Global aphasia is the most severe form of aphasia. Patients with this form of aphasia produce few recognizable words and understand little or no spoken language. Global aphasics can neither read nor write. It is usually seen immediately after the patient has suffered a stroke and may improve quickly if the damage has not been too extensive. However, with greater brain damage, severe and lasting disability may result.

Broca's aphasia is often called 'non-fluent aphasia' because of the halting and effortful quality of the person's speech. Speech output is severely reduced and utterances are limited to less than six words. Vocabulary access is limited and the formation of sounds by persons with Broca's aphasia is often laborious and clumsy. The person may understand speech relatively well and be able to read, but be limited in their ability to write.

Mixed non-fluent aphasia occurs in patients who have sparse and effortful speech, resembling severe Broca's aphasia. However, unlike persons with Broca's aphasia, they remain limited in their comprehension of speech and do not read or write beyond an elementary level.

Wernicke's aphasia is also called 'fluent aphasia' because the individual is able to produce connected speech easily, but the main impairment is person's ability to grasp the meaning of spoken words. However, while the speech is produced easily, it is far from normal. Sentences do not hang together and irrelevant words (jargon) intrude in severe cases. Reading and writing are often severely impaired.

Anomic aphasia applies to persons who are left with a persistent inability to supply the words for the very things they want to talk about-particularly nouns and verbs. As a result their speech-- while fluent in grammatical form and output-- is full of vague circumlocutions and expressions of frustration. They understand speech well, and in most cases, read adequately. Difficulty finding words is as evident in writing as in speech.

In addition to the foregoing syndromes that are seen repeatedly by speech clinicians, there are many other possible combinations of deficits that do not exactly fit into these categories. Some of the components of a complex aphasia syndrome may also occur in isolation. This may be the case for disorders of reading (alexia) or disorders affecting both reading and writing (alexia and agraphia), following a stroke. Severe impairments of calculation (acalculia) often accompany aphasia, yet in some instances patients retain excellent calculation in spite of the loss of language.