Thursday, July 31, 2008

Logic I, Lesson 2: Univocal, Equivocal, & Analogical Terms


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From Aristotle's Categories 1:

Things are said to be named 'equivocally' when, though they have a common name, the definition corresponding with the name differs for each. Thus, a real man and a figure in a picture can both lay claim to the name 'animal'; yet these are equivocally so named, for, though they have a common name, the definition corresponding with the name differs for each. For should any one define in what sense each is an animal, his definition in the one case will be appropriate to that case only.

On the other hand, things are said to be named 'univocally' which have both the name and the definition answering to the name in common. A man and an ox are both 'animal', and these are univocally so named, inasmuch as not only the name, but also the definition, is the same in both cases: for if a man should state in what sense each is an animal, the statement in the one case would be identical with that in the other.


From Ralph McInerny's Aquinas & Analogy, p. 96:

Things are to be named analogously when, though they have a name in common, the definitions corresponding with the name are partly the same and partly different, with one of those definitions being prior to the others... "For example, 'healthy' as said of urine signifies a sign of the health of the animal, but said of medicine it signifies the cause of the same health" [St. Thomas, Summa Theologiae I.15.5c].


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