What is the difference between a first, second and heritage language?

How and when a language was acquired, and in what environment — distinctions that matter because they predict very different patterns of ability.

First language (L1, native language, mother tongue). Acquired in early childhood without formal instruction, through exposure. Characterised by complete, effortless grammatical competence and native pronunciation. A person can have more than one — simultaneous bilinguals acquiring two languages from infancy have two first languages, not one and a half.

Second language (L2). Learned after a first language is established, whether in childhood or adulthood, and whether through instruction or immersion. "Second" is conventional, not numerical — a fourth language learned is still an L2 in this sense.

The technical distinction between second and foreign language: a second language is learned in an environment where it is widely spoken; a foreign language is learned where it is not. The difference in available input is substantial.

Heritage language. The interesting and frequently misunderstood case. A language acquired at home in childhood, in a community where a different language dominates — typically the language of immigrant parents.

The characteristic profile: strong pronunciation, frequently indistinguishable from a native speaker; good comprehension, especially of everyday domestic speech; and uneven production — vocabulary concentrated in home and family domains, with gaps in academic, professional or formal registers; sometimes limited literacy; and grammar that diverges from the standard in specific, patterned ways.

This produces a mismatch that causes real difficulty: heritage speakers sound fluent, so listeners expect full competence and are surprised by gaps. They are frequently misplaced in language classes designed either for beginners, which is insultingly basic, or for advanced learners, which assumes literacy they may not have. Dedicated heritage language courses exist for this reason.

Language attrition is the related phenomenon — losing competence in a language through disuse, which can affect a first language after long immersion elsewhere.

Receptive bilingualism describes understanding a language well while speaking it little, common in second-generation communities.