Conditional fallacy

"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." RatW.18
See: Fallacy; Fallacies.