The Continuing Relevance of Cause

Leonard proposes that many language-impaired children simply represent the low end of the normal distribution of language ability, and further, that this fact has significant research implications. His proposal does not eliminate neuropathology as one possible primary cause of language impairment, nor does it deny the reality of physical differences between children who do and do not learn language easily. Given current trends in population definition, Leonard’s vision of the normal, language-impaired child, seems plausible. Such children may not welcome etiologically oriented research, but they still invite questions about proximal causal mechanisms. Continued research into such causes should illuminate both the nature of the impairment and the nature of language learning.