Bilinguals are people who are fluent in two languages. It is not particularly necessary for bilinguals to be equally fluent in both languages. Fluency need not to be a binary classification but rather a continuum. While people often speak of first language or mother tongue and second language, psycholinguists refer to the language learned first as L1 and the language learned after that as L2. Sometimes the language learned second may become the primary language of use in everyday life and the language learned first may become the secondary language in later life. Bilingualism can also be categorised as follows:
- Simultaneous bilingualism: L1 and L2 learned simultaneously
- Early sequential bilingualism: L1 is learned first and L2 is learned in childhood
- Late sequential bilingualism: L1 is learned first and L2 is learned in adolescence or later
Bilingualism is not always a matter of choice. Some societies have a history of attempting to impose a language on others. In others, one language may be held as having higher prestige or allowing for better opportunities. On the other hand, bilingualism (or multilingualism) was the norm throughout most of human history until the rise of linguistically and ethnically divided states in Europe. Most human beings lived in multilingual societies or used one language in common use while learning another as a language of higher education (as with Latin in Europe, Sanskrit in India, Classical Chinese in China and English in the modern world).