1-27-11

1-27-11 - 1-27-11 Evaluating Arguments (Terminology) o...

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Unformatted text preview: 1-27-11 Evaluating Arguments (Terminology) o Deductive arguments o Valid o Invalid o Sound o Unsound o Propositions o True o False o Probably/ improbable o Possible/ impossible Example of a Valid Argument 1) If my car runs, then my car has gas 2) My Car runs C) Therefore, my car has gas Example of an Invalid Argument 1) If my car runs, then my car has gas 2) My car has gas C) Therefore, my car runs Deductive Validity o An argument is deductively valid if and only if it is impossible for all of the premises to be true and for conclusion to be false o An argument is deductively valid if and only if the conclusion is true if all of the premises are true Judging Validity o We judge validity by attempting to imagine scenarios where all of the premises are true but where the conclusion is false Test Case 1) Birds swim and fish fly C) Birds swim Test Case 1) If you don’t study today, you wont study tomorrow 2) If you don’t study tomorrow, you wont study ever again C) Therefore, if you don’t study today, you wont study ever again Test Case 1) All dogs are mammals 2) McCloud is a mammal C) Therefore, McCloud is a dog Test Case 1) Nobody likes ice cream 2) All ice cream is dairy C) Nobody likes dairy Test Case 1) Dragons are fictional 2) Dragons are not fictional C) Therefore, unicorns are dangerous Bad argument/impossible for both premises to be true/Valid – when premises contradict each other, the argument is valid Questions o Can a valid argument have a false conclusion? T o Can a valid argument have all false premises? T o Can a valid argument have a false premises and a true conclusion? T o Can a valid argument have some premises as true and other premises as false? T ...
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This note was uploaded on 04/05/2012 for the course PHI 2100 taught by Professor Mikepatterson during the Spring '12 term at FSU.

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1-27-11 - 1-27-11 Evaluating Arguments (Terminology) o...

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