For both structural and cognitive reasons, natural languages are characterized by their plasticity, by the ease with which the representations borne by the units composing them are subject to change. Polysemy and polyreference are the general rule among languages. In English for example the word greens can refer to village commons, leafy vegetables or members of a political party. Inversely, different units can refer to the same thing, such as roe and caviar, or hepatitis and jaundice. There is no one-to-one relation between form and meaning, either within a language or across languages. For instance, in French, les verts ‘the greens’ refer to the members of a political party, to set game pawns or to a national football team. From this view point, variation within languages (polysemy, synonymy), echoes variation from language to language and raises the question of how it is possible to say “the same thing” differently and what is at stake in this variation. Whereas this plasticity in meaning ensures both the referential power of a language and a form of optimization for the system, it also entails another of language’s defining characteristics - ambiguity and its communicative corollary: misunderstandings. That communication remains nonetheless possible is because the factors of variation in language are submitted to processes of regulation and meaning stabilization. In this presentation, I will begin by attempting to highlight a certain number of variation factors at the level of the isolated (lexical) units. Semantic variation is considered as inherent to language structure and driven by common universal cognitive mechanisms which are accounted for by a dynamic conception of meaning construal. Units appear to be the seat of most variations, within and across languages, because meaning is construed in extremely varied ways according to common mechanisms which will be explored. Then I will try to show that in language activity, virtual units undergo certain operations whereby they are incorporated into utterances, and to highlight this different operations of the sentence level, which permit a certain stabilization in meaning but also occasion communicative failures. The discourse level is the seat of meaning construal mechanisms which contribute both to the general polysemy of lexical units and to the stabilization of their meaning within a particular utterance. My approach is entrenched in cognitive linguistics and proposes some new concepts or tools, such as « the depth dimension of language », « meaning attractors » and « semantic shift », that I found useful for describing both the variation at the level of linguistic units, the stabilization and progressive construal of meaning in utterance, and also the possibility to activate several meanings of the same word in a single utterance. This sort of semantic layering is the source of misunderstanding but also the mainspring of rhetoric, puns, or advertising. Depending whether, in communication, the speaker is the driver or the passenger of this referential power of language and its plasticity in meaning.