This paper attempts to articulate contributions from the language sciences, psychology and educational sciences to address, in a strongly interactionist perspective, the question of the role of language in human functioning. This reflection lead us to return to central notions such as sign, meaning, interaction, development, activity, from a theoretical and methodological point of view. The methodological point of view give us the opportunity to problematize the unit (or units) of analysis capable of allowing a non-reductionist seizure of language dynamics within human functioning. We base our reflection on the contribution of several authors, including Saussure, Bloomfield, Coseriu, Vygotski, Piaget, but also contemporary works in connection with our own research.