Dichotomy

A dichotomy is any splitting of a whole into exactly two non-overlapping parts, meaning it is a procedure in which a whole is divided into two parts. It is a partition of a whole (or a set) into two parts (subsets) that are: Such a partition is also frequently called a bipartition.
 * jointly exhaustive: everything must belong to one part or the other, and
 * mutually exclusive: nothing can belong simultaneously to both parts.

The two parts thus formed are complements. In logic, the partitions are opposites if there exists a proposition such that it holds over one and not the other.

The term comes from the Greek dichotomia (Greek: "διχοτομία") (divided): dich- (form of dícha, in two, asunder); tomia- a combining form meaning cutting, incision, excision of an object