In the field of dialectology, a diasystem or polylectal grammar is a linguistic analysis set up to encode or represent a range of related varieties in a way that displays their structural differences. The term diasystem was coined by linguist and dialectologist Uriel Weinreich in a 1954 paper as part of an initiative in exploring how to extend advances in structuralist linguistic theory to dialectology to explain linguistic variation across dialects. Weinreich's paper inspired research in the late 1950s to test the proposal. However, the investigations soon showed it to be generally untenable, at least under structuralist theory. With the advent of generative theory in the 1960s, researchers tried applying a generative approach in developing diasystemic explanations; this also fell short. According to some leading sociolinguists, the diasystem idea for incorporating variation into linguistic theory has been superseded by William Labov's notion of the linguistic variable. As such, the concept has not been part of any substantial linguistic theory and the term has limited currency in linguistics. Origin of the concept first suggested comparing accents by their synchronic states, rather than by comparing their different historical developments. He classified sound differences between dialects into three types: Phonological: the inventory phonemes and contextual restrictions, which may vary between dialects. For example, speakers of Castilian Spanish have the phonemes and , whereas Western Hemisphere dialects of Spanish have just the latter. Phonetic: how phonemes are realized phonetically. For example, most dialects of English have strongly aspirated in words like park, tool, and cat, but some Northern English accents do not feature such aspiration. Etymological distribution: the distribution of phonemes among member words in an interdialectal lexical correspondence set. For example, most English varieties contrast and , but some use the former in words like bath and grass and others use the latter. Despite Trubetzkoy's proposal, linguists continued to consider variation between varieties outside of the scope of inquiry of grammar construction; each variety, in their thinking, should only be studied on its own terms. Inspired by Trubetzkoy, proposed a synthesis of linguistic geography and descriptive linguistics by applying the structuralist concept of grammar to the description of regular correspondences between different varieties; a resulting supergrammar, which he called a diasystem, would be consistent with the individual grammars of all the member dialects. A diasystem is a higher order system and its component units of analysis would accordingly be abstractions of a higher