Constraining linguistic metatheory by demanding that it allow the construction of grammars for all the frequently occurring idiolects of standard American English is shown to narrow the choices among competing theoretical positions. In this way data from a nonhomogeneous speech community are used to illuminate rather than cloud a theoretical question. "While"-clauses are taken as exemplary of the class of English adverbial clauses in general and temporal clauses in particular. In surface structure, "while"-clauses are shown to be Chomsky adjoined to the verb phrase if postposed and to be attached directly to the S-node if preposed or medial. Following M. Geis (1970) the internal structure is shown to be that of an adverbial relative clause. A rule of Oblique Equi-NP Deletion is motivated to account for subjectless "while"-clauses. Two alternative deep structure sources for "while"-clauses are discussed: The higher-S and lower-S analyses. Data from 345 native speakers of English are shown to require the construction of three distinct grammatical descriptions of the constraints on Oblique Equi-NP Deletion. Requiring that linguistic theory allow just these grammars to be written eliminates the possibility of constructing grammars in which no rules are extrinsically ordered. The higher-S analysis is shown to require a serious violation of the Strict Cycle Condition, while the lower-S analysis is shown to require the use of an ad hoc category and to predict the existence of a dialect of dubious existence. (Author/KM)