Truth and
Validity
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.
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.
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)