When is a word a word?

Although adult-based words co-occur in the period of transition to speech with a variety of non-word vocalizations, little attention has been given to the formidable problem of identifying these earliest words. This paper specifies explicit, maximally 'inclusive' identification procedures, with criteria based on both phonetic and contextual parameters. A formal system for evaluating phonetic match is suggested, as well as a set of child-derived functional categories reflecting use in context. Analysis of word use across two samples of 10 children each, followed from 0;9 to 1;4, provides evidence to suggest that context-bound words can be 'trained' by focusing on eliciting language, but that the timing of context-flexible word use remains independent of such training.