Around and Beyond the Square of Opposition

Part of the series Studies in Universal Logic pp 21-40

Logical Oppositions in Arabic Logic: Avicenna and Averroes

  • Saloua ChattiAffiliated withDepartment of Philosophy, Faculté des Sciences Humaines et Sociales, University of Tunis Email author 

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In this paper, I examine Avicenna’s and Averroes’ theories of opposition and compare them with Aristotle’s. I will show that although they are close to Aristotle in many aspects, their analysis of logical oppositions differs from Aristotle’s by its semantic character, and their conceptions of opposition are different from each other and from Aristotle’s conception. Following Al Fārābī, they distinguish between propositions by means of what they call their “matter” modalities, which are determined by the meanings of the propositions. This consideration gives rise to a precise distribution of truth-values for each kind of proposition, and leads in turn to the definitions of the logical oppositions. Avicenna admits the four traditional oppositions, while Averroes, who seems closer to Aristotle and especially to Al Fārābī, does not mention subalternation, but admits subcontrariety. Nevertheless, we can find that Averroes defends what Parsons calls SQUARE and [SQUARE], because he holds E and I-conversions and the truth conditions he admits are just those that make all the relations of the square valid, while Avicenna defends SQUARE and [SQUARE] only for the waṣfī reading of assertoric propositions. They also give a special attention to the indefinite which in Averroes’ view is ambiguous, while Avicenna treats it as a particular. Some points of their analysis prefigure the medieval concepts and distinctions, but their opinion about existential import is not as clear as the medieval one and does not really escape the modern criticisms.


Logical oppositions Matter necessity Possibility and impossibility Existential import Indefinites waṣfī vs ḍātī readings of propositions

Mathematics Subject Classification

03A05 03B10