This paper examines possessive pronoun forms in Welsh, a feature thought to be undergoing change (Davies, 2016). First, we seek to add to the understanding about how and in which stylistic contexts these forms are used. Second, we examine whether students in Welsh-medium schools with different home language backgrounds show the same sociolinguistic competence. In contrast to what is prescribed in many grammar books, the colloquial form mam fi ‘my mum’ is used at much higher rates than the traditional literary fy mam and sandwich variants fy mam i. This is particularly the case in more casual styles. We also find differences between north and south Wales in overall rates of use, but within the two schools studied, the English home language students broadly show the same patterns and constraints as the Welsh home language students, underlining that language background does not affect the acquisition of sociolinguistic competence.
