dichotomous

Dichotomous describes something divided into two parts that are mutually exclusive and collectively exhaustive. The term derives from the Greek dichotomos, from di- 'two' and chōtos 'cut.' In common usage it applies to any binary division or classification.

In logic and philosophy, a dichotomy is a division of a concept or set into two complementary parts that cover all possibilities, such as true/false or existence/nonexistence. The two parts are mutually exclusive.

In statistics and research, a dichotomous variable (also binary variable) takes on two possible values, often coded as 0 and 1 (e.g., yes/no, male/female in limited contexts). Data with two categories are contrasted with multilevel or continuous data.

In biology and taxonomy, a dichotomous key is an identification tool that leads the user through a sequence of binary choices. Each step offers two contrasting statements; the chosen option directs to the next pair until the organism is identified.

Outside formal usage, dichotomous thinking refers to seeing situations in black-and-white terms, ignoring intermediate possibilities. In statistics and philosophy, dichotomies are useful simplifications but may obscure nuance. The concept is foundational in various disciplines that classify on two poles.