E. D. Hirsch's "Philosophy of Composition" (in press) reintroduces to communication theorists the "progress of language" thesis first developed, by Henry Bradley and Otto Jespersen around 1900, in the context of oral language. The thesis states that languages--English in particular--tend to become more simplified and flexible over time. This paper discusses recent investigations into the comprehension process as they relate to the progress-of-language thesis. While the investigations do not conclusively support the thesis, they do suggest parallels between historical and individual language development and between oral and written language. The paper describes aspects of comprehension common to both oral and written language, characteristics of the encoding of thought into speaking and writing, the appropriateness of extrapolating from studies about one form of language to another, and areas of research useful to the development of reading and writing in the young. A bibliography is attached. (RL)