Language acquisition refers both to the emergence of language in an individual and its study in linguistics. This term is often used interchangeably with language learning, but linguists sometimes distinguish them: acquisition involves intuitive, subconscious language development, whereas learning is more likely to consist of explicit, conscious attempts to grasp rules, perhaps in a classroom or through studying with a grammar book.
The study of language acquisition is commonly split between first (FLA) and second (SLA) language acquisition, the former considering the development of first languages (L1) in a child, the latter in adults who already have an L1. It should not be supposed that acquisition relates only to L1s, and learning to L2s; few linguists today argue that coming to a new or native language is fundamentally different depending on the individual's age. However, proponents of the critical period hypothesis maintain that biological differences remain between children and adults, claiming to account for the common perception that children's ultimate attainment in acquiring both first and subsequent languages is typically more complete that in adults.
Whereas the study of children's acquisition of language is mainly carried out by linguists and sometimes psychologists or speech therapists, SLA has expanded way beyond a purely theoretical, academic field. Applied linguistics concerns itself mainly with language learning, often in the classroom, and has developed its own theories which contrast with SLA; for example, applied linguists may focus more on the experiences, attitudes and approaches of the learner themselves, rather than on the actual system of language assumed to be common to all learners and contexts.