Circumstantiality: overly detailed speech with eventual return to the topic of focus after many digressions.Schizophrenia, dementia

Tangentiality: continuous diversion from the topic of focus with no return to it.

Looseness of associations: continuing change of topic with only loose associations between topics.

Derailment: a sequence of completely unrelated thoughts with change of frame of reference between sentences.

Flight of ideas: jumping from topic to topic with no discernable associations.Acute mania

Word salad: an incoherent mix of words and phrases.Wernicke's area lesion, dementia, schizophrenia

Thought blocking: sudden cessation of speech in the middle of a thought followed by silence.

Clang associations: thoughts connected by association of similar sounds (e.g. compulsive rhyming).

Perseveration: continued repetition of a word or phrase after it is no longer appropriate to respond in this way. For example, the patient may correctly answer 'Monday' when asked the day of the week and then answer all further questions with 'Monday'.

Neologisms: the formation of new words.