duality of patterning
Definition - A quality of human language such that meaningful signs (e.g. words) are usually made of meaningless parts (e.g. sounds and letters). A finite number of these meaningless parts can be combined to make a potentially infinite number of meaningful utterances.

It is one of the 16 design features of language that distinguish human language from animal communication systems.

Example Usages -

1. “Thus many of what Hockett (1963) called ‘design features’ of language are excluded – e.g. discreteness, arbitrariness, productivity, and the duality of patterning achieved by combining meaningless elements at one level (phonology) to construct meaningful elements (morphemes or words) at another.”
(Source: The Myth of Language Universals: Language diversity and its importance for cognitive science (Nicholas Evans & Stephen Levinson) )

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