The syllable boundary in generative phonology

In Natural Generative Phonology (NGP), the only phonological rules are those which describe alternations that take place in environments that can be specified in purely phonetic terms. As indicated by Hooper, these “‘phonetic terms’ refer to phonological features (that have intrinsic phonetic content) and phonological boundaries (that have a necessary and consistent phonetic manifestation)” (1976:14). Any rule which changes phonological features in an environment described in morphosyntactic or lexical terms is not phonological but morphophonemic. Since by definition a phonological rule cannot contain non-phonetic information, this entails, among other things, the exclusion of any boundary that is not determined by phonetic means. In other words, the syllable ($) and the pause (| |) are the only boundaries which can appear in a phonological rule in NGP. The word boundary (# and ##) and the morpheme boundary (+), which are determined by syntactic and semantic means, can only appear in a morphophonemic rule.