To be and to think are one and the same for us.

An Individual, whatever species it might be, is nothing in the Universe. A hundred, a thousand individuals are still nothing. The species are the only creatures of Nature, perpetual creatures, as old and as permanent as it. In order to judge it better, we no longer consider the species as a collection or as a series of similar individuals, but as a whole independent of number, independent of time, a whole always living, always the same, a whole which has been counted as one in the works of creation, and which, as a consequence, makes only a unity in Nature.

Only well-written works will descend to posterity. Fulness of knowledge, interesting facts, even useful inventions, are no pledge of immortality, for they may be employed by more skilful hands; they are outside the man; the style is the man himself.

There is nothing good in love but the physical part.

There are several kinds of truths, and it is customary to place in the first order mathematical truths, which are, however, only truths of definition. These definitions rest upon simple, but abstract, suppositions, and all truths in this category are only constructed, but abstract, consequences of these definitions ... Physical truths, to the contrary, are in no way arbitrary, and do not depend on us.

One can descend by imperceptible degree from the most perfect creature to the most shapeless matter, from the best-organised animal to the roughest mineral.

The human mind cannot create anything. It produces nothing until having been fertilized by experience and meditation; its acquisitions are the germs of its production.