Two propositions with the same subject and predicate terms that agree in…

Concept

In the traditional square of opposition, categorical propositions are classified by quantity (universal or particular) and quality (affirmative or negative).

A relation is identified by comparing which of these two features remains the same and which one changes between propositions with the same subject and predicate terms.

Application

Here the quality remains the same, but the quantity changes from universal to particular. This gives the A–I affirmative pair or the E–O negative pair, which are corresponding propositions.

Contrast

• Contraries: A and E are both universal, while their quality differs.

• Sub-contraries: I and O are both particular, while their quality differs.

• Contradictory pairs: A–O and E–I differ in both quantity and quality.

• Corresponding pairs: A–I and E–O keep the same quality and differ only in quantity.

Cross-check

“All S are P” and “Some S are P” are both affirmative but differ in quantity; likewise, “No S are P” and “Some S are not P” are both negative but differ in quantity. Both checks yield the corresponding relation.

Result

Therefore, the propositions are known as corresponding propositions.