Lecture #3 - Philosophy 12A Lecture #3 Our Two Renditions...

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Philosophy 12A Lecture #3 1/26/10 Our Two Renditions of Validity – Are they equivalent? An argument is valid if and only if it is logically necessary that if all the premises of the argument are true, then the conclusion of the argument is true An argument is valid if and only if it is logically impossible that both all the premises of the argument are true and the conclusion is false (official definition) Logical Form I We are adopting the following “conservative” heuristic in this course o We will conclude that the argument is valid if and only if we have identified the argument as having a valid logical form – according to one of our theories of valid logical form Logical Form II The sentential form of an argument (or, the sentences faithfully expressing an argument) is obtained by replacing each basic (or, atomic) sentence in the argument with a single (lower-case) letter. A basic sentence is a sentence that doesn’t contain any sentences as a proper part o Branden is a philosopher and Branden is a man. [p and q]
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Lecture #3 - Philosophy 12A Lecture #3 Our Two Renditions...

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