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  1. Graded Structures of Opposition in Fuzzy Natural Logic.Petra Murinová - 2020 - Logica Universalis 14 (4):495-522.
    The main objective of this paper is devoted to two main parts. First, the paper introduces logical interpretations of classical structures of opposition that are constructed as extensions of the square of opposition. Blanché’s hexagon as well as two cubes of opposition proposed by Morreti and pairs Keynes–Johnson will be introduced. The second part of this paper is dedicated to a graded extension of the Aristotle’s square and Peterson’s square of opposition with intermediate quantifiers. These quantifiers are linguistic expressions such (...)
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  • Another Side of Categorical Propositions: The Keynes–Johnson Octagon of Oppositions.Amirouche Moktefi & Fabien Schang - 2023 - History and Philosophy of Logic 44 (4):459-475.
    The aim of this paper is to make sense of the Keynes–Johnson octagon of oppositions. We will discuss Keynes' logical theory, and examine how his view is reflected on this octagon. Then we will show how this structure is to be handled by means of a semantics of partition, thus computing logical relations between matching formulas with a semantic method that combines model theory and Boolean algebra.
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  • Modern Versus Classical Structures of Opposition: A Discussion.Didier Dubois, Henri Prade & Agnès Rico - 2024 - Logica Universalis 18 (1):85-112.
    The aim of this work is to revisit the proposal made by Dag Westerståhl a decade ago when he provided a modern reading of the traditional square of opposition and of related structures. We propose a formalization of this modern view and contrast it with the classical one. We discuss what may be a modern hexagon of opposition and a modern cube, and show their interest in particular for relating quantitative expressions.
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  • Aristotelian and Boolean Properties of the Keynes-Johnson Octagon of Opposition.Lorenz Demey & Hans Smessaert - 2024 - Journal of Philosophical Logic 53 (5):1265-1290.
    Around the turn of the 20th century, Keynes and Johnson extended the well-known square of opposition to an octagon of opposition, in order to account for subject negation (e.g., statements like ‘all non-S are P’). The main goal of this paper is to study the logical properties of the Keynes-Johnson (KJ) octagons of opposition. In particular, we will discuss three concrete examples of KJ octagons: the original one for subject-negation, a contemporary one from knowledge representation, and a third one (hitherto (...)
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  • The Cretan Square.Jean-Yves Beziau & Jens Lemanski - 2020 - Logica Universalis 14 (1):1-5.
    This special issue is related to the 6th World Congress on the Square of Opposition which took place at the Orthodox Academy of Crete in November 2018. In this introductory paper we explain the context of the event and the topics discussed.
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