False Dichotomy

A false dichotomy is an informal logical fallacy in which it is falsely claimed that one and only of of two (or a small number) of possible states of affairs could pertain. Often arguments committing this fallacy assert “either X or Y”, where Y is some obviously undesirable or absurd possibility. Since Y must obviously be rejected, it is therefore concluded that X must be accepted or be true. Establishing that an argument is committing a false dilemma generally requires establishing that the set of possibilities offered is not comprehensive. As such, providing a third or fourth plausible choice not outlined in the original argument is typically sufficient to establish that this fallacy has been committed, and that therefore the argument needs to be reformulated. Some classic catchphrases which are obvious false dilemmas include:

“If you’re not part of the solution, you’re part of the problem.”

“If you’re not with us you’re against us.”

A more sophisticated example of this fallacy would be an argument such as the following:

“Either there is some immaterial soul which allows us to make decisions non-deterministically, or human beings are just robots acting in accordance with the programming of our genes and environment.”

This argument is an instance of a false dilemma because it ignores the possibility that both determinism and free will could coexist, a philosophical position known as compatibilism. Since the argument presents a dichotomy between two possibilities which are not established as being mutually exclusive, it exemplifies a false dilemma. Of course, it may be the case that determinism and free will are incompatible, and thus the dichotomy is an accurate one, however that has not been established in the argument given here.

Further Reading

False dilemma: overview from Nizkor Project

False dilemma: overview from Logically Fallacious

Black-or-White fallacy: overview from Fallacy Files

False dichotomy: overview from philosophy-index.com