### Immediate Inference:Obversion

When we group things together into a class, we are distinguishing them from everything else. For every class C, there is a complementary class composed of everything else, everything not included in C. This is called the complement of C, and it is usually labeled "non-C." Thus the complement of "abrasive things" is "nonabrasive things."

We arrive at the obverse of a proposition by making two changes:

1. Replace the predicate term with its complement

2. Change the quality of the proposition (affirmative to negative or negative to affirmative)

 Example: STANDARD PROPOSITION OBVERT All S is P No S is non-P All sandpaper is abrasive. No sandpaper is nonabrasive. No S is P All S are non-P No machine is conscious. All machines are nonconscious. Some S are P Some S are not non-P Some people are kind. Some people are not unkind. Some S are not P Some S are non-P Some chemicals are not toxic. Some chemicals are nontoxic.

Conversion | Obversion | Contraposition

Immediate Inference