Square of Opposition:
Contraries

An A proposition and an E proposition that have the same subject and predicate terms cannot both be true, but they could both be false. We identify this relationship in logic by calling A and E contrary propositions. "All S is P" and "No S is P" are contraries.

Example:

"All bread is nutritious" and "No bread is nutritious" are opposing statements. They cannot both be true. However, they could both be false. If some types of bread are nutritious and others are not, then both statements would be false.

Contraries | Contradictories |
Subalternates | Subcontraries


Square of Opposition

© Copyright 1998, W.W. Norton & Co.