Post written by François Grosjean.

In one of the very first posts in this blog, I explained how bilinguals usually acquire and use their languages for different purposes, in different domains of life, with different people. Different aspects of life often require different languages. I have called this the Complementarity Principle (see here).  

François Grosjean
Source: François Grosjean

The figure on the left helps us visualize the principle. Each quadrilateral represents a domain of life such as work / studies, home, family, shopping, leisure, administrative matters, holidays, clothes, sports, transportation, health, politics, etc. The person who is depicted here, a trilingual in languages a, b and c, uses language a (La) in seven domains of life, Lb in three domains, both La and Lb in five domains, and all three languages (La, Lb and Lc) in just one domain. Some domains, therefore, are specific to one language (ten in all), and others are shared by two or three languages (six in all). Any bilingual can be characterized in this way and will have a pattern that is specific to him or her.

The Complementarity Principle plays a large role in various aspects of bilingualism, one of them being language dominance. Li Wei of University College, London, defines the dominant bilingual as someone with greater proficiency in one of his or her languages and who uses it significantly more than the other language(s). In addition to language proficiency and language use, other factors are sometimes mentioned by researchers when accounting for dominance such as when the language was acquired, the bilingual's ability to read and write that  language, the speed and efficiency with which it is processed, and so on.

Researchers have long tried to measure dominance. Outside judges can evaluate the bilinguals' languages such as their pronunciation and the extent of their vocabulary, or the bilinguals can be given various tests such as naming pictures, recognizing words, carrying out a command, or translating sentences from one language to the other. From the various measures obtained, specialists give the participants a dominance rating: the person is dominant in language A, or dominant in language B, or balanced in both languages (if such a person exists).

However, these various approaches have been criticized for reducing the complexity of the bilingual's language knowledge and behavior to a number of simple tasks often given in just one language. In addition, the cut-off point in the results of a particular task that is used to separate dominant from balanced bilinguals is arbitrary. It is also the case that many people use more than two languages in their everyday life which complexifies things even more.

Bilinguals can also be given language background questionnaires to fill out with questions that pertain to when and how the languages were learned, when the respondents started feeling comfortable speaking each language, how and when the languages are used, how proficient the bilinguals feel in each of their languages, etc. A dominance index is then calculated based on the answers given.

All these measures, both objective and subjective, may produce a global measure of dominance and may confirm, for example, that bilinguals are globally dominant in one of their languages, but they do not take into account that some domains of life are specific to a language. In the figure above, the bilingual depicted is globally dominant in La (13 domains counting shared domains), but there are three domains in which she uses Lb exclusively. With adequate assessment tools, it would probably be fairly easy to show that this bilingual is dominant in Lb in these domains. Thus, one can be globally dominant in a specific language but be dominant in the other language for particular domains of life.

Even though the Complementarity Principle puts the emphasis on language use, it has an indirect effect on proficiency, the other variable in Li Wei's description of dominance in the bilingual. If a language is spoken in a reduced number of domains and with a limited number of people, then it will not be developed as much as a language used in more domains and with more people. It is precisely because the need and use of the languages are usually quite different that bilinguals do not develop equal and total proficiency in all their languages.

This is also true for certain skills such as reading and writing. Many bilinguals do not need to read and write in some of their languages and hence have not developed these skills. Even if they do have reading and writing skills in their two or more languages, the levels of competence are probably different because the needs for these skills are not the same in each language.

Fortunately, researchers are starting to take the Complementarity Principle into account when describing language dominance. Carmen Silva-Corvalán of the University of Southern California and Jeanine Treffers-Daller of the University of Reading have just published a book on the topic and they give a new definition which takes into account the Principle: "... we define dominant language, a relative notion, as that in which a bilingual has attained an overall higher level of proficiency at a given age, and/or the language which s/he uses more frequently, and across a wider range of domains."

The book contains nine chapters by other researchers in addition to the ones by the editors, and it raises many unresolved issues relating to language dominance in children and adults. It also offers different theoretical perspectives on the question and a number of approaches to get at dominance. There is no doubt that it will very quickly become THE book to read on the topic!  

For a full list of "Life as a bilingual" blog posts by content area, see here.

Photo of a girl thinking from Shutterstock.


Wei, Li (2007). Dimensions of bilingualism. In Li Wei (ed), The Bilingualism Reader, pp. 3-24. London & New York: Routledge.

Silva-Corvalán, Carmen, and Treffers-Daller, Jeanine (2016). Language Dominance in Bilinguals: Issues of Measurement and Operationalization. Cambridge: Cambridge University Press.

Grosjean, François (2016). The Complementarity Principle and its impact on processing, acquisition, and dominance. In Carmen Silva-Corvalán & Jeanine Treffers-Daller (eds), Language Dominance in Bilinguals: Issues of Measurement and Operationalization. Cambridge: Cambridge University Press.

François Grosjean's website.

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