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A conditional fallacy may or may not be a logical fallacy, conditional on whether or not one of their premises is accepted.
Conditional fallacies are almost always informal fallacies. However, if comparing multiple systems of logic (which would imply different valid and invalid logical structures, and thus different formal fallacies) then it may be possible for a formal fallacy to be conditional.
An informal conditional fallacy follows the form:
P1: X is Y.
P2: Being Y causes something to be true / to be false / etc.
C1: X is true / false / etc.
This is not always fallacious. For example, a good (rational) conditional argument:
- P1: Global warming is agreed to exist by over 95% of climatologists, making it the scientific consensus.
- P2: The scientific consensus is probably true.
- C1: Global warming probably exists.
The problem only occurs when Y is something stupid. For example, a bad (fallacious) argument from authority:
- P1: Creationism is agreed to be true by atleast 250 people.
- P2: Because some of those 250 people are scientists, Creationism is probably true.
- C1: Creationism is probably true.
 See also
- Category:Conditional fallacies
- Logical fallacy
- Formal fallacy
- Informal fallacy
- Fallacious argument style