- Polysyllogism
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Not to be confused with Polylogism.
A polysyllogism (also called multi-premise syllogism, sorites, climax, or gradatio) is a string of any number of propositions forming together a sequence of syllogisms such that the conclusion of each syllogism, together with the next proposition, is a premise for the next, and so on. Each constituent syllogism is called a prosyllogism except the very last, because the conclusion of the last syllogism is not a premise for another syllogism. For example:
- It is raining.
- If we go out while it is raining we will get wet.
- If we get wet, we will get cold.
- Therefore, if we go out we will get cold.
Examination of the structure of the argument reveals the following sequence of constituent (pro)syllogisms:
- It is raining.
- If we go out while it is raining we will get wet.
- Therefore, if we go out we will get wet.
- If we go out we will get wet.
- If we get wet, we will get cold.
- Therefore, if we go out we will get cold.
A sorites is a specific kind of polysyllogism in which the predicate of each proposition is the subject of the next premise. Example:
- All lions are big cats.
- All big cats are predators.
- All predators are carnivores.
- Therefore, all lions are carnivores.
The word "sorites" ( /sɒˈraɪtiːz/) comes from Ancient Greek: σωρίτης "the fallacy of the heap", from σωρός "heap" or "pile". In other words, a sorites is a heap of propositions chained together.
Lewis Carroll uses sorites in his book Symbolic Logic. Here is an example [1]:
- No experienced person is incompetent;
- Jenkins is always blundering;
- No competent person is always blundering.
- ∴ Jenkins is inexperienced.
Carroll's example may be translated thus
- All experienced persons are competent persons.
- No competent persons are blunderers.
- Jenkins is a blunderer.
- ∴ Jenkins is not an experienced person.
References
- B. P. Bairan. An Introduction to Syllogistic Logic. Goodwill Trading. p. 342. ISBN 9715740944.
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