Formal thought disorder refers to disorganised thinking as evidenced in speech. They are especially associated with schizophrenia and psychosis.

Types

Circumstantiality - The patient moves onto different topics but there is a train of thought that can be followed. They eventually return to the original topic.

Derailment/knights move - The conversation moves randomly from one topic to another.

Poverty of speach - A lack of spontaneous speech.

Perseveration - The repetition of words or ideas when another person attempts to change the topic.

Thought blocking - The patient suddenly halts in their thought process and cannot continue.