First language

A first language (also native language, father tongue/mother tongue, arterial language, or L1) is a language that a person has been exposed to from birth or within the critical period. If there are multiple L1, the designation "first language" is used for the L1 spoken the best or the one that is the basis for sociolinguistic identity. In some countries, the term native language or mother tongue refers to the language of one's ethnic group rather than one's first language. Children brought up speaking more than one language can have more than one native language, and be bilingual.

By contrast, a second language is any language that one speaks other than one's first language.

One of the more widely accepted definitions of native speakers is that they were born in a particular country raised to speak the language of that country during the critical period of their development, The person qualifies as a "native speaker" of a language by being born and immersed in the language during youth, in a family in which the adults shared a similar language experience as the child. Native speakers are considered to be an authority on their given language because of their natural acquisition process regarding the language, as opposed to having learned the language later in life. That is achieved by personal interaction with the language and speakers of the language. Native speakers will not necessarily be knowledgeable about every grammatical rule of the language, but they will have good "intuition" of the rules through their experience with the language.

Sometimes, the term mother tongue or mother language is used for the language that a person learned as a child at home (usually from their parents). Children growing up in bilingual homes can, according to this definition, have more than one mother tongue or native language.

In the context of population censuses conducted on the Canadian population, Statistics Canada defines mother tongue as "the first language learned at home in childhood and still understood by the individual at the time of the census." It is quite possible that the first language learned is no longer a speaker's dominant language. That includes young immigrant children whose families have moved to a new linguistic environment as well as people who learned their mother tongue as a young child at home (rather than the language of the majority of the community), who may have lost, in part or in totality, the language they first acquired (see language attrition).

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