Deductive Logic

by St. George William Joseph Stock

FIGURE 1.

§ 652.

B is or is not A.
C is B.
.'. C is or is not A.

We prove that C has or has not the property A by predicating of it B, which we know to possess or not to possess that property.

Luminous objects are material.
Comets are luminous.
.'. Comets are material.

No moths are butterflies.
The Death's head is a moth.
.'. The Death's head is not a butterfly.