Post written by François Grosjean.
A bilingual's languages can wax and wane over time. Significant life events such as starting school, getting a job, moving to another region or country, settling down with a partner/spouse, losing a close family member with whom a language was used exclusively, etc. may change the relative importance of the bilingual's languages as well as explain the acquisition of new languages and the forgetting of older ones.
To illustrate this, allow me to quickly skim through my own language history. I started as a monolingual in French and it is only at age eight that I acquired English by being put in an English speaking boarding school. After a year or two, English became my dominant language and remained that way for some ten years. During that time, I also acquired Italian and became quite fluent in it.
At age eighteen, I went to college in France and little by little French won back its "most important language" status. Italian started declining as I no longer used it very much. After ten years in France, my family and I moved to the United States where we lived for twelve years. English became once again my dominant language and French dropped a bit in fluency and use. It is at that time that I learned American Sign Language (ASL) but I was never very fluent in it, much to my regret.
Finally, when I was forty, we moved to the French-speaking part of Switzerland and, once again, my languages reorganized themselves. Currently I use French daily as I do English (especially in its written modality), whereas ASL and Italian are slowly being forgotten (see here).
Stepping back from this quick overview of my own language history (other bilinguals have their own fascinating histories, sometimes far more complex than mine!), a few points come to mind. First, it counters a myth that has already been discussed that real bilinguals acquire their two or more languages in their very early childhood (see here). In fact, one can become bilingual at any time during one's lifetime. Even adults can become just as bilingual as those who acquired their languages in their early years, even though they may retain an accent in their new language(s).
A second point is that new situations, new interlocutors and new language functions will create new linguistic needs, and these will change a bilingual's language configuration. There will be periods of stability and periods of linguistic restructuring. During the latter, a language may be strengthened, another may lose its importance and even start to be forgotten, yet another may be acquired, and so on.
A final point is that global dominance in a language can change over time. In my case, it changed four times due to my moving back and forth between countries. In addition, there were two periods of some ten years each where my first language was not my dominant language. Admittedly, it is not rare to find bilinguals who go from being dominant in their first language to being dominant in their second language, after a period of transition, of course. It is a bit rarer, though, to revert back to being dominant in your first language and then, some years later, to change once again, as in my case.
When speaking of language dominance, one should be careful to differentiate between overall dominance and dominance by domains of language use. Overall dominance may change, as shown above, but some domains of use (e.g. speaking to immediate or distant family members, using language for well-learned behaviors or for religious activities, etc.) may remain tied to one, and only one, language (see here).
So next time someone asks you what your dominant language is, and how it has evolved over time, ask back, "Do you mean overall dominance or by domain of use?" If their eyes glaze over at that point, switch subjects... or invite them to read my blog!
François Grosjean. Languages across the lifespan. Chapter 8 of Grosjean, F. (2010). Bilingual: Life and Reality. Cambridge, Mass: Harvard University Press.
"Life as a bilingual" posts by content area.
François Grosjean's website.