 The logical relations usually expressed in the Aristotelian square of opposition for assertoric propositions and its modal counterparts become the object of a significant revision in Avicenna’s system, as a result of the richer set of propositions it comprises. Perhaps the most striking feature is the replacement of the Aristotelian assertoric with the one-sided absolute (X1), a proposition containing an implicit temporal modality (“sometimes” or “at least once”) which, unlike the Aristotelian assertoric, is not contradicted by a proposition of the same kind, but by a stronger proposition, namely the “perpetual” (dāʾima) A-proposition.