Introductory Logic
Quiz #2
September 16, 2005
 

Name______________________
R. Hammack
Score _________
DIRECTIONS. Two deductive arguments are given. For each one, say if it's valid or invalid, and sound or unsound. If it's invalid, prove this using the counterexample method.

(1) If animal species are fixed and immutable, then evolution is a myth. Therefore, evolution is not a myth, since animal species are not fixed and immutable.

Let:
A = "Animal speies are fixed and immutable"
E = "Evolution is a myth"

Then the argument form is:

If A then E.
It's not true that A.
Therefore it's not true that E.

Now put in the following substitutions.
A = "George Washington was murdered"
E = "George Washington died"

Then the argument becomes:

If George Washington was murdered then George Washington died.
It's not true that George Washington was murdered.
Therefore it's not true that George Washington died.

This has true premises and false conclusion, so the argument is INVALID.


(2) The Theory of Evolution is correct, since George Bush says it's true, and he's never wrong about anything.

The argument is:

George Bush says the Theory of Evolution is true.
George Bush is never wrong about anything.
Therefore the Theory of Evolution is correct.

This is VALID, because if the premises are true, then the conclusion is necessarily true.
However, at least one premise if false, namely the second one: George Bush was wrong about there being WMD's in Iraq.
Thefore the argument is UNSOUND.