Thought disorder

# Overview
Thought disorder or formal thought disorder is a term used to describe a pattern of disordered language use that is presumed to reflect disordered thinking. It is usually considered a symptom of psychotic mental illness, although it occasionally appears in other conditions.
It describes a persistent underlying disturbance to conscious thought and is classified largely by its effects on speech and writing. Affected persons may show pressure of speech (speaking incessantly and quickly), derailment or flight of ideas (switching topic mid-sentence or inappropriately), thought blocking, rhyming, punning, or 'word salad' when individual words may be intact but speech is incoherent.
Eugen Bleuler, who named schizophrenia, held that its defining characteristic was a disorder of the thinking process. It is important to note however that the delusions and hallucinations of psychosis could also be considered as disorders of thought, but that the term formal thought disorder applies specifically to the presumed disruption in the flow of conscious verbal thought that is inferred from spoken language. This is typically what is referred to when the strictly less accurate, more commonly used but abbreviated term, 'thought disorder', is used.

# Specific subtypes in detail
Nancy C. Andreasen has given the following definitions.
- Pressure of speech - An increase in the amount of spontaneous speech compared to what is considered customary.
- Distractible speech - During mid speech, the subject is changed in response to a stimulus. e.g. "Then I left San Francisco and moved to... where did you get that tie?"
- Tangentiality - Replying to questions in an oblique, tangential or irrelevant manner. e.g:
- Derailment/Loose Association (Knight's move thinking) - Ideas slip off the track on to 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."
- Incoherence (word salad) - Speech that is unintelligible due to the fact that, 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 believe in God?" elicits a response like "Because he makes a twirl in life, my box is broken help me blue elephant. Isn't lettuce brave?  I like electrons. Hello, beautiful."
- Illogicality - Conclusions are reached that do not follow logically (non sequiturs or faulty inductive inferences). e.g. "Do you think this will fit in that box?" draws a reply like "Well duh; it's brown, isnt it?"
- Clanging - Sounds rather than meaningful relationships appear to govern words. e.g. "I'm not trying to make noise. I'm trying to make sense. If you can't make sense out of nonsense, well, have fun."
- Neologisms - New word formations. e.g. "I got so angry I picked up a dish and threw it at the geshinker."
- Word approximations - Old words used in a new and unconventional way. e.g. "His boss was a seeover."
- Circumstantiality - Speech that is very delayed at reaching its goal. Excessive long windedness. e.g. "What is your name?" "Well, sometimes when people ask me that I have to think about whether or not I will answer because some people think it's an odd name even though I dont really because my mom gave it to me and I think my dad helped but it's as good a name as any in my opinion but yeah it's Tom."
- Loss of goal - Failure to show a chain 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."
- Perseveration - Persistent repetition of words or ideas. e.g. "I'll think I'll put on my hat, my hat, my hat, my hat, my hat..."
- Echolalia - Echoing of one's or other people's speech that may only be commited once, or may be continuous in repetition 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."
- Blocking - Interruption of train of speech before completion. e.g. "Am I early?", "No, you're just about on-"
- Stilted speech - Speech excessively stilted and formal. e.g. "The attorney comported himself indecorously."
- 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."
- Phonemic paraphasia - Mispronunciation; syllables out of sequence. e.g. "I slipped on the lice broke my arm."
- Semantic paraphasia - Substitution of inappropriate word. e.g. "I slipped on the coat, on the ice I mean, and broke my book."

# Diagnostic issues
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, however it is assumed that disordered speech arises because of disordered thought. Similarly the definition of 'Incoherence' (word salad) is that speech is incoherent.
Furthermore, although thought disorder is typically associated with psychosis, similar phenomena can appear in different disorders, potentially leading to misdiagnosis.
For example, people with Asperger syndrome often are noted for having a highly pedantic way of speaking, using language far more formal and structured than the situation normally would be thought to call for. Language abnormalities in Asperger Syndrome include literalness, substitutions, monotonous speech, repetition (echolalia), staccato speech, narrow focus on the details and obsessive questions. A tendency to misdirect the conversation toward the person's obsessional interest could be mistaken for evidence of associative loosening. A comparison between autism and schizophrenia showed that they did not differ in degree of affective blunting, and that people with autism showed poverty of speech, poverty of content of speech and perseveration. However, the autism group showed much less derailment and illogicality, due to their often obsessive focus on special topics of interests.
Many people with Asperger syndrome also make idiosyncratic use of words, including coinages and unusual juxtapositions. This can develop into a rare gift for humor (especially puns, wordplay, doggerel, satire) or writing. Tony Attwood refers to a particular child's skill at inventing expressions, e.g. "tidying down" (the opposite of tidying up) or "broken" (when referring to a baby brother who cannot walk or talk) (Attwood, 82). Another noted behavioral characteristic that may be present is echolalia, which causes the subject to repeat words, or parts of words, when they speak, like an echo, or palilalia repeating one's own words (Attwood, 109).