argumentum ad fidentia

Also known as: against self-confidence

Description: Attacking the person’s self-confidence in place of the argument or the evidence.

Logical Form:

Person 1 claims that Y is true, but is person 1 really sure about that?

Therefore, Y is false.

Example A

John: I had a dream last night that I won the lottery!  I have $10000 saved up, so I am buying 10,000 tickets!

Sarah: You know, dreams are not accurate ways to predict the future; they are simply the result of random neurons firing.

John: The last time I checked, you’re not a neurologist, so how sure are you that I am not seeing the future?

Sarah: I guess it’s possible you can be seeing the future.

Explanation: Although Sarah is trying to reason with his friend, John attempts to weaken Sarah’s argument by making Sarah more unsure of her position.  This is a fallacious tactic by John, and if Sarah falls for it, it is fallacious reasoning on her part.

Example B

Todd: You claim that you don’t believe in the spirit world that is all around us, with spirits coming in and out of us all the time.  How can you be sure this is not the case?  Are you 100% certain?

Warren: Of course not, how can I be?

Todd: Exactly! One point for me!

Warren: What?

Explanation: This is a common fallacy among those who argue for the supernatural or anything else not falsifiable.  If Warren was not that reasonable, then he might start to question the validity of his position, not based on any new counter evidence presented, but a direct attack on his self-confidence.  Fortunately for Todd, he holds no dogmatic beliefs and is perfectly aware of the difference between possibilities and probabilities.

Exception: When one claims certainty for something where certainty is unknowable, it is your duty to point it out.

Tip: Have confidence that you are probably or even very probably right, but avoid dogmatic certainty at all costs in areas where certainty is unknowable.