Lecture #2 - Philosophy 12A Lecture #2 1/21/10 Sections...

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Philosophy 12A Lecture #2 1/21/10 Sections next week in 301 Moses unless e-mailed differently Review from Lecture #1 The basic units of logical analysis are propositions Propositions have their truth values objectively, assuming true and false eternally Truth and falsity = actual truth and falsity When said true or false, it is shown in the point of view of the actual world There are conceivable worlds where “Al Gore is President in 2007” so possibly true, which is the main interest in logic Some propositions are not even possibly true, like 2 + 2 = 5 Branden weighs 200 lbs and Branden does not weigh 200 lbs is not possible in any worlds, making it logically impossible Impossibility is the key to logic, not conditional on anything All true/false questions mean ACTUAL true or false not possible true or false If Branden is a good man, then Branden is a man is actually true, but (logically) necessarily true Arguments, Following-From, and Validity An argument is a collection of propositions, one of which (the conclusion) is supposed to follow from the rest (the premises) If the conclusion of an argument follows from its premises, then the argument is said to be valid
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Lecture #2 - Philosophy 12A Lecture #2 1/21/10 Sections...

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