Recent research has linked the emergence of grammatical morphemes to a phenomenon which appears very early in language development, when children are still essentially single-word speakers: i.e., the production of short, often vocalic, elements at the beginning of words. This paper presents fine-grained analyses of these elements as they occur in the longitudinal study of a child in the process of acquiring French. The pattern of results obtained suggests that during the first three months the production of these elements appears to correspond to a pre-morphological organisation based on the child's apprehension of sonoric and prosodic regularities present in the language. This first system changes into a qualitatively different, proto-morphological, one in which incipient characteristics relating to word classes and grammatical morphology appear at the same time. In Piagetian constructivist theory ,this discontinuity in the contents of acquisitions can very well result from a continuous underlying developmental process.