at all?
 "Is that something that one can forget?!"
 "In such circumstances, people do not say 'Perhaps we've all forgotten', and the like, but rather they assume that..."
 Our talk gets its meaning from the rest of our proceedings.
 We are asking ourselves: what do we do with a statement "I know..."? For it is not a question of mental processes or mental states.
And that is how one must decide whether something is knowledge or not.
 If someone doubted whether the earth had existed a hundred years ago, I should not understand, for this reason: I would not know what such a person would still allow to be counted as evidence and what not.
 "We could doubt every single one of these facts, but we could not doubt them all."
Wouldn't it be more correct to say: "we do not doubt them all". 
Our not doubting them all is simply our manner of judging, and therefore of acting.
 If a child asked me whether the earth was already there before my birth, I should answer him that the earth did not begin only with my birth, but that it existed long, long before. And I should have the feeling of saying something funny. Rather as if a child had asked if such and such a mountain were higher than a tall house that it had seen. In answering the question I should have to be imparting a picture of the world to the person who asked it.
If I do answer the question with certainty, what gives me this certainty?
 I believe that I have forebears, and that every human being has them. I believe that there are various cities, and, quite generally, in the main facts of geography and history. I believe that the earth is a body on whose surface we move and that it no more suddenly disappears or the like than any other solid body: this table, this house, this tree, etc. If I wanted to doubt the existence of the earth long before my birth, I should have to doubt all sorts of things that stand fast for me.
 And that something stands fast for me is not grounded in my stupidity or credulity.
 If someone said "The earth has not long been..." what would he be impugning? Do I know?
Would it not have to be what is called a scientific belief? Might it not be a mystical one? Is there any absolute necessity for him to be contradicting historical facts? or even geographical ones?
 If