337. One cannot make experiments if there
are not some things that one does not doubt. But that does not mean that one
takes certain presuppositions on trust. When I write a letter and post it, I
take it for granted that it will arrive – I expect this.
If I make an experiment I do not doubt the
existence of the apparatus before my eyes. I have plenty of doubts, but not that. If I do a calculation I believe,
without any doubts, that the figures on the paper aren’t switching of their own
accord, and I also trust my memory the whole time, and trust it without
reservation. The certainty here is the same as my never having been on the
moon.
yes we operate with expectation –
and the ground of expectation is
uncertainty
I make assumptions when I experiment or calculate
–
and the ground of assumption is uncertainty
the fact that propositional reality is
uncertain –
does not stop me operating
that I have never been on the
moon –
is a proposition I would assent to
but if you say the proposition is certain –
in what does the certainty consist?
the fact is –
once this question is asked –
any supposed certainty –
disappears
