dichotomy
1. [ noun ] being twofold; a classification into two opposed parts or subclasses
Synonyms: duality
Examples:

: "the dichotomy between eastern and western culture"

Related terms: classification dichotomize
2. [ noun ] a sorting of a class of things into two mutually exclusive subclasses
Related terms: classification
Similar spelling:   dichotomous
  dichotomize
  dichotomise