expressiveness follows from generativity or productivity (a finite number of components combining via rules to produce a potentially infinite arrangement of novel utterances), not of duality per se (one could have a system with 2 levels of the kind referred to as duality, and yet have only finite productivity). For further discussion, see figurae, as well as Hockett's design features, which treats productivity and duality as distinct essential properties of language. Sign languages may have less double articulation because more gestures are possible than sound and able to convey more meaning without double articulation. See also Origin of language Origin of speech References External links Wendy Sandler et alii, "The gradual emergence of phonological form in a new language", 2009. Linguistics Philosophy of language Semiotics Theories of language