If you are looking for an answer to that title, let me tell you straight away, this article is not going to tell you. Recently, however, there has been an (alarming) number of articles and posts on the internet, aimed at parents raising mutlilingual children, claiming that a child needed to be exposed to, on average, a minimum of 30% of their awake time to the minority language in order for him/her to be able to use that language. Now, I am not disputing the fact that there may be a cut-off point below which acquiring the language may be difficult beyond the use of a few basic words by the child. But there are so many things wrong with this statement that I feel it is a very dangerous one to present to parents. But, let me come back to the statement and its origins first. The myth The various versions of this myth claim that "a child needs to be exposed to a language for a minimum of 30% of the time spent awake in order to start (and continue) using the language actively" or that "20% input is the minimum for successful language acquisition" or that "less than 20 hours may make it difficult for the minority language to keep pace". The origins of the myth As a researcher, I cannot help but think that quoting this number because someone else quoted it is not proof enough that it holds any truth. I need scientific evidence. It seems that this statement could have originated from a misquote from Fred Genesee, a Canadian leading academic in terms of bilingual language acquisition. What Genesee actually stated is that when his team of researcher choose participants for their studies on bilingual acquisition, they choose children who are exposed to at least 30% of their minority language. It is a decision they have to make to ensure the children are growing up bilinguals. A lot of other research teams use a similar selection point. Pearson's research team, for example, uses 20% as a cut-off point and she mentions it in her Raising a bilingual child book (p. 116). What they did NOT say, however, is that you needed to be exposed to at least 30% of your minority language to be bilingual or to acquire it or that it should be a target for families. Big difference, in my opinion. What is wrong with this myth As I mentioned before, there are many things wrong with this claim. - How can you accurately measure exposure time? How about thinking time, quiet time, play time when we are not around to overhear? How can you make sure when you read to your child in English, he or she is not thinking in their other language and translating in their head? LJ spends 2 hours in the morning before going to kindergarten with me and her father. I speak to her in French, her dad speaks in Portuguese (with some English) and as a couple we speak English. How on earth do I quantify that? Would you have to count words we produce? - How about trilinguals or quadrilinguals? My daughter stands no chance with this myth. She is exposed to 4 languages and mathematically, if she had a perfectly balanced exposure, she would get 25% in each language, leaving her little chance according to this myth. Now, even if I can quantify her input approximately, I could come up to the conclusion that she is exposed to French about 30% of the time and less of the other languages. Her German clearly stands little chance then (and let's not even mention her Portuguese or English). Yet, I cannot help but feel that her German is growing faster than any of her other languages at the moment. planting seeds for the future - What ages are we talking about in this myth? It is unclear. Genesee and Pearson tend to work with very young bilinguals (somewhere between 6 months and 5 years old). I am not sure they would apply the same criteria to older kids. - How long for? Until what age, should we have this balance of languages? How do we measure it over time? Life is rather unpredictable and language balance often shifts over time and at different times of our lives as we move country, start school, get a job, etc. - What are the languages used for? Different languages of a multilingual are used for different purposes. We may not need the same amount of exposure or type of exposure to each language. After all, does it matter that my daughter is only exposed to 11% (I am making this up) of her awake time to Portuguese? All she needs it for is to talk to her Grandma over Skype once a week and for a holiday once a year. She may understand enough for that. What scientific evidence tells us The truth is there is very little scientific evidence about minimum exposure time in bilingual children (and even less, if any at all, for multilingual kids). Almost all of the evidence on the topic is anecdotal. First of all, the research evidence indicates quite clearly that the reduced input that results from exposure to two languages during the preschool years does not impact certain aspects of language development in simultaneous bilingual (grammar, for example). One of the only studies, to my knowledge, on the topic is that of Thordardottir (2011). She suggests that bilingual children need at least 40% of waking hour exposure to a language if their competence in that language (as measured by words production and comprehension) is to be comparable to that of monolingual children, WHEN assessed using standardized tests. But this not even true for all aspects of words acquisition they studied. However, even under optimal conditions (50:50), a bilingual's languages may differ from that of a monolingual because their communicative needs are different. A bilingual almost certainly uses their languages for different purposes. PIN me to save I will end the topic with this quote from F. Grosjean (found here): there is no good measure of “enough exposure” We really need to stop comparing multilinguals to monolinguals as if these are the reference and multilingualism is a disorder!! So, stop obsessing about numbers and remember that the seed planted may take time to grow, but it is there and can be reactivated with a little water, nutrients and care whenever needed. I would like to thank Madalena Cruz-Ferreira for sharing her views on the issue with me. I am solely responsible for everything written here though. Thordardottir, E. (2011). The relationship between bilingual exposure and vocabulary development, International Journal of Bilingualism, 15,4, 426-44.