witness in all matters in which neither his self-interest, his passions, his prejudices, nor the love of the marvellous is strongly concerned. When they are involved, require corroborative evidence in exact proportion to the contravention of probability by the thing testified.

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 one of the most saddening things in life that, try as we may, we can never be certain of making people happy, whereas we can almost always be certain of making them unhappy.

Regarded anatomically, the resemblances between the foot of Man and the foot of the Gorilla are far more striking and important than the differences... be the differences between the hand and foot of Man and those of the Gorilla what they may the differences between those of the Gorilla and those of the lower Apes are much greater.