In informal logic, the fallacy of the accident mistakenly applies a general rule to a particular case that is atypical ; the rule does not apply to this case. An example:

• General rule: humans have two legs.

• Atypical case: Harry the one-legged pirate is a human.

• Fallacious conclusion: Therefore, Harry has two legs.

If the general rule were a universal premise, then it would have to apply to all humans. Instead, this is a general rule that is not universal, so it is fallacious to apply it to an exceptional case.

The fallacy of the converse accident instead tries to derive a general rule from a specific case. It is not possible to do this, as the single case may very well be exceptional. An example:

• Atypical case: The human Harry has one leg.

• Fallacious conclusion: Therefore, all humans have one leg.