In linguistics, double articulation, duality of patterning, or duality is the fundamental language phenomenon consisting of the use of combinations of a small number of meaningless elements (sounds, that is, phonemes) to produce a large number of meaningful elements (words, actually morphemes). Its name refers to this two-level structure inherent to sign systems, many of which are composed of these two kinds of elements: 1) distinctive but meaningless and 2) significant or meaningful.
It is one of Hockett's design features.