A linguistic theory devised by the American linguist Sydney M. Lamb (b.1929), as expounded initially in Outline of Stratificational Grammar (1962), which models language as a system of several related layers (or strata) of structure. Six strata are recognized for English and many other languages: the component of phonology comprises the hypophonemic (or phonetic) and phonemic strata; grammar comprises morphemic and lexemic strata; and semology comprises the sememic and hypersememic (or semantic) strata. Each stratum is organized in terms of a set of stratal systems, and each system deals with an aspect of linguistic structure which has to be stated independently of the structures operating at other strata. Two types of patterning are recognized: tactic analysis (the patterns of sequential arrangement within each stratum) and realizational analysis (the relationship between units operating at higher and lower levels between strata). A parallel terminology is used for each stratum: there is a ‘hypophonemic / phonemic / morphonemic / lexemic / sememic / hypersememic’ system consisting of various structural patterns (e.g. ‘hypophonotactic / phonotactic’, etc.), defined in terms of ‘hypophonemes / phonemes’, etc., and realized as ‘hypophons / phons / morphons / lexons’, etc.