contraries

In traditional logic, contraries and contradictories describe different types of opposition between statements.

Contraries are two universal statements with the same subject and predicate, where one is an affirmation and the other a denial. For example, "Every S is P" and "No S is P." Contraries can both be false but cannot both be true.1

Contradictories are statements opposed in both quantity (universal vs. particular) and quality (affirmation vs. denial). For instance, "Every S is P" and "Some S is not P" are contradictories. One contradictory statement is true if and only if the other is false.1

Aristotle's work, particularly the Organon, laid the foundation for the systematic study of logic, including these concepts of proposition opposition.2