How to Win Every Argument: The Use and Abuse of Logic (2006)

50 How to Win Every Argument

slow.' The first of these is a type of argument called the modus
ponens, the second is called the modus tollens, and both are valid.
It is the other two which are fallacies, even though they resemble
the valid forms.
Denying the antecedent is a fallacy because it assigns only one
cause to an event for which there might be several. It dismisses
other possibilities which could occur.
The fallacy commonly occurs where plans are being laid. It
engenders the belief that if those things are avoided which bring
harmful consequences, then a pleasant outcome can be
expected:

If I smoke, drink or have sex, it will shorten my life-span. I shall give up

cigars, booze and women and live another hundred years.

(No. It will just feel like a hundred years.)

It occurs to no lesser degree on the international scale. Countries
may calculate the courses of action which bring unpleasant
consequences in their wake. What they are not able to do is
insure themselves against even worse outcomes simply by
avoiding those actions.

If we have a strong army, countries which fear it might attack us. So by

disarming, we remove that risk.

(Possibly, but they might be more likely to attack because it brings no

retaliation.)

You can use the fallacy of denying the antecedent very skilfully
in support of the status quo. It is a natural conservative fallacy
because most changes we make do not avert all of the evils of the
world. By pointing to the likelihood that death and taxes will be
the result of the proposed actions, you might lull an audience