[Revised entry by Terence Parsons and Graziana Ciola on May 19, 2025.
Changes to: Main text, Bibliography, notes.html]
This entry traces the historical development of the Square of Opposition, a collection of logical relationships traditionally embodied in a square diagram. This body of doctrine provided a foundation for work in logic for over two millennia. For most of this history, logicians assumed that negative particular propositions (“Some S is not P”) are vacuously true if their subjects are empty. This validates the logical laws embodied in the diagram, and preserves the doctrine against modern criticisms….

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