At the core of all well-founded belief lies belief that is unfounded.

All testing, all confirmation and disconfirmation of a hypothesis takes place already within a system. And this system is not a more or less arbitrary and doubtful point of departure for all our arguments: no, it belongs to the essence of what we call an argument. The system is not so much as the point of departure, as the element in which arguments have their life.

If you tried to doubt everything you would not get as far as doubting anything. The game of doubting itself presupposes certainty.

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

Certainty is as it were a tone of voice in which one declares how things are, but one does not infer from the tone of voice that one is justified.

If you do know that here is one hand, we'll grant you all the rest.