Abstract

The article investigates the treatment of modality in chapters 12 and 13 of De Interpretatione and gives a new interpretation of the puzzling table of modals to be found at the beginning of chapter 13, as well as dealing with some of Aristotle’s puzzles. This is achieved by extending Aristotle’s distinction between two senses of possibility, which (following Ackrill) I call ‘one-sided’ and ‘two-sided’, to the two notions of necessity and impossibility. The conclusion is reached that, while the two notions of necessity and impossibility are logically incompatible when both are taken as one-sided, in their two-sided senses they are in fact equivalent.