Paraphasia is associated with fluent aphasias, characterized by “fluent spontaneous speech, long grammatically shaped sentences and preserved prosody abilities.” Examples of these fluent aphasias include receptive or Wernicke’s aphasia, anomic aphasia, conduction aphasia, and transcortical sensory aphasia, among others. All of these lead to a difference in processing efficiency, which is often caused by damage to a cortical region in the brain (in receptive aphasia, for example, the lesion is in or near Wernicke’s area); lesion location is the most important determining factor for all aphasic disorders, including paraphasia - the location of the lesion can be used to hypothesize the type of aphasic symptoms the patient will display. This lesion can be caused by a variety of different methods: malfunctioning blood vessels (caused, for example, by a stroke) in the brain are the cause of 80% of aphasias in adults, as compared to head injuries, dementia and degenerative diseases, poisoning, metabolic disorders, infectious diseases, and demyelinating diseases. Lesions involving the posterior superior temporal lobe are often associated with fluent aphasias.

Two areas of the brain, Broca’s area and Wernicke’s area, are responsible for various disruptions in speech when damaged. Each is defined by their distinct characteristics. Broca’s aphasia is characterized by non-fluent or telegraphic-type speech - where articles, conjunctions, prepositions, auxiliary verbs, pronouns and morphological inflections (plurals, past tense) are omitted. The word substitutions are infrequent and distortion of consonants and simplification of consonant clusters is frequent. Content words such as nouns, verbs and adjectives may be preserved. Subjects of this aphasia are aware of their errors in speech. Damage to the Broca’s area does not affect comprehension of speech.

Wernicke’s aphasia is characterized by fluent language with made up or unnecessary words with little or no meaning to speech. Those who suffer from this type of aphasia have difficulty understanding others speech and are unaware of their own mistakes. When corrected they will repeat their verbal paraphasias and have trouble finding the correct word. Wernicke’s aphasia is found in the dominant hemisphere of the posterior gyrus of the first temporal convolution of the brain, whereas Broca’s aphasia is found anterior to the Wernicke’s area.

Given the previously stated signs and symptoms the following behaviors are often seen in people with aphasia as a result of attempted compensation for incurred speech and language deficits:

- Self-repairs: Further disruptions in fluent speech as a result of mis-attempts to repair erred speech production.

- Speech disfluencies: Include previously mentioned disfluencies including repetitions and prolongations at the phonemic, syllable and word level presenting in pathological/ severe levels of frequency.

- Struggle in non-fluent aphasias: A severe increase in expelled effort to speak after a life where talking and communicating was an ability that came so easily can cause visible frustration.

- Preserved and automatic language: A behavior in which some language or language sequences that were used so frequently, prior to onset, they still possess the ability to produce them with more ease than other language post onset.

People with aphasia may experience any of the following behaviors due to an acquired brain injury, although some of these symptoms may be due to related or concomitant problems such as dysarthria or apraxia and not primarily due to aphasia. Aphasia symptoms can vary based on the location of damage in the brain. Signs and symptoms may or may not be present in individuals with aphasia and may vary in severity and level of disruption to communication. Often those with aphasia will try to hide their inability to name objects by using words like "thing". So when asked to name a pencil they may say it is a thing used to write.

- 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 (anomia)

- Poor enunciation

- Excessive creation and use of personal neologisms

- Inability to repeat a phrase

- Persistent repetition of one syllable, word, or phrase (stereotypies)

- Paraphasia (substituting letters, syllables or words)

- Agrammatism (inability to speak in a grammatically correct fashion)

- Dysprosody (alterations in inflexion, stress, and rhythm)

- Incomplete sentences

- Inability to read

- Inability to write

- Limited verbal output

- Difficulty in naming

- Speech disorder

- Speaking gibberish

- Inability to follow or understand simple requests

Transcortical sensory aphasia (TSA) is a kind of aphasia that involves damage to specific areas of the temporal lobe of the brain, resulting in symptoms such as poor auditory comprehension, relatively intact repetition, and fluent speech with semantic paraphasias present. TSA is a fluent aphasia similar to Wernicke's aphasia, with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia").

