This post discusses a common error in reasoning, the False Choice, also known as the False Dichotomy, the Bifurcation fallacy, the Either-Or fallacy, the Fallacy of Negation, the False Dilemma, and for a common variant with only three options, the False Trichotomy.
This uses informal, or language-grounded, logic, and takes the form of a Dilemma, a class of argumentation that takes its effectiveness from resemblance to a formal argument known as a Disjunction.
A Dilemma, false or not, unlike a Disjunction, has a conclusion that follows only to a degree of probability, not necessarily or with complete certainty.
As a fallacy, this argument uses a misleadingly simple choice of two or otherwise too few options, one assumed as true to the negation, discredit, or rejection of all alternatives. In all variants, this falsely constrained selection of options are presented as though they were the only ones.
In any realistic choice there is often a much greater selection of options to take than rhetorically suit the purposes of those who like to use this argument strategy.
On occasion, however there are exceptions, when there do exist a restricted selection of options, as when a prediction made by a scientific hypothesis is either provisionally validated or falsified, or with the argument against theistic moral theories from the dialogues of Plato, Euthyphro’s Dilemma. Sets of choices that reflect realistic limits would not count as a commission of this fallacy.
I’ll provide a few of examples of the False Choice below:
Either young-Earth creationism is true or we came about through blind evolution. But I declare evolution to be false as it contradicts the literal truth of scripture, which I know to be true. Since evolution is false, young-Earth creationism must be true.
You either worship my God, or you worship the Evil One. You don’t worship my God, and since everyone worships something, you must worship the Evil One.
If these are redone as false trichotomies, we get:
Either young-Earth creationism, Intelligent design, or Darwinism is true, and since Darwinism and Intelligent design are false, young-Earth creationism must be true.
This argument completely ignores the vast variety of theological systems and creation myths of all the world’s cultures, past and present, misleadingly presenting an anachronistic 19th century caricature of modern evolutionary science, the creation myths from Genesis (Both of them!) as interpreted by biblical literalists, and Intelligent design as the only possible options.
There is also:
You either worship my concept of God, the Evil One, or the fleshy gods of materialistic science.
This ignores the fact that one may in fact worship nothing at all, no gods, no masters, no devils, no objects of worship of any kind, as is usually the case with atheists.
The rest are simple (and of course, simplistic) dichotomies…
You’re either a believer and a theist, or you’re a skeptic and an atheist.
Two words suffice to refute this: Martin Gardner.
Anyone who doesn’t support the Patriot Act supports terrorists!
Either the girl broke her ex-boyfriend’s jaw with that slugger, or it started flying around and fractured his jaw by itself!
Either your cat stole my burrito or maybe a psychic just teleported in and grabbed it? Suuure…
If you are not with us, you are against us.
You’re either pro-choice or pro-life. There’s no middle ground!
Note that realistically, not all imaginable options in a set of alternatives need to be considered, only those options that are somehow meaningfully testable, as with the rule of thumb known as Occam’s razor, or the principle of theoretical economy.
Also, there is at least one other reason that this argument is not always a fallacy, such as when it is used to further the goal of advancing a critical discussion, and not merely block further consideration or thwart attempts to resolve a controversy.