Also called Scare Tactics, Ad Baculum.
The reader is told that unpleasant consequences will follow if they do not agree with the author. The fallacy has the following pattern:
This line of "reasoning" is fallacious because creating fear in people does not constitute evidence for a claim. It is important to distinguish between a rational reason to believe (RRB) (evidence) and a prudential reason to believe (PRB) (motivation). A RRB is evidence that objectively and logically supports the claim. A PRB is a reason to accept the belief because of some external factor (such as fear, a threat, or a benefit or harm that may stem from the belief) that is relevant to what a person values but is not relevant to the truth or falsity of the claim. For example, it might be prudent to not fail the son of your department chairperson because you fear he will make life tough for you. However, this does not provide evidence for the claim that the son deserves to pass the class.
"You know, Professor Smith, I really need to get an A in this class. I'd like to stop by during your office hours later to discuss my grade. I'll be in your building anyways, visiting my father. He's your dean, by the way. I'll see you later."
"I don't think a Red Ryder BB rifle would make a good present for you. They are very dangerous and you'll put your eye out. Now, don't you agree that you should think of another gift idea?"
You must believe that God exists. After all, if you do not accept the existence of God, then you will face the horrors of hell."
"You shouldn't say such things against multiculturalism! If the chair heard what you were saying, you would never receive tenure. So, you had just better learn to accept that it is simply wrong to speak out against it."
You had better agree that the new company policy is the best bet if you expect to keep your job.
NAFTA is wrong, and if you don't vote against NAFTA then we will vote you out of office.
Can be efficient if your threat is credible enough.
If your opponent threatens you, identify the threat and the proposition and argue that the threat is unrelated to the truth or falsity of the proposition. Be prudent, anyway: some threats are realistic.