Logic is the study of correct reasoning. A host of philosophical themes have clustered around this central concern: the nature of truth and validity, of possibility and necessity; the semantics of words, sentences, and arguments; and even questions about substances and accidents, free will and determinism.
Syllogisms (in the narrow sense considered in the Prior Analytics) consist of three assertoric sentences, two of them premises, from which the third, the conclusion, follows. In an assertoric sentence, something is "predicated" of a subject, and a predicate can stand in one of just five relations to a subject: it may be its definition, its genus ("Man is an animal"), it…
In the twelfth century, the logica vetus was the central concern of the flourishing Paris schools. Peter Abelard (1079–1142), the greatest logician of the time, developed a nominalist metaphysics on its basis and elaborated a semantics to explain how sentences that use universal words (such as "Socrates is a man") are meaningful although there are no universal things, only par…
From the middle of the twelfth century, logicians developed various branches of their subject, known as the logica modernorum ("contemporary logic"), that had not been treated specially, or at all, in antiquity. Peter of Spain's widely read Tractatus (often called Summulae logicales) illustrates how parts of the logica modernorum had developed up until about the 1230s. There w…
Logic was no less important for Islamic than for Christian philosophers and theologians. By the time of al-Farabi (c. 878–950), the first important Islamic logician, the whole of Aristotle's logical Organon was available in Arabic—far more material, then, than in the Latin West at this period, especially since the Arabic logicians tended to follow the habit of late antiquity i…
Aristotle. The Complete Works of Aristotle. Edited by Jonathan Barnes. Vol. 1. Princeton, N.J.: Princeton University Press, 1984. ——. Prior Analytics. Translated by Robin Smith. Indianapolis: Hackett, 1989. Kretzmann, Norman, and Eleonore Stump, eds. Logic and the Philosophy of Language. Vol. 1 of The Cambridge Translations of Medieval Philosophical Texts. Cambridge, U.K.: Cambridge …
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