Truth and Validity

  1. "All radicals are anti-corporate and Marta is a radical. So Marta is anti-corporate"
  2. "All softmicro products are junk and FrontSheet is a softmicro product, so FrontSheet is junk."

These are arguments. Arguments consist of premises and a conclusion.

Questions: 1) What are the premises of (a)? What is the conclusion?

2) What are the premises of (b)? What is the conclusion?

The premises are supposed to prove the conclusion.

  1. Do they in (a)?
  2. Do they in (b)?

A valid argument form is one which, given true premises, guarantees a true conclusion.

An invalid argument form cannot guarantee a true conclusion if given true premises.

  1. Alex is a man, and he's a good driver. All men are good drivers!

Is this valid? Does it have valid form? A hint that it does not is that the conclusion is wrong! If you find a conclusion that's wrong, the argument either has flawed premises or an invalid form.

5) Which is the case for (c)?

A conclusion is not necessarily wrong because it comes from an invalid argument. The argument just doesn't prove the conclusion. Consider:

d. Birds have eyes. Animals have eyes. Therefore, birds are animals.

The conclusion is true, but it doesn't follow from the premises. What about this argument, a favorite in the 1950s:

e. All liberals are communists. Rosa is a liberal. Rosa is a communist!

6) Is (e) valid? (Does it have a valid form? If it were true that all liberals were communists and Rosa was liberal, would it also be true that Rosa was communist?)

7) Is (e) true? If not, what is wrong with it? (Hint: remember the two ways an argument can fail)


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