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Aristotle (384–322 BCE)

Aristotle 's main contribution to rationalist thinking was the use of syllogistic logic and its use in argument. Aristotle defines syllogism as "a discourse in which certain (specific) things having been supposed, something different from the things supposed results of necessity because these things are so." Despite this very general definition, Aristotle limits himself to categorical syllogisms which consist of three categorical propositions in his work Prior Analytics. These included categorical modal syllogisms.