Also, multiple origins were not allowed. From 1766 to 1844, the data collected on ethnic origin was apparently inconsistent. This view is likely largely correct although a margin of error would exist, as some would have been Gaelic speakers, others might have assimilated to the francophone group while many of other ethnic origins might have become English speaking. Thus, the tool of measurement in this period was imperfect, and one that was possibly increasingly incorrect as time passed. From 1931, the Canadian census asked not only about ethnic origins but, as well, about mother tongue.
Mother tongue is defined as the first language learned as a child and still understood.
Since it directly addressed language mastery, it evidently became a better measurement of the linguistic situation than ethnic origin. The two questions permitted an evaluation of assimilation, as people of British origin who listed a mother tongue other than English had evidently been assimilated to another group. They especially enabled the measurement of the great attractiveness of the English language to the people of non British origins. However, again the census only allowed one mother tongue to be listed when, frequently, because of the increasing incidence of cross-cultural marriages, more than one language was learned simultaneously. It also did not take into consideration that, while a language may still be understood, it might rarely, if ever, be used, or that one might identify with another linguistic group despite one's mother tongue.