- square of opposition
- In traditional logic the square of opposition summarizes the logical relationships between the four forms of subject-predicate proposition known as A, E, I, O: All X are Y; no X are Y; some X are Y; some X are not Y. In the diagram, contradictories are propositions that cannot both be true and cannot both be false. Contraries cannot both be true, but can both be false. A proposition is subaltern to another if it is implied by it, but does not imply it. Subcontraries can both be true, but cannot both be false. The relations as indicated depend upon reading existential import into, for example, ‘All X are Y’. In modern quantification theory the generalization carries no implication that there are any things that are X, and indeed, is bound to be true when there are none (see vacuous ).
Philosophy dictionary. Academic. 2011.
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Square of opposition — In the system of Aristotelian logic , the square of opposition is a diagram representing the different ways in which each of the four propositions of the system are logically related ( opposed ) to each of the others. The system is also useful in … Wikipedia
square of opposition — a square figure on which may be demonstrated the four logical oppositons by contrariety, subcontrariety, subalternation, and contradiction * * * Logic. a diagrammatic representation of the opposition of categorical propositions. [1860 65] … Useful english dictionary
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