seems to be fixed, and it is removed from the traffic. It is also so to speak shunted onto an unused siding.
 Now it gives our way of looking at things, and our researches, their form. Perhaps it was once disputed. But perhaps, for unthinkable ages, it has belonged to the scaffolding of our thoughts. (Every human being has parents.)
 In certain circumstances, for example, we regard a calculation as sufficiently checked. What gives us a right to do so? Experience? May that not have deceived us? Somewhere we must be finished with justification, and then there remains the proposition that this is how we calculate.
 Our 'empirical propositions' do not form a homogeneous mass.
 What prevents me from supposing that this table either vanishes or alters its shape and colour when on one is observing it, and then when someone looks at it again changes back to its old condition? - "But who is going to suppose such a thing?" - one would feel like saying.
 Here we see that the idea of 'agreement with reality' does not have any clear application.
 The proposition "It is written".
 If someone supposed that all our calculations were uncertain and that we could rely on none of them (justifying himself by saying that mistakes are always possible) perhaps we would say he was crazy. But can we say he is in error? Does he not just react differently? We rely on calculations, he doesn't; we are sure, he isn't.
 Can I believe for one moment that I have ever been in the stratosphere? No. So do I know the contrary, like Moore?
 There cannot be any doubt about it for me as a reasonable person. - That's it. -
 The reasonable man does not have certain doubts.
 Can I be in doubt at will?
 I cannot possibly doubt that I was never in the stratosphere. Does that make me know it? Does it make it true?
 For mightn't I be crazy and not doubting what I absolutely ought to doubt?
 "I know that it never happened, for if it had happened I could not possibly have forgotten it."
But, supposing it did happen, then it just would have been the case that you had forgotten it. And how do you know that you could not possibly have forgotten it? Isn't that just from earlier experience?
 What I hold fast to is not one proposition but a nest of propositions.
 Can I give the supposition that I have ever been on the moon any serious consideration