An event in the history of analytic philosophy: the square of opposition replaced by the logical hexagon of Robert Blanché (original) (raw)

In On Interpretation, Chapter 7, Aristotle alters a system of three pairs of natural mutually contradictory propositions, in that he eliminates the pair where two natural universals Men are white and Men are not white oppose each other contradictorily (see the diagram I above). This alteration has serious consequences : the two natural pairs, which Aristotle considers exclusively: All men are white versus Some men are not white and Some men are white versus No man is white are illegitimately identified with the two pairs of logical contradictories constituting the logical square: A versus O and I versus E respectively