Aphasia is an impairment of language, affecting the production or comprehension of speech and the ability to read or write. Aphasia is always due to injury to the brain. People with aphasia have difficulty with language, but they are not intellectually impaired.
For a discussion of the cultural and social significance of aphasia in the late nineteenth century, see Matt K. Matsuda, The Memory of the Modern, Oxford U. Press 1996. (pp 79-99)