What is mentalism/innatism ?

Mentalism/innatism is a theory that emphasizes innate/mental power to learn a language. Chomsky argues that human beings are biologically programmed to learn languages. He says that human brains contain a small device which is called Language Acquisition Device (LAD). This mental device helps children learn a language. This theory comes as opposed to the behaviorist theory,  which says that children learn from the environment. 

According to Chomsky,  children come with some principles of language learning,  such as sentence structures. Studies have shown that there are specific physical parts of the brain that are involved in receiving and producing language.  Second language acquisition theorists say that learners can learn second and subsequent languages if they are instructed properly by creating suitable conditions. This also suggests that language learners may develop competence if they are taught in natural communication and with authentic materials. As our brains are programmed to learn a language,  we just need some stimuli to do that. However, human beings do not learn a language by following instructions blindly; they make mistakes,  change structures,  and make their own sentences.