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Validity

Validity. Validity. All UH students are communists. All communists like broccoli. All UH students like broccoli. Validity. All UH students are communists. All communists like broccoli. GOOD All UH students like broccoli. Validity. All UH students are communists.

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Validity

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  1. Validity

  2. Validity All UH students are communists. All communists like broccoli. All UH students like broccoli.

  3. Validity All UH students are communists. All communists like broccoli. GOOD All UH students like broccoli.

  4. Validity All UH students are communists. All communists like broccoli. GOOD All UH students like broccoli. Logic does not try to decide which statements are true. The issue for logic is: Is the REASONING good?

  5. Validity All UH students are communists. All communists like broccoli. All UH students like broccoli. Premises Conclusion Validity Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F.

  6. Validity and Truth All UH students are communists. All communists like broccoli. All UH students like broccoli. The statements in the argument are FALSE but… The argument is VALID. Valid Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F. False False False

  7. Validity and Truth All canaries have feathers. Some pets have feathers. Some pets are canaries. True True True

  8. Validity and Truth All canaries have feathers. Some pets have feathers. Some pets are canaries. True True True The statements in the argument are TRUE but… The argument is INVALID.

  9. Validity and Truth All canaries have feathers. Some pets have feathers. Some pets are canaries. The statements in the argument are TRUE but… The argument is INVALID. Validity Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F. True True True

  10. Validity and Truth IMAGINE this: Canaries just never ended up being pets; but parrots and mynas are still pets. So it is possible for the premises to be T, and the conclusion F. True All canaries have feathers. Some pets have feathers. Some canaries are pets. True False

  11. Validity and Truth All canaries have feathers. T Some pets have feathers. T Some canaries are pets. T All UH students are communists.F All communists like broccoli. F All UH students like broccoli. F Do Not Ask: Are the statements T? Ask Instead:Assuming the premises are T, must the conclusion be T? Validity Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F.

  12. Validity and Argument Form Logic is the study ofArgument Form not Truth. All Us are Cs. All Cs are Bs. All Us are Bs. All UH students are Communists. F All Communists like Broccoli. F All UH students like Broccoli. F Any argument with this form will be valid, regardless of how false (or silly) its premises may be.

  13. Validity and Argument Form Logic is the study ofArgument Form not truth. All Canaries have Feathers. T Some Pets have Feathers. T Some Canaries are Pets. T All Cs are Fs. Some Ps are Fs. Some Cs are Ps. Any argument with this form will be invalid, regardless of how true its premises may be. Just because all Cs are Fs and some Ps are Fs, It does not follow that some Cs are Ps.

  14. Validity and Argument Form Logic is the study ofArgument Form. All Cs are Fs. Some Ps are Fs. Some Cs are Ps. All Cats have Feet. T Some Pigs have Feet. T Some Cats are Pigs. F Just because all Cs are Fs and some Ps are Fs, It does not follow that some Cs are Ps.

  15. Validity is Different From Truth It is crucial that you distinguish validity from truth. All Cs are Fs. Some Ps are Fs. Some Cs are Ps. All canaries have feathers. T Some pets have feathers. T Some canaries are pets. T

  16. Validity is Different From Truth It is crucial that you distinguish validity from truth. All Cs are Fs. Some Ps are Fs. Some Cs are Ps. All canaries have feathers. T Some pets have feathers. T Some canaries are pets. T INVALID Invalid arguments may have true conclusions.

  17. Validity is Different From Truth It is crucial that you distinguish validity from truth. All Us are Ws. All Ws are B. All Us are B. All UH students are communists. F All communists like broccoli. F All UH students like broccoli. F

  18. Validity is Different From Truth It is crucial that you distinguish validity from truth. All Us are Ws. All Ws are B. All Us are B. All UH students are communists. F All communists like broccoli. F All UH students like broccoli. F VALID Valid arguments may have false conclusions.

  19. Validity is Different From Truth It is crucial that you distinguish validity from truth. The truth values of the statements in an argument do not allow you to predict whether it is valid. With one exception … If the premises are T and the conclusion is F, Then the argument has to be invalid. Valid Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F.

  20. A Common Mistake It is crucial that you distinguish validity from truth. When I ask for the definition of validity, students say: The premises are Tand the conclusion is T. Valid Defined: 1. Assuming the premises are (all) T, the conclusion has to be T. 2. It is impossible for the premises to be T, and the conclusion to be F.

  21. A Common Mistake It is crucial that you distinguish validity from truth. When I ask for the definition of validity, students say: The premises are Tand the conclusion is T. If the premises are Tthen the conclusion must be T. WRONG! RIGHT! For more click here

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