First language
First language (native language, mother tongue, or vernacular) is the language a person learns first. Correspondingly, the person is called a native speaker of the language, although one may also be a native speaker of more than one language, if all of the languages are learned naturally without formal instruction (i.e. through immersion) before puberty (see the discussion on multilingualism below). Often a child learns the basics of his or her first language(s) from his or her family.
Good skills in one's native language(s) are essential for further learning, as a native language is thought to be a base of thinking. Incomplete first language skills often make learning other languages difficult. Native language has therefore a central role in education.
The term "mother tongue" could be misleading. In some paternal societies, the wife moves in with the husband and thus may have a different first language (or dialect) than the local language of the husband. Yet their children usually only speak their local language. Only a few will learn to speak his or her mother's language like a native. Mother in this context probably originated from the definition of mother as source, or origin; as in mother-country or land.
One can have two (or more) native languages, thus being a native bilingual or indeed multilingual. The order in which these languages are learnt is not necessarily the order of proficiency. For instance, a French-speaking couple might have a daughter who learned French first, then English; but if she grew up in the United States, she is likely to become more proficient in English.
The Brazilian linguist Cleo Altenhofen considers the denomination "mother tongue" and its general usage not precise and leads to various interpretations that are biased in linguistic prejudices, specially when it comes to define which is the mother tongue of bilingual children from ethnical minority groups. He cites his own experience as a bilingual speaker of Portuguese language and Hunsrückish, a German-rooted language brought to Southern Brazil by the first German immigrants. In his case, similar to those of children who learn the language of the family which is different from the language of the environment (the 'official' language), it is questionable to say which language is his 'mother tongue'. Many scholars gave definitions of 'mother tongue' through the years based on the usage, the emotional relation from the speaker towards the language and even its dominance in relation to the environment, but all these criteria lack precision in linguistical terms.