Note 317 — Chapter I

Lotze (Logic, § 89; Outlines of Logic, §§ 40-42) holds that two negative premisses invalidate a syllogism in figure 1 or figure 2, but not necessarily in figure 3. The example upon which he relies is this,—No M is P, No M is S, therefore, Some not-S is not P. The argument in the text may be applied to this example as well as to the one given by Jevons.