The sciences that are expressed by numbers or by other small signs, are easily learned; and... this facility rather than its demonstrability is what has made the fortune of algebra.

As a violin string or a harpsichord key vibrates and gives forth sound, so the cerebral fibres, struck by waves of sound, are stimulated to render or repeat the words that strike them.

A geometrician has learned to perform the most difficult demonstrations and calculations, as a monkey has learned to take his little hat off and on...

Man has been trained in the same way as animals. He has become an author, as they became beasts of burden.

What was man before the invention of words and the knowledge of language? An animal..

Let us not limit the resources of nature; they are infinite, especially when reinforced by great art.

Among animals, some learn to speak and sing; they remember tunes, and strike the notes as exactly as a musician. Others, for instance the ape, show more intelligence... would it be absolutely impossible to teach the ape a language? I do not think so.

A mere nothing, a tiny fibre, something that could never be found by the most delicate anatomy, would have made of Erasmus and Fontenelle two idiots, and Fontenelle himself speaks of this very fact in one of his best dialogues.

In general, the form and the structure of the brains of quadrupeds are almost the same as those of the brain of man...

The, diverse states of the soul are always correlative with those of the body.