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A false dilemma (also called black-and/or-white thinking, bifurcation, denying a conjunct, the either-or fallacy, false dichotomy, fallacy of exhaustive hypotheses, the fallacy of false choice, the fallacy of the false alternative, or the fallacy of the excluded middle) is a type of informal fallacy that involves a situation in which limited alternatives are considered, when in fact there is at least one additional option. The opposite of this fallacy is argument to moderation.
The options may be a position that is between two extremes (such as when there are shades of grey) or may be completely different alternatives. Phrasing that implies two options (dilemma, dichotomy, black-and-white) may be replaced with other number-based nouns, such as a "false trilemma" if something is reduced to only three options, instead of two.
False dilemma can arise intentionally, when fallacy is used in an attempt to force a choice (such as, in some contexts, the assertion that "if you are not with us, you are against us"). But the fallacy can also arise simply by accidental omission of additional options rather than by deliberate deception.
Some philosophers and scholars believe that "unless a distinction can be made rigorous and precise it isn't really a distinction." An exception is analytic philosopher John Searle, who called it an incorrect assumption which produces false dichotomies. Searle insists that "it is a condition of the adequacy of a precise theory of an indeterminate phenomenon that it should precisely characterize that phenomenon as indeterminate; and a distinction is no less a distinction for allowing for a family of related, marginal, diverging cases." Similarly, when two options are presented, they are often, though not always, two extreme points on some spectrum of possibilities; this can lend credence to the larger argument by giving the impression that the options are mutually exclusive, even though they need not be. Furthermore, the options in false dichotomies are typically presented as being collectively exhaustive, in which case the fallacy can be overcome, or at least weakened, by considering other possibilities, or perhaps by considering a whole spectrum of possibilities, as in fuzzy logic.
Morton's Fork, a choice between two equally unpleasant options, is often a false dilemma. The phrase originates from an argument for taxing English nobles:
This is a false dilemma and a catch-22, because it fails to allow for the possibility that some members of the nobility may in fact lack liquid assets, as well as the possibility that those who appear poor actually are poor.
The presentation of a false choice often reflects a deliberate attempt to eliminate the middle ground on an issue. A common argument against noise pollution laws involves a false choice. It might be argued that in New York City noise should not be regulated, because if it were, the city would drastically change in a negative way. This argument assumes that, for example, a bar must be shut down for it to not cause disturbing levels of noise after midnight. This ignores the fact that the bar could simply lower its noise levels, and/or install soundproofing structural elements to keep the noise from excessively transmitting onto others' properties.
In psychology, a phenomenon related to the false dilemma is black-and-white thinking. Many people routinely engage in black-and-white thinking, an example of which is someone who labels other people as all good or all bad.
The Latin phrase falsum in uno, falsum in omnibus which, roughly translated, means "false in one thing, false in everything", is fallacious in so far as someone found to be wrong about one thing, is presumed to be wrong about some other thing entirely. Arising in Roman courts, this principle meant that if a witness was proved false in some parts of his testimony, any further statements were also regarded as false unless they were independently corroborated. Falsum is thus a fallacy of logic. The description that an initial false statement is a prelude to the making of more false statements is false; however, even one false premise will suffice to disprove an argument. This is a special case of the associatory fallacy.
Falsum in uno, falsum in omnibus status as a fallacy is independent of whether it is wise or unwise to use as a legal rule, with witnesses testifying in courts being held for perjury if part of their statements are false.