Rethinking disorders of spoken and written language: generating workable hypotheses.

Disorders of spoken and written language (DSWL) tend to overlap at multiple levels: manifestationally, procedurally, developmentally, and etiologically. In other words, these disorders exhibit a positive manifold of correlations expressed among their different procedural components and in prospective, concurrent, and retrospective comorbidity. There is no single accepted explanation for this positive manifold of correlations. The purpose of this article is to explore this multilayer overlap and to consider whether such a positive manifold can be explained by one or all of the three hypotheses delineated in the article.