Sensitive phases for language acquisition

Scrutinizing parallels and differences between first and second language acquisition has led us to the conclusion that some of the observable differences between these two acquisition types reflect different kinds of knowledge about formal properties of the respective target systems and result from different learning processes. These fundamental differences between L1 and L2 acquisition, I have argued, are due to the fact that the LAD does not operate in quite the same way in the two types of acquisition. It goes without saying that a complex and multifaceted process like language acquisition cannot be explained in terms of one factor or even one bundle of factors alone. In fact, variability within and across learners has been argued to be a defining characteristic of L2 acquisition, and this can be variability of knowledge as well as of how the knowledge is used (cf. Meisel, Clahsen and Pienemann 1981). Although the working of the LAD cannot be held accountable for all observed L1–L2 differences, there are good reasons to believe that it is the single most important cause for both similarities and differences.