Phonological Optimization and Syntactic Variation: The Case of Optional That

0. Introduction The principle of Phonology-Free Syntax (see papers in Zwicky, 1969) states that syntax should not be influenced by phonological constraints. This predicts that choice in syntactic variation should not be affected by phonological constraints, such as the avoidance of identical adjacent elements (Frisch et al., 2004; Leben, 1973). Only a few studies have investigated the extent to which phonological encoding can influence syntactic encoding and they have come to conflicting results (see Bock and Eberhard, 1993; Haskell and MacDonald, 2003; MacDonald et al., 1993). I investigate the influence of phonological optimization at different levels of linguistic form on so called optional that, as in the following complement clauses (CC*s) and relative clauses (RC*s):