2 The functional interpretation of child language
The criterion adopted for regarding a vocalization by the child as an instance of language was that there must be an observable and constant relation between the content and the expression : that each particular expression must be observed in at least three unambiguous instances, and its content must be interpreted in functional terms. In practice, however, the distinction between random vocalizations and systematic (that is, linguistic) utterances proved to be obvious, and the latter were found to occur with far more than minimal frequency.