Document Type : Letter to Editor
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Abstract
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We know for logic two systems: the Ancient Logic and the Modern Logic, which are inconsistent in some points of view. In this paper, I want to see if Ancient Logic, versus Modern Logic, is really one logic, has one set of rules, and introduces one methodology. There are many disagreements on the number and the exact formulation of the valid rules of Ancient Predicate Logic. For instance, the various formulations of the Obversion and Contraposition (the congruent and the opposite) can be mentioned as evidence for the claim. Since Aristotle has not spoken of contraposition, it can be concluded that adding the two forms of contraposition to his logical rules provide us with two new logical systems, in which the formulations of the quantified propositions differ from that in Aristotle’s system. Also, since there have appeared different theories on Congruent Contraposition and the Obvertion between Muslim logicians, the number of the systems has reached the six. In this paper, introducing an exact definition for each of these systems, I present suitable formulations for the quantified propositions at the mentioned six systems.
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