Why is the either-or fallacy an informal logical fallacy?
The either-or fallacy is an informal logical fallacy because it is a content-level error that occurs in inductive arguments. Inductive arguments reason from specific observations to propose general principles. If an inductive argument commits an informal fallacy, it is called “unsound.”
By contrast, formal fallacies are structural errors that occur in formal (or deductive) arguments and make the argument “invalid.”