Philosophy limits the thinkable and therefore the unthinkable.

Every sign by itself seems dead. What gives it life?--In use it is alive. Is life breathed into it there?--Or is the use its life?

What is left over if I subtract the fact that my arms goes up from the fact that I raise my arm?

One cannot guess how a word functions. One has to look at its use and learn from that. But the difficulty is to remove the prejudice which stands in the way of doing this. It is not a stupid prejudice.

Nothing is more important for teaching us to understand the concepts we have than to construct fictitious ones.

Nothing is so difficult as not deceiving oneself.

It would strike me as ridiculous to want to doubt the existence of Napoleon; but if someone doubted the existence of the earth 150years ago, perhaps I should be more willing to listen, for now he is doubting our whole system of evidence.