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.
FIGURE II.
§ 653.
A is B. A is not B.
C is not B. C is B.
.'. C is not A. .'. C is not A.
We establish the distinction between C and A by showing that A has an attribute which C is devoid of, or is devoid of an attribute which C has.
All fishes are cold-blooded.
A whale is not cold-blooded.
.'. A whale is not a fish.
No fishes give milk.
A whale gives milk.
.'. A whale is not a fish.