A tautology's truth is certain, a proposition's possible, a contradiction's impossible. (Certain, possible, impossible: here we have the first indica… - Ludwig Wittgenstein

A tautology's truth is certain, a proposition's possible, a contradiction's impossible.

The aim of the book is to set a limit to thought, or rather — not to thought, but to the expression of thoughts: for in order to be able to set a limit to thought, we should have to find both sides of the limit thinkable (i.e. we should have to be able to think what cannot be thought). It will therefore only be in language that the limit can be set, and what lies on the other side of the limit will simply be nonsense.

For remember that in general we don't use language according to strict rules — it hasn't been taught to us by means of strict rules, either. We, in our discussions on the other hand, constantly compare language with a calculus preceding to exact rules.

Philosophers are often like little children, who first scribble random lines on a piece of paper with their pencils, and now ask an adult "What is that?"