Penthouse principle

The penthouse principle, a term in syntax coined by John R. Ross in 1973, describes the fact that many syntactic phenomena treat matrix (or main) clauses differently from embedded (or subordinate) clauses:

The penthouse named in the principle is the top-floor of a highrise apartment building, and is a metaphor for the matrix clause in a multi-clause structure (which, when diagrammed in usual phrase marker notation, contains the highest clause node in the structure). Perhaps the best-known example of a penthouse principle effect is the distribution of subject-auxiliary inversion in constituent questions in English, which in many (but not all) varieties of English is restricted to matrix clauses:

Compare:

Other phenomena falling under the penthouse principle are V2-effects in the Germanic languages and the distribution of declarative markers, imperative morphology, and of various particles in a variety of languages.

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