 The idea was that a sentence has both a deep structure (DS), which reflects semantically relevant relations between verbs and their arguments, and a surface structure (SS) that may include displaced (or pleonastic) elements. In some cases, pronunciation might depend on further transformations of SS, resulting in a distinct “phonological form” (PF). Linguists posited various constraints on these levels of grammatical structure, and the transformations that relate them. But as the theory was elaborated and refined under empirical pressure, various facts that apparently called for explanation in these terms still went unexplained. This suggested another level of grammatical structure, obtained by a different kind of transformation on SS. The hypothesized level was called ‘LF’, intimating ‘Logical Form’; and the hypothesized transformation—called ‘Quantifier Raising’ because it targeted the kinds of expressions that indicate (restricted) quantifiers—mapped structures like (28S) onto structures like (28L).