About Aphasia

What is aphasia?
Aphasia is a loss of the ability to produce and/or comprehend language, due to injury to brain areas specialized for these functions. It is not a result of deficits in sensory, intellect, or psychiatric functioning. It is also not muscle weakness or a cognitive disorder.

Depending on the area and extent of the damage, someone suffering from aphasia may be able to speak but not write, or vice versa, or display any of a wide variety of other deficiencies in language comprehension and production, such as being able to sing but not speak. Aphasia may co-occur with speech disorders such as dysarthria (poor articulation) or apraxia of speech (impaired ability to coordinate the sequential, articulatory movements necessary to generate speech sounds), which also result from brain damage.

Link: About Aphasia.