PHIL 130g Lecture Notes - Lecture 5: If And Only If, Logical Form, Soundness
Document Summary
Arguments (continued: validity and soundness (continued, recall from last class that: Recall from last class that this logical form is called modus ponens. If an argument is sound, we know its conclusion is true. Recall from last class that this, too, is an instance of modus ponens. Both of the premises in this second argument are false, but it is still just as valid as the: p q, ~q p, ~q, so, p. To find out, we begin by asking if there is any way the premises could both be true while the conclusion is false. Socrates is still mortal if he"s a turtle. We call this argument form denying the antecedent, and it is a logical fallacy: if socrates is human, then socrates is mortal, socrates is mortal, so, socrates is human, q, so, p, p q. No, because both premises could be true and the conclusion could still be false. For example, again, socrates could be a turtle.
