Bilingualism is the use of two languages by an individual or within a community. It is the most common human linguistic condition; monolingualism is the exception globally, not the norm.
| Type | Definition |
|---|---|
| Simultaneous | Two languages acquired from birth (bilingual first language acquisition) |
| Sequential/successive | L2 acquired after L1 is established (early or late) |
| Balanced | Equal proficiency in both languages; rare in practice |
| Dominant | Greater proficiency in one language; dominance shifts by domain and life stage |
| Receptive/passive | Can understand but not produce the second language |
Balanced bilingualism, equal facility in all domains in both languages, is an idealisation. In reality, bilinguals typically use each language in different domains (home, work, education, religion) and their proficiency varies accordingly. A Vietnamese-English bilingual may be dominant in Vietnamese for family topics but dominant in English for academic discourse.
A community or society where two languages are in regular use. This may involve:
Lambert (1974) distinguished two outcomes:
The distinction is critical for education policy: immersion programmes work additively when the L1 is socially strong (e.g., English speakers learning French in Canada) but may work subtractively when the L1 is already threatened (e.g., indigenous language speakers in English-medium schools).
Research since Peal & Lambert (1962) has shown cognitive advantages for bilinguals:
However, the "bilingual advantage" in executive function has been debated, with some studies failing to replicate the effect (Paap & Greenberg 2013). The metalinguistic advantage is more robust.
Cummins (1979, 1984) proposed the threshold hypothesis, which holds that a minimum level of L2 proficiency is needed for cognitive benefits, and the interdependence hypothesis, which holds that academic skills transfer across languages. See BICS and CALP.