Symmetry in Syntax: Merge and Demerge

Abstract

This article proposes a theory of phrase structure which is free from unmotivated stipulations as much as possible and which is also compatible with the most restrictive theory of parametric variation currently available (cf. Fukui (1995)), with a special focus on the nature and role of linear order and functional categories. A hypothesis called the "Symmetry of Derivation" is put forth, according to which the computations in the overt syntax (i.e., the pre-Spell-Out computations) and the computations in the (pre-Morphology) phonological component are "symmetric" in the sense that they form mirror images of each other. More specifically, we propose that language computation maps an array of linguistic elements to an interface representation in such a way that it starts with a lexical item (a head) proceeding in a bottom-up fashion (Merge) and at some point of this step-by-step derivational process (Spell-Out) starts "decomposing" the structures already formed in a top-down fashion ("Demerge") until the derivation reaches a completely unstructured sequence with a fixed linear order. It is shown that this symmetry principle explains the major properties of phrase structure in an elegant way. The principle accounts for the apparently universal "leftness" property of Spec in a straightforward way by attributing its leftness to the fact that a Spec, by definition, is the first maximal projection in a given phrase that the top-down computation Demerge encounters. With respect to the order between a head and its complement, which allows for cross-linguistic variation (head-initial vs. head-last), the symmetry principle predicts that the head-last order reflects the "base" order involving no relevant movement whereas the head-initial order is derived by movement, in clear contrast with Kayne's (1994) approach. The difference between head-initial English and head-last Japanese is, then, attributed to different properties of a "light verb" v (Chomsky (1995b)): v has the property of attracting V in English but not in Japanese. Numerous theoretical and empirical consequences are shown to follow in an interesting way from this hypothesis, coupled with the symmetry principle of derivations.