Either wages fall, or the weaker hands are dismissed;

Wages do not fall:
∴ The weaker hands are dismissed.

But we cannot argue—

Wages fall:
∴ The weaker hands are not dismissed;

since in 'hard times' both events may happen together.

Rule of the Modus tollendo ponens: If one alternative be denied, the other is affirmed.

When, however, the alternatives of the Disjunctive are mutually exclusive, we have also the

Modus ponendo tollens.
EitherA is B, or C is D;
A is B (or C is D):
∴C is not D (or A is not B).

Either the Tories or the Whigs win the election;