Development of initial-consonant production in relation to the acquisition of words is investigated. Longitudinal data of three children are analysed from about age 1; 0 until the total recorded lexicon reaches 50 or more words. Using the word as the basis of analysis, PHONE CLASSES are set up for each child and are followed through time in PHONE TREES. As in historical sound change, both lexical and phonetic parameters are involved. Phonological idioms, saliency rules, universal order hypotheses, and acquisition strategies are discussed. Tentative suggestions are made toward a model of phonology.