What is typical language development?

In light of Musolino, Chunyo and Landau’s findings and conclusions regarding syntax comprehension in Williams syndrome (this issue), we review the criteria used to determine whether the development of language is typical or atypical and our current understanding of the causes of language delay. Given a certain set of theoretical assumptions (e.g., generative / modular), fairly poor performance can nevertheless be viewed as indicating typical development. Given other theoretical assumptions (e.g., a neuroconstructivist view of constrained development), the same data can be viewed as indicative of atypicality.