In all of these ways, TSA is very similar to a more commonly known language disorder, receptive aphasia. However, transcortical sensory aphasia differs from receptive aphasia in that patients still have intact repetition and exhibit echolalia, or the compulsive repetition of words. Transcortical sensory aphasia cannot be diagnosed through brain imaging techniques such as functional magnetic resonance imaging (fMRI), as the results are often difficult to interpret. Therefore, clinicians rely on language assessments and observations to determine if a patient presents with the characteristics of TSA. Patients diagnosed with TSA have shown partial recovery of speech and comprehension after beginning speech therapy. Speech therapy methods for patients with any subtype of aphasia are based on the principles of learning and neuroplasticity. Clinical research on TSA is limited because it occurs so infrequently in patients with aphasia that it is very difficult to perform systematic studies.

TSA should not be confused with transcortical motor aphasia (TMA), which is characterized by nonfluent speech output, with good comprehension and repetition. Patients with TMA have impaired writing skills, difficulty speaking and difficulty maintaining a clear thought process. Furthermore, TMA is caused by lesions in cortical motor areas of the brain as well as lesions in the anterior portion of the basal ganglia, and can be seen in patients with expressive aphasia.

Naming involves the ability to recall an object. Patients with TSA, as well as patients with all other aphasia subtypes, exhibit poor naming. Clinical assessment of naming involves the observer first asking the patient to name high frequency objects such as clock, door, and chair. TSA patients who name common objects with ease generally have difficulty naming both uncommon objects and specific parts of objects such as lapel, or the dial on a watch.

Paragrammatism is the confused or incomplete use of grammatical structures, found in certain forms of speech disturbance. Paragrammatism is the inability to form grammatically correct sentences. It is characteristic of fluent aphasia, most commonly Receptive aphasia. Paragrammatism is sometimes called "extended paraphasia," although it is different from paraphasia. Paragrammatism is roughly synonymous with "word salad," which concerns the semantic coherence of speech rather than its production.

The main clinical features are signature language progressive difficulties with speech production. There can be problems in different parts of the speech production system, hence patients can present with articulatory breakdown, phonemic breakdown (difficulties with sounds) and other problems. However, it is rare for patients to have just one of these problems and most people will present with more than one problem. Features include:

- Hesitant, effortful speech

- Speech 'apraxia'

- Stutter (including return of a childhood stutter)

- Anomia

- Phonemic paraphasia (sound errors in speech e.g. 'gat' for 'cat')

- Agrammatism (using the wrong tense or word order)

As the disease develops, speech quantity decreases and many patients will become mute.

Cognitive domains other than language are rarely affected early on. However, as the disease progresses other domains can be affected. Problems with writing, reading and speech comprehension can occur as can behavioural features similar to frontotemporal dementia.

There is some confusion in the terminology used by different neurologists. Mesulam's original description in 1982 of progressive language problems caused by neurodegenerative disease (which he called primary progressive aphasia (PPA) included patients with progressive non-fluent (PNFA), semantic dementia (SD), and logopenic progressive aphasia (LPA).

Huber assumes a disturbance of the sequential organization of sentences as the cause of the syntactic errors (1981:3). Most students and practitioners regard paragrammatism as the morphosyntactic "leitsymptom" of Wernicke’s aphasia.

However, ever since the introduction of the term paragrammatism some students have

pointed out that paragrammatic and agrammatic phenomena, which in classical theory form

part of Broca’s aphasia, may co-occur in the same patient.

In considering whether an individual has thought disorder, patterns of their speech are closely observed. Although it is normal to exhibit some of the following during times of extreme stress (e.g. a cataclysmic event or the middle of a war) it is the degree, frequency, and the resulting functional impairment that leads to the conclusion that the person being observed has a thought disorder.

- "Alogia" (also "poverty of speech") – A poverty of speech, either in amount or content; it can occur as a negative symptom of schizophrenia.

- "Blocking" – An abrupt stop in the middle of a train of thought; the individual may or may not be able to continue the idea. This is a type of formal thought disorder that can be seen in schizophrenia.

- "Circumstantiality" (also "circumstantial thinking", or "circumstantial speech") – An inability to answer a question without giving excessive, unnecessary detail. This differs from tangential thinking, in that the person does eventually return to the original point.

- "Clanging" or "Clang association" – a severe form of flight of ideas whereby ideas are related only by similar or rhyming sounds rather than actual meaning. This may be heard as excessive rhyming and/or alliteration. e.g. "Many moldy mushrooms merge out of the mildewy mud on Mondays." "I heard the bell. Well, hell, then I fell." It is most commonly seen in bipolar affective disorder (manic phase), although it is often observed in patients with primary psychoses, namely schizophrenia and schizoaffective disorder.

