Mending your Ps & Qs

0. Introduction Phonological representations include sequences of featural specifications, pq. Two properties can be observed about such sequences: (i) for a sequence pq to be of significance for the phonology of a language, p must be perceptibly different than q; (ii) to produce a sequence pq, the articulators must start in the configuration for p and then change into the configuration for q. Given constraints on both perception and production, p and q may interact. The likelihood and nature of such interaction will be determined by shows that interaction may be affected by proximity, with p and q most likely to interact if string-adjacent, more likely to interact if the pq sequence is interrupted by a consonant than by a vowel, and more likely to interact in adjacent syllables than if arbitrarily distant within a word. Interaction may be affected by similarity. Two segments are more likely to interact if they are identical, if they share major class features, or if they share features of phonation or place. Phonetic similarity also increases the likelihood of interaction, whether the similarity is based on acoustics or articulation. Domains may also affect interaction, with effects more likely to occur within a small cohesive domain (such as the morphological root or stem) than in larger less cohesive domains (such as the word or the phrase). The study of such sequential interactions is central to understanding segmental phonology. When a sequence meets certain criteria, segments may assimilate to each other, dissimilate from each other, metathesize, and so on. These patterns are of significant interest because the interaction of simple, phonetically transparent relations can give rise to surface patterns that are complex and even opaque. If we assume that natural language phonologies involve complex interactions between simple constraints, as in Optimality Theory (Prince & Smolensky 1993), then the observation that simple constraints are frequently phonetically transparent raises the possibility that such constraints are learned, not stipulated as part of Universal Grammar. That is, a learner