
Denying the Antecedent
Definition:
Any argument of the following form is invalid:
If A then B
Not A
Therefore, Not B
Examples:
 if you get hit by a car when you are six then you will die
young. But you were not hit by a car when you were six.
Thus you will not die young. (Of course, you could be hit by
a train at age seven, in which case you still die young.)
 If I am in Calgary then I am in Alberta. I am not in
Calgary, thus, I am not in Alberta.
Proof:
Show that even though the premises are true, the conclusion
may be false. In particular, show that the consequence B may
occur even though A does not occur.
References
Barker: 69, Cedarblom and Paulsen: 26, Copi and Cohen: 241
26 May 1995
