Affective factors definitely play a role in second language acquisition, research has confirmed that a variety of affective variables relate to success in second language acquisition.
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The critical period hypothesis was first proposed by Montreal neurologist Wilder Penfield and co-author Lamar Roberts in their 1959 book Speech and Brain Mechanisms, and was popularized by Eric Lenneberg …
An interlanguage is the term for a dynamic linguistic system that has been developed by a learner of a second language (or L2) who has not become fully proficient
This video explains what Universal Grammar is in Simple Terms