The notion of duality of patterning (henceforth DoP), at least for readers of this special issue, is probably most closely associated with Charles F. Hockett's project of identifying the ‘design features’ of language in order to characterise the ways in which human language is unique among biological communication systems (Hockett 1958: chapter 64; Hockett 1960; Hockett and Ascher 1964). Roughly speaking, DoP refers to the fact that the meaningful units of language – words or morphemes – are made up of meaningless units – phonemes or features – whose only function is to distinguish the meaningful units from one another. Stated this way, the idea seems quite straightforward, and to have it explicitly stated as a property of language seems a useful insight. In fact, though, of all the design features discussed by Hockett, DoP seems to have engendered the most confusion. The idea that meaningful units are composed of meaningless ones seems simple enough, but many complications arise when we look more closely. The goal of this short paper is to document some of the complications and perhaps alleviate some of the confusion.