Philosophy Homework Worksheet (Page 4 of 4) in pdf

Philosophy Homework Worksheet Page 4

• Let P = today is Tuesday and Q = today is Thursday. Then (if today is, in fact, Tuesday) the

premise is true, but the conclusion is false. So, there are instances of this argument (form) that

have true premises and a false conclusion. So, this argument (form) must be invalid.

29. The following argument is valid (absolutely): “Pete Sampras is a professional football player. If

Pete Sampras is a professional football player, then Pete Sampras is bald. Therefore, Pete Sampras

is bald.”

• This argument is sententially valid (modus ponens). So, it is valid “absolutely”.

30. The following argument is sound (absolutely): “If Prince William is unmarried, then Prince

William is a bachelor. Prince William is a bachelor. Therefore, Prince William is unmarried.”

• I originally wrote this one (years ago) before Prince William got married. Given that he is now

married, it is easy to see that this argument is unsound (it’s second premise is false). But, even if

Prince William were still unmarried, the argument would (still) not be sound. This is because it

is not sententially valid (its sentential form is aﬃrming the consequent), and it is not something

we’re going to call “absolutely” valid either, since one would need to know the meanings of

“unmarried” and “bachelor” to rule-out counterexamples to its validity (i.e., cases in which its

second premise is true but its conclusion is false).

Philosophy Homework Worksheet Page 4