This research focuses on the possibility to compare prelinguistic utterances and linguistic utterances of the first words period. The definition of protoword and word notions is not clear; while we consider different approaches to determine them: historical, epistemological and experimental. The contribution of the historical approach is essential to identify the problem and to bethink how a society in different historical periods considers speech. This section allows us to highlight two elements: the question of the speech emergence implies the notion of social representation, and nowadays, the word emergence is during the first words period. The analysis of this period leads to our epistemological part which defines units of this period: protowords and words. Once units identified, we perform a longitudinal analysis of four children, from one to two years. Firstly, we identify a phenomenon of substitution of protowords in words. Secondly, we observe two common elements in these productions: prosody and phonology. We show that prosody provides a common framework to ensure the transition between protowords and words, and that phonology is the area where differences are observed: the words are the place for the development of complex phonological structures, unlike protowords. We consider that the emergence of speech is when the children prefer using words as verbal communication medium, instead of protowords, and that this feature is the object of phonological development.
