This article questions the status of the mother tongue conceived in its determining role in children's speech. It is important to note that the concept of mother tongue is marked by heterogeneity; it implies a great variety that, in some way, is related to the theoretical line to which the researcher of language acquisition is affiliated. We approach this concept, initially, from the cognitive-social perspective of a linguistic model, with the sole intention of bringing to light the mark of difference of the mother tongue assumed in this work, which is inseparably linked to the Lacanian notion of lalangue. This mark consists of the equivocity that constitutes lalangue, causing ruptures in the patterns of the language. Thus, such a proposal has, as its source ground, Lacanian psychoanalysis, which is affected by Saussurean linguistics, which underlies our attempt to bring to light the effects provoked, on the researcher's listening to children's speech, by the crossing between notions of linguistics and of psychoanalysis. In order to provide some empirical visibility to the misunderstanding implied in lalangue, we refer, by way of illustration, to excerpts from a child's speech, at an early stage of their linguistic trajectory.
Keywords: Language acquisition. Mother tongue. Lalangue.