Smith (1973) presents a detailed analysis of his son's phonological development between the ages of two and four.1 The book is impressive, not only for the care with which the analysis was done but also, and more importantly, for the clarity with which central acquisition issues were stated. The analysis of the child's productions was done in two ways: first as a mapping from the adult system and second as a self-contained system. In his introduction, Smith raises seven issues that any theory of language acquisition must address; one of these concerns the nature of phonological change. Smith states that when changes occur in the child's output, they do so in an ‘across-the-board’ fashion. On the basis of this (and other) evidence, Smith concludes that the child must have the adult surface form as his underlying lexical representation. The implication is clear: the child must thus perceive in an adult-like fashion and the deviance of his/her output is due to the articulatory difficulty of certain sounds and sound sequences (and in some cases to certain formal properties of his mapping system).