New speakers of Catalan have come to represent, from a demolinguistic perspective, a substantial part of the community of speakers. Of those who presently speak Catalan as an “habitual language”, 41.6 percent are native speakers of Spanish. In this article, we shall follow up the various ways in which native Castilian speakers incorporate Catalan into their lives. This happens, as we will show, in specific biographical junctures that we call mudes, a Catalan term referring to (often reversible) variations in social performance. Our analysis is based on a qualitative study that included 24 interviews and 15 focus groups covering a total of 105 people of different sexes and linguistic, educational, social and residential backgrounds. We shall give a general overview of these mudes as we typified them: when subjects entered primary school, secondary school, the university, the job market, when creating a new family and when they had children (if they did). The study of linguistic mudes provides, in our view, a new and productive perspective on how people develop their linguistic repertoire, their attachment to specific languages and the significance of these aspects for social identity. It facilitates a processual, time-sensitive analysis that allows to contextualise and critique ethnonationalist discourses that have often saturated our understanding of language use.