A dichotomy's any splitting of a whole into exactly two non-overlapping parts. In other words, it's a partition of a whole (or a set) into two parts (subsets) that're: mutually exclusive : nothing can belong simultaneously to both parts, and jointly exhaustive : everything must belong to one part or the other. 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. Etymology The term co… (More on Dichotomy)