At the age of eleven, I began Euclid, with my brother as my tutor. ... I had not imagined that there was anything so delicious in the world. After I had learned the fifth proposition, my brother told me that it was generally considered difficult, but I had found no difficulty whatsoever. This was the first time it had dawned on me that I might have some intelligence.

The raw fruits of the earth were made for human sustenance. Even the white tails of rabbits, according to some theologians, have a purpose, namely to make it easier for sportsmen to shoot them. There are, it is true, some inconveniences: lions and tigers are too fierce, the summer is too hot, and the winter too cold. But these things only began after Adam ate the apple; I before that, all animals were vegetarians, and the season was always spring. If only Adam had been content with peaches and nectarines, grapes and pears and pineapples, these blessings would still be ours.

All knowledge, we feel, must be built up upon our instinctive beliefs; and if these are rejected, nothing is left.

What the world needs is not dogma but an attitude of scientific inquiry.

The opinions that are held with passion are always those for which no good ground exists; indeed the passion is the measure of the holders lack of rational conviction. Opinions in politics and religion are almost always held passionately.

I think it would be just to say the most essential characteristic of mind is memory, using this word in its broadest sense to include every influence of past experience on present reactions.

Unrestricted nationalism is, in the long run, incompatible with world peace.