Cognitive grammar is a cognitive approach to language developed by Ronald Langacker, which considers the basic units of language to be symbols or conventional pairings of a semantic structure with a phonological label. Grammar consists of constraints on how these units can be combined to generate larger phrases which are also a pairing of semantics and phonology. The semantic aspects are modeled as image schemas rather than propositions, and because of the tight binding with the label, each can invoke the other.