information:filtering, information:classification
General approaches

A major debate in understanding language acquisition is how these capacities are picked up by infants from the linguistic input. Input in the linguistic context is defined as "All words, contexts, and other forms of language to which a learner is exposed, relative to acquired proficiency in first or second languages". Nativists such as Chomsky have focused on the hugely complex nature of human grammars, the finiteness and ambiguity of the input that children receive, and the relatively limited cognitive abilities of an infant. From these characteristics, they conclude that the process of language acquisition in infants must be tightly constrained and guided by the biologically given characteristics of the human brain. Otherwise, they argue, it is extremely difficult to explain how children, within the first five years of life, routinely master the complex, largely tacit grammatical rules of their native language. Additionally, the evidence of such rules in their native language is all indirect—adult speech to children cannot encompass all of what children know by the time they have acquired their native language.