Is my understanding only blindness to my own lack of understanding? It often seems so to me.

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.

I am sitting with a philosopher in the garden; he says again and again 'I know that that’s a tree', pointing to a tree that is near us. Someone else arrives and hears this, and I tell him: 'This fellow isn’t insane. We are only doing philosophy.

I might say: if the place I want to get to could only be reached by way of a ladder, I would give up trying to get there. For the place I really have to get to is a place I must already be at now. Anything that I might reach by climbing a ladder does not interest me.

I act with complete certainty. But this certainty is my own.

In philosophy it is always good to put a question instead of an answer to a question. For an answer to the philosophical question may easily be unfair; disposing of it by means of another question is not.