Aphasia (or aphemia) 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. (Brookshire, 1992; Goodglass 1993) 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 or apraxia of speech, which also result from brain damage.

Prognosis
Aphasia can be assessed in a variety of ways, from quick clinical screening at the bedside to several-hour-long batteries of tasks that examine the key components of language and communication.

Diagnosis
Any of the following can be considered symptoms of aphasia:

inability to comprehend language
inability to pronounce, not due to muscle paralysis or weakness
inability to speak spontaneously
inability to form words
inability to name objects
poor enunciation
excessive creation and use of personal neologisms
inability to repeat a phrase
persistent repetition of phrases
paraphasia (substituting letters, syllables or words)
agrammatism (inability to speak in a grammatically correct fashion)
dysprosody (alterations in inflexion, stress, and rhythm)
uncompleted sentences
inability to read
inability to write Symptoms
The following table summarizes some major characteristics of different types of aphasia:

Types of aphasia
Classifying the different subtypes of aphasia is difficult and has led to disagreements among experts. The locationist model is the original model, but modern anatomical techniques and analyses have shown that precise connections between brain regions and symptom classification don't exist. The neural organization of language is complicated; language is a comprehensive and complex behavior and it makes sense that it isn't the product of some small, circumscribed region of the brain. No classification of patients in subtypes and groups of subtypes is adequate. Only about 60% of patients will fit in a classification scheme such as fluent/nonfluent/pure aphasias. There is a huge variation among patients with the same diagnosis, and aphasias can be highly selective. For instance, patients with naming deficits (anomic aphasia) might show an inability only for naming buildings, or people, or colors.

Classification of aphasia
The locationist model attempts to classify the aphasia by major characteristics and then link these to areas of the brain in which the damage has been caused. The initial two categories here were devised by early neurologists working in the field, namely Paul Broca and Carl Wernicke. Other researchers have added to the model, resulting in it often being referred to as the "Boston-Neoclassical Model". The most prominent writers on this topic have been Howard Goodglass and Edith Kaplan.

Individuals with Broca's aphasia (also termed expressive aphasia) were once thought to have ventral temporal damage though more recent work by Nina Dronkers using imaging and 'lesion analysis' has revealed that patients with Broca's Aphasia have lesions to the medial insular cortex. Broca missed these lesions because his studies did not disect the brains of diseased patients so only the more temporal damage was visible. Individuals with Broca's aphasia often have right-sided weakness or paralysis of the arm and leg because the frontal lobe is also important for body movement.
In contrast to Broca's aphasia, damage to the temporal lobe may result in a fluent aphasia that is called Wernicke's aphasia (also termed sensory aphasia). These individuals usually have no body weakness because their brain injury is not near the parts of the brain that control movement.
Working from Wernicke's model of aphasia, Ludwig Lichtheim proposed five other types of aphasia but these were not tested against real patients until modern imaging made more indepth studies available. The other five types of aphasia in the locationist model are:
Pure word deafness
Conduction aphasia
Apraxia of speech, which is now considered a separate disorder in itself.
Transcortical motor aphasia
Transcortical sensory aphasia
Anomia is another type of aphasia proposed under what is commonly known as the Boston-Neoclassical model, which is essentially a difficulty with naming. A final type of aphasia, global aphasia, results from damage to extensive portions of the language areas of the brain. The locationist model
The different types of aphasia can be divided into three categories: fluent, non-fluent and "pure" aphasias.

Fluent aphasias, also called receptive aphasias, are impairments related mostly to the input or reception of language, with difficulties either in auditory verbal comprehension or in the repetition of words, phrases, or sentences spoken by others. Speech is easy and fluent, but there are difficulties related to the output of language as well, such as paraphasia. Examples of fluent aphasias are: Wernicke's aphasia, Transcortical sensory aphasia, Conduction aphasia, Anomic aphasia
Nonfluent aphasias, also called expressive aphasias are difficulties in articulating, but in most cases there is relatively good auditory verbal comprehension. Examples of nonfluent aphasias are: Broca's aphasia, Transcortical motor aphasia, Global aphasia
"Pure" aphasias are selective impairments in reading, writing, or the recognition of words. These disorders may be quite selective. For example, a person is able to read but not write, or is able to write but not read. Examples of pure aphasias are: Alexia, Agraphia, Pure word deafness Fluent, non-fluent and "pure" aphasias
The cognitive neuropsychological model builds on cognitive neuropsychology. It assumes that language processing can be broken down into a number of modules, each of which has a specific function. Hence there is a module which recognises phonemes as they are spoken and a module which stores formulated phonemes before they are spoken. Use of this model clinically involves conducting a battery of assessments (usually from the PALPA), each of which tests one or a number of these modules. Once a diagnosis is reached as to where the impairment lies, therapy can proceed to treat the individual module.
A few less common subtypes include:
A combination of subtypes is possible.

Subcortical motor aphasia
Subcortical sensory aphasia
Mixed transcortical aphasia
Acquired eleptiform aphasia (Landau Kleffner Syndrome) The cognitive neuropsychological model
Aphasia can be divided into primary and secondary aphasia.

Primary aphasia is due to problems with language-processing mechanisms.
Secondary aphasia is the result of other problems, like memory impairments, attention disorders, or perceptual problems. Primary and secondary aphasia

Maurice Ravel
Jan Berry of Jan and Dean
Sven Nykvist
Ralph Waldo Emerson
Robert E. Lee
Joseph Chaikin
Sir John Hale Famous individuals who suffer(ed) from aphasia

Speech disorder
Dysnomia disorder Sources

R. Chapey (Ed.) (2001). Language Intervention Strategies in Aphasia and Related Neurogenic Communication Disorders (Fourth Edition). Philadelphia: Lippincott, Williams & Wilkins.
Goodglass, H. & Kaplan, E. (1972). Assessment of Aphasia and Related Disorders. Philadelphia: Lea and Febinger.
Kay, J., Lesser, R., & Coltheart, M. (1992). Psycholinguistic Assessments of Language Processing in Aphasia (PALPA). Hove: Erlbaum.
Spreen, O. & Risser, A.H. (2003). Assessment of Aphasia. New York: Oxford University Press.