Bilingualism and multilingualism can be classified in several ways. No single scheme captures every multilingual biography.
By time and mode of acquisition
- Simultaneous bilingualism: two languages are acquired from very early childhood.
- Sequential bilingualism: another language is acquired after the first has already begun to develop.
- Late bilingualism: another language is acquired later in adolescence or adulthood.
By linguistic competence
A distinction is often made between dominant bilingualism and balanced bilingualism. Perfectly balanced bilingualism is rare because equal competence in every domain, register and skill would be an exceptionally demanding criterion.
Additive and subtractive bilingualism
In an additive situation, a new language expands the repertoire without displacing the existing language. In a subtractive situation, social pressure and changing use can weaken or replace the earlier language.
These classifications are analytical tools. Real biographies often combine several categories and change over time.