第15页 the role of social experience

Not all of L1 acquisition can be attributed to innate ability, for language-specific learning also plays a crucial role.
Appropriate social experience, including L1 input and interaction,
is thus a necessary condition for acquisition.
As long as children are experiencing adequate L1 input and interaction
from people around them, the rate and sequence of their phonological
and grammatical development does not appear to vary systematically
according to its source,
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vocabulary is typically learned in conjunction with social experiences