dichotomously

Dichotomously is an adverb that describes something done in a manner characterized by a dichotomy: division or contrast into two mutually exclusive parts. It is derived from the adjective dichotomous, which itself comes from Greek dichotomos, from di- “two” and temnein “to cut.”

In logic and philosophy, arguments may be described as presented dichotomously when they reduce a spectrum to two opposing possibilities. In biology and taxonomy, a dichotomous key guides identification by a sequence of choices between two alternatives at each step. In data analysis and research, a dichotomous variable represents a binary outcome, such as yes/no or present/absent. In psychology and behavioral sciences, respondents may be classified dichotomously for certain measures, or tasks may require dichotomous decisions.

Examples include coding survey responses as dichotomously yes or no, or using a dichotomous key to determine a species by successive two-option questions. The term can also imply oversimplification when more nuanced continua are forced into two categories.

See also: dichotomy, binary, binary opposition, dichotomous key.