Note 367 — Chapter III
Reading edition
Sigwart’s way of putting it (Logic, i. p. 354) is that in figure 2, instead of inferring from ground to consequence, we infer from invalidity of consequence to invalidity of ground; and he gives the following scheme:
If anything is P it is M (or is not M),
Certain subjects S are not M (or are M),
therefore, They are not P.