Suppose someone follows the series "1,3,5,7, ..", and in writing the series 2x+1; and he asked himself "But am I always doing the same thing, or something different every time?" If from one day to the next someone promises: "Tomorrow I will give up smoking", does he say the same thing every day, or every day something different?

The common behavior of mankind is the system of reference by means of which we interpret an unknown language.

Hegel seems to me to be always wanting to say that things which look different are really the same. Whereas my interest is in showing that things which look the same are really different. I was thinking of using as a motto for my book a quotation from King Lear: 'I’ll teach you differences'. ... 'You’d be surprised' wouldn’t be a bad motto either.

You must always be puzzled by mental illness. The thing I would dread most, if I became mentally ill, would be your adopting a common sense attitude; that you could take it for granted that I was deluded.

In order to draw a limit to thinking, we should have to think both sides of this limit.

All mathematics is tautology.

Death is not an event in life: we do not live to experience death.