Men fear thought as they fear nothing else on earth -- more than ruin, more even than death. Thought is subversive and revolutionary, destructive and terrible, thought is merciless to privilege, established institutions, and comfortable habits; thought is anarchic and lawless, indifferent to authority, careless of the well-tried wisdom of the ages. Thought looks into the pit of hell and is not afraid ... Thought is great and swift and free, the light of the world, and the chief glory of man.

Conquer the world by intelligence, and not merely by being slavishly subdued by the terror that comes from it.

A stupid man's report of what a clever man says can never be accurate, because he unconsciously translates what he hears into something he can understand.

Ser optimista o pesimista es cuestion de temperamento, no de razones.

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.

Of course not. After all, I may be wrong.

Even when the experts all agree, they may well be mistaken.