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lecture17 - Lecture 17 Syllogisms in Ordinary Language...

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Lecture 17 Syllogisms in Ordinary Language Patrick Maher Philosophy 102 Spring 2009
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Introduction The arguments that people give in ordinary language are rarely expressed as categorical syllogisms in standard form. However, it is often possible to rephrase arguments that occur in ordinary language so they become syllogisms in standard form. Today we will learn techniques for doing that.
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Reducing the number of terms Categorical syllogisms in standard form contain three terms. If an argument contains more, the number of terms must be reduced. Example All photographers are non-writers. Some editors are writers. Therefore, some non-photographers are not non-editors. Symbolized: All P are non- W . Some E are W . Some non- P are not non- E . Reduced: No P are W . (obversion) Some E are W . Some E are not P . (contraposition) Valid
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Review of allowed operations Conversion is allowed for E and I propositions. (I.e., when the terms are distributed alike.) Contraposition is allowed for A and O.
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