In the field of second language acquisition (SLA), we investigate how people learn new languages later in life, that is, after the critical period when children learn their first language(s) (read our section Child language*). Similar to first language acquisition, timing is considered a critical factor in the achievement of SLA. In SLA, we usually look at the outcomes of those who learn new languages in their ‘late childhood’ and those in ‘adulthood’.
In addition to age, a range of other factors involved in the process of learning is also of linguists’ interest. That includes teachers’ strategies (e.g., how teachers correct errors), learners’ strategies (e.g., how learners overcome problems), learners’ cognitive competence (e.g., whether they are capable of noticing errors), and other less studied aspects like learning motivation, aptitude and personality.
Learning settings may influence SLA outcomes largely, too. For example, one who learns a language only in the classroom (‘foreign language’ setting) may be good at grammar but not so much at speaking with native speakers of the target language. In comparison, one who learns in the natural environment filled with the target language (‘second language’ setting) may be able to carry out more fluent conversation. The differences are related to what kind of ‘input’ a learner receives and what kind of ‘output’ he/she produces while learning. The amounts of ‘input’ and ‘output’ throughout learning may also matter a lot.
To assess an SLA learner’s level of proficiency, we investigate the acquisition of all aspects of linguistic competence, including pronunciation, vocabulary, grammar, pragmatics and so on. Sometimes we assess learners with proficiency tests that include different levels of listening and reading comprehension tasks. As to examine leaners’ output, either writing or speaking, we usually look at their ‘accuracy’, ‘complexity’ (e.g., in terms of grammatical structures) and ‘fluency’.
Due to its nature of applying linguistic knowledge to practical use, SLA is usually considered a subfield of applied linguistics. It usually incorporates perspectives of education, psychology and sociology. Findings in SLA are ultimately expected to contribute to improving language teaching and learning.
Video: There are many successful language learners and polyglots out there who are willing to share their experience and strategies of learning multiple second languages. But remember—not every method suits every learner. The TED talk by language teacher Sid Efromovich is just an example that you may be able to learn something from: 5 techniques to speak any language.