- "Derailment" (also "loose association" and "knight's move thinking") – Thought and/or speech move, either spontaneously or in response to an internal stimulus (distinguishing derailment from "distractible speech," "infra"), from the topic's track onto another which is obliquely related or unrelated. e.g. "The next day when I'd be going out you know, I took control, like uh, I put bleach on my hair in California."

- "Distractible speech" – During mid speech, the subject is changed in response to an external stimulus. e.g. "Then I left San Francisco and moved to... where did you get that tie?"

- "Echolalia" – Echoing of another's speech that may only be committed once, or may be continuous in repetition. This may involve repeating only the last few words or last word of the examiner's sentences. This can be a symptom of Tourette's Syndrome. e.g. "What would you like for dinner?", "That's a good question. "That's a good question". "That's a good question". "That's a good question"."

- "Evasive interaction" – Attempts to express ideas and/or feelings about another individual come out as evasive or in a diluted form, e.g.: "I... er ah... you are uh... I think you have... uh-- acceptable erm... uh... hair."

- "Flight of ideas" – a form of formal thought disorder marked by abrupt leaps from one topic to another, albeit with discernable links between successive ideas, perhaps governed by similarities between subjects or, in somewhat higher grades, by rhyming, puns, and word plays (clang associations), or innocuous environmental stimuli – e.g., the sound of birds chirping. It is most characteristic of the manic phase of bipolar illness.

- "Illogicality" – Conclusions are reached that do not follow logically (non-sequiturs or faulty inferences). e.g. "Do you think this will fit in the box?" draws a reply like "Well duh; it's brown, isn't it?"

- "Incoherence (word salad)" – Speech that is unintelligible because, though the individual words are real words, the manner in which they are strung together results in incoherent gibberish, e.g. the question "Why do people comb their hair?" elicits a response like "Because it makes a twirl in life, my box is broken help me blue elephant. Isn't lettuce brave? I like electrons, hello please!"

- "Loss of goal" – Failure to follow a train of thought to a natural conclusion. e.g. "Why does my computer keep crashing?", "Well, you live in a stucco house, so the pair of scissors needs to be in another drawer."

- "Neologisms" – New word formations. These may also involve elisions of two words that are similar in meaning or in sound. e.g. "I got so angry I picked up a dish and threw it at the geshinker."

- "Perseveration" – Persistent repetition of words or ideas even when another person attempts to change the topic. e.g. "It's great to be here in Nevada, Nevada, Nevada, Nevada, Nevada." This may also involve repeatedly giving the same answer to different questions. e.g. "Is your name Mary?" "Yes." "Are you in the hospital?" "Yes." "Are you a table?" "Yes." Perseveration can include palilalia and logoclonia, and can be an indication of organic brain disease such as Parkinson's.

- "Phonemic paraphasia" – Mispronunciation; syllables out of sequence. e.g. "I slipped on the lice and broke my arm."

- "Pressure of speech" – Unrelenting, rapid speech without pauses. It may be difficult to interrupt the speaker, and the speaker may continue speaking even when a direct question is asked.

- "Self-reference" – Patient repeatedly and inappropriately refers back to self. e.g. "What's the time?", "It's 7 o'clock. That's my problem."

- "Semantic paraphasia" – Substitution of inappropriate word. e.g. "I slipped on the coat, on the ice I mean, and broke my book."

- "Stilted speech" – Speech characterized by the use of words or phrases that are flowery, excessive, and pompous. e.g. "The attorney comported himself indecorously."

- "Tangentiality" – Wandering from the topic and never returning to it or providing the information requested. e.g. in answer to the question "Where are you from?", a response "My dog is from England. They have good fish and chips there. Fish breathe through gills."

- "Word approximations" – Old words used in a new and unconventional way. e.g. "His boss was a ."

The concept of thought disorder has been criticized as being based on circular or incoherent definitions. For example, thought disorder is inferred from disordered speech, based on the assumption that disordered speech arises because of disordered thought. Incoherence, or word salad, refers to speech that is unconnected and conveys no meaning to the listener.

Furthermore, although thought disorder is typically associated with psychosis, similar phenomena can appear in different disorders, potentially leading to misdiagnosis—for example, in the case of incomplete yet potentially fruitful thought processes.

It has been suggested that individuals with autism spectrum disorders (ASD) display language disturbances like those found in schizophrenia; a 2008 study found that children and adolescents with ASD showed significantly more illogical thinking and loose associations than control subjects. The illogical thinking was related to cognitive functioning and executive control; the loose associations were related to communication symptoms and to parent reports of stress and anxiety.