proof of whether basic linguistic skills are innate (nature), acquired (nurture), or a combination of the two attributes. Cognitive approaches to SLA research deal with the processes in the brain that underpin language acquisition, for example how paying attention to language affects the ability to learn it, or how language acquisition is related to short-term memory and long-term memory. Sociocultural approaches reject the notion that SLA is a purely psychological phenomenon and attempt to explain it in a social context. Some key social factors that influence SLA are the level of immersion, connection to the L2 community, and gender. Linguistic approaches consider language separately from other kinds of knowledge and attempt to use findings from the wider study of linguistics to explain SLA. There is also a considerable body of research about how SLA can be affected by individual factors such as age and learning strategies. A commonly discussed topic regarding age in SLA is the critical period hypothesis, which suggests that individuals lose the ability to fully learn a language after a particular age in childhood. Another topic of interest in SLA is the differences between adult and child learners. Learning strategies are commonly categorized as learning or communicative strategies and are developed to improve their respective acquisition skills. Affective factors are emotional factors that influence an individual's ability to learn a new language. Common affective factors that influence acquisition are anxiety, personality, social attitudes, and motivation. In the domain of personality, introversion and extroversion in particular can affect learning. Individuals may also lose a language through a process called second-language attrition. This is often caused by a lack of use or exposure to a language over time. The severity of attrition depends on a variety of factors including level of proficiency, age, social factors, and motivation at the time of acquisition. Finally, classroom research deals with the effect that language instruction has on acquisition. Definitions Second language refers to any language learned in addition to a person's first language; although the concept is named second-language acquisition, it can also incorporate the learning of third, fourth, or subsequent languages. Second-language acquisition refers to what learners do; it does not refer to practices in language teaching, although teaching can affect acquisition. The term acquisition was originally used to emphasize the non-conscious nature of the learning process, but in recent years learning and acquisition have become largely synonymous. SLA can incorporate