fact expressed

If it both rains and blows a pear is ripe.

[Go to Vol 2 p 40 (MS 456)]

We now have three tules of necessary inference.
First, from any premiss A, we can necessarily
conclude B, if and only if we know that it
is not the case that A is true while B is false.

We may, therefore, rub out everything on
the board, because we know that the blank
sheet of assertion asserts nothing false. Hence
if two graphs are written one may erase either
of them, because each has the same signification
as if it stood alone, and either standing alone
might be erased.

But now if any graph, G, could if it were scribed on the
sheet of assertion be transformed into another
graph H without fear of introducing falsity

Page Notes

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Peirce's instruction to "Go to Vol 2 p 40" refers to the beginning of MS 456. From this point on p. 15 to the middle of Peirce's p. 18 (including some unnumbered pages) seems to be an earlier draft that was superseded by MS 456. Then the final part of the lecture begins on p. 18 of this MS (455).