I wonder what it means when the 1891 (and later) census gives "Welsh" under "languages spoken". I assume if it says 'English', it really means 'only English', and if it says 'both' it means the person could communicate satisfactorily in either English or Welsh. But when it only says 'Welsh', does it mean the person could speak only Welsh, or does it mean no more than that Welsh was the person's preferred language? Was there a formal meaning or use imposed on the registrars?