Fallacy · Slippery words and shapes
Denying the antecedent
Also called: “If A then B; not A, so not B”
Reasoning from “if A then B” and “not A” to “not B”, which does not follow.
What it is
“If you study, you’ll pass” does not mean that only studying leads to passing. Without A, B might still happen another way. The valid move in the other direction is “not B, so not A”.
An example
“If you eat breakfast, you’ll have energy. You skipped breakfast, so you’ll have no energy.” A good night’s sleep or lunch might do the job.
How to spot it
An “if… then…” is treated as if it were “only if… then…”.
How to answer it
“Is A the only way to get B?”
When it is not a fallacy
If the rule really is “only if” (B happens only when A does), the inference is valid. Check which rule was stated.
Printable sheet of all fallacies
Cite or share this page
A plain reference you can paste into notes or an essay:
Quest2Reason. “Denying the antecedent.” https://quest2reason.com/learn/ideas/fallacies/denying-the-antecedent. Accessed 13 November 2026.