Philosophy is not a theory but an activity.

Black seems to make a colour cloudy, but darkness doesn't. A ruby could thus keep getting darker without ever becoming cloudy; but if it became blackish red, it would become cloudy.

There is a truth in Schopenhauer’s view that philosophy is an organism, and that a book on philosophy, with a beginning and end, is a sort of contradiction. ... In philosophy matters are not simple enough for us to say ‘Let’s get a rough idea’, for we do not know the country except by knowing the connections between the roads.

Almost in the same way as earlier physicists are said to have found suddenly that they had too little mathematical understanding to be able to master physics; we may say that young people today are suddenly in the position that ordinary common sense no longer suffices to meet the strange demands life makes. Everything has become so intricate that for its mastery an exceptional degree of understanding is required. For it is not enough any longer to be able to play the game well; but the question is again and again: what sort of game is to be played now anyway?

What we cannot speak about we must pass over in silence.

One often makes a remark and only later sees how true it is.

A philosopher who is not taking part in discussions is like a boxer who never goes into the ring.