Ludwig Wittgenstein

If I cannot say a priori what elementary propositions there are, then the attempt to do so must lead to obvious nonsense.

A tautology's truth is certain, a 's possible, a contradiction's impossible. (Certain, possible, impossible: here we have the first indication of the scale that we need in the theory of probability.)

The world and life are one.

Propositions are truth-functions of elementary propositions. (An elementary proposition is a truth-function of itself.)

Whereof one cannot speak, thereof one must be silent.

Philosophy aims at the logical clarification of thoughts. Philosophy is not a body of doctrine but an activity. A philosophical work consists essentially of elucidations. Philosophy does not result in 'philosophical propositions', but rather in the clarification of propositions. Without philosophy thoughts are, as it were, cloudy and indistinct: its task is to make them clear and to give them sharp boundaries.

The subject does not belong to the world, but it is a limit of the world.

The limits of my language mean the limits of my world.

The world of the happy is quite different from the world of the unhappy.

It is quite impossible for a proposition to state that it itself is true.

The thought is the significant proposition.

There are, indeed, things that cannot be put into words. They make themselves manifest. They are what is mystical.