False dichotomy

A logical fallacy that forces a conclusion by presenting as if there are only two options when in reality there are more. Also called false dilemma.

It takes the form “If it’s not A, it’s B,” and if A and B are not mutually exclusive or exhaustive, this inference does not hold. For example, “If you’re not perfect, you’re not vegan” erases the degree of practice that lies in between (Reference: Veganism).

Distinguishing from Binary Distinction

Not all dichotomies are false dichotomies. There are distinctions that are mutually exclusive and exhaustive, such as even and odd numbers, and there are distinctions that are useful as terms to refer to concepts even if the boundaries are ambiguous (Reference: Differences between framework and library).

Problem cases can be broadly divided into two.

• False Dilemma: When an argument unfairly narrows the options to two. Error described above.
• Distortion of Binary Categorization: Cutting a continuous or multidimensional reality into two categories and believing that those categories accurately reflect reality. This includes gender dichotomy and animal-human dichotomy (Reference: Dichotomy).

There is also an error in the opposite direction. Claiming that the distinction itself is meaningless because the boundary is ambiguous is called continuum fallacy. The fact that “there is a wide gray area between narrow areas of white and black” does not imply that “there is no white or black” (Reference: What makes eugenics bad).