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lecture3 - Recap An argument is valid if and only if its...

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    Recap An argument is valid if and only if it’s necessary that if the premises are true, then the conclusion is true. An argument is sound if and only if it is valid and has all true premises. An argument is strong if and only if it’s probable (but not necessary ) that its conclusion is true, given that its premises are true.
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    Some types of strong argument Arguments from authority. 1) According to the Philosophy Department website, philosophy majors are required to take Phil 3 or Phil 183 So, 2) Philosophy majors are required to take Phil 3 or Phil 183 This is a strong argument because the Philosophy Department website is a reliable source concerning the requirements for Philosophy majors. Arguments from authority have the following form: 1) R is a reliable source concerning S 2) R said that S So, 3) S It’s likely that the conclusion is true, on the assumption that the premises are.
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    Arguments by analogy Example: 1) Jack’s horse is similar to Jill’s horse in size, strength, speed and training. 2) Jill’s horse can jump the fence. So, 3) Jack’s horse can jump the fence. If the premises are true, it’s likely that the conclusion is true too. Arguments by analogy have the following form: 1) A is similar to B is certain respects 2) B has property P So, 3) A has property P Note that such arguments are only strong if A is similar to B in relevant ways. Compare: 1) Tom’s horse is similar to Tara’s horse in being the same color and having the same birthday. 2) Tara’s horse can jump the fence So, 3) Tom’s horse can jump the fence
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    Cogency An argument is cogent if and only if: (i) it is strong , and (ii) all of its premises are true.
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