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Validity and Soundness

Validity and Soundness. Evaluating philosophical argument. Validity. Important tool to evaluate a deductive argument. Validity. Validity. What is an argument ? A set of statements, one or more of which is offered in support of some statements Premises Statement doing the supporting

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Validity and Soundness

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  1. Validity and Soundness Evaluating philosophical argument

  2. Validity Important tool to evaluate a deductive argument Validity

  3. Validity What is an argument? A set of statements, one or more of which is offered in support of some statements Premises Statement doing the supporting Conclusion The statement being supported Philosophical notion of Validity (Review)

  4. Text Deductive arguments An argument is valid or invalid What is a valid argument? P1: All humans are mortal P2: Socrates is human C: Therefore, Socrates is mortal Philosophical notion of Validity The argument is good? All the premises and conclusion are true?

  5. Validity Deductive arguments An argument is valid or invalid Validity has nothing to do with truth of the conclusion Or how good the conclusion is Philosophical notion of Validity

  6. Validity An argument is valid If and only if the truth of its premises guarantees the truth of its conclusion Validity is a property of arguments such that if the premises of the arguments are true, then the conclusion must be true Validity of an Argument

  7. Validity It’s impossible for a valid argument to have all true premises unless the conclusion is also true The premises entails the conclusion

  8. So…. Argument can be

  9. Validity If an argument is valid, then if its premises are true then the conclusion is true If an argument is valid, then the truth of its conclusion follows from the truth of its premises Argument VALIDITY is conditional

  10. Validity DUDE this is soooo abstract….

  11. Validity This is a valid argument P1: All humans are mortal P2: Socrates is human C: Therefore Socrates is mortal Remember, if the premises of this argument are true, then the conclusion must be true in this case Some examples… True True True

  12. Validity This is a valid argument - With all false premises P1: All humans are immortal P2: Socrates is human C: Therefore Socrates is immortal ** It doesn’t matter if the premises are true or false! Some examples… If True If True Necessarily true

  13. Validity This is a valid argument - With premises of which we don’t know the truth P1: All alliens speak English P2: Splock is an Alien C: Therefore, Splock speaks English Premisses could be true or false Some examples… If True If True Necessarily true

  14. Validity It’s impossible for all the premises to be true while the conclusion is false Summary - Valid Argument

  15. Validity The truth of the argument’s premises does not entail the truth of the conclusion…. P1: All dogs have fur P2: Claire has a lot of fur C: Therefore, Claire is a dog The truth of this conclusion doesn’t follow from the premises because Cats also have a lot of fur. Invalid Argument If True If True Could be false

  16. Validity Why validity matters if the truth of the premises doesn’t matter? • Validity determines whether an argument obeys logic/valid inference rules.

  17. Validity Now, write 3 examples of a valid or invalid argument of your own. Share and discuss with a partner

  18. Soundness

  19. Soundness Soundness of an argument requires: 1. The argument must be valid Conclusion cannot be false if the premises are true 2. The premises must all be true

  20. Soundness Example -

  21. Soundness Example -

  22. Validity Now, write 3 examples of a sound argument of your own. Share and discuss with a partner

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