  In “The Critique of the Logical Principle of the Excluded Middle” (1913) Leśniewski distinguishes between an ontological principle – Every object is either \(A\) or not \(A\) – and a logical principle – Of two contradictory propositions, at least one must be true. He rejects the latter because he takes ‘Every centaur has a tail’ and ‘Some centaur does not have a tail’ to be contradictories, but both to be false because the subject-term ‘centaur’ is empty. This clearly depends on a reading of the universal with existential import. If instead for the universal we take ‘Any centaur has a tail’, which is true if there are no centaurs, then we do get a contradictory pair with opposite truth-values.