Validity Part 1 - Todays Topics (9/28) I. Two Ways that a...

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3/4/11 Today’s Topics (9/28) I. Two Ways that a Conclusion can Follow From a Set of Premises II. Valid Arguments a) A Test for Validity b) Validity and Form III. Invalid Arguments IV. Valid vs. Invalid Arguments a) Valid & Invalid Arguments: True Premises, True Conclusion
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3/4/11 I. Two Ways that a Conclusion Can Follow THE STRONG SENSE EXAMPLE: 1. All ravens are black. ∴ 2. If there is a raven on top of Pikes Peak, then the raven is black. If the premises of the argument were true, the conclusion would have to be true. THE WEAKER SENSE EXAMPLE: 1. All ravens that have been observed so far are black. ∴ 2. If there is a raven on top of Pikes Peak, then the raven is black. If the premises of the argument were true, the conclusion would probably be true.
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3/4/11 II. Valid Arguments An argument is valid if and only if it is impossible for the premises to be true and the conclusion false. VALID EXAMPLE: 1. All ravens are black. ∴ 2. If there is a raven on top of Pikes Peak, then the raven is black. This argument is valid because it is impossible for the premises to be true and the conclusion false. INVALID EXAMPLE: 1. All ravens that have been observed so far are black. ∴ 2. If there is a raven on top of Pikes Peak, then the raven is black. This argument is invalid because it is possible for the premises to be true and the conclusion false.
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3/4/11 II. a) A Test for Validity EXAMPLE : 1. Babe Ruth is the president of the United States. 2.
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Validity Part 1 - Todays Topics (9/28) I. Two Ways that a...

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