Thought disorder is one of the most striking and debilitating aspects of severe psychosis. This refers to the way that thought is organized. Thought disorder does not pertain to the content of the thought process, to what the person is thinking about, but to the way that the ideas are put together. Does the person display a logical and orderly flow of ideas? Or are the ideas jumbled, only loosely related to each other and ultimately impossible to understand?

• Paucity of ideation refers to the lack of adequate thought content. The person’s mind is more or less blank.
• Overproduction of thought is the opposite condition, where ideas are tumbling out of the person’s mind.

Other terms refer specifically to the organization of the person’s thought and range in severity from mild and fairly normal to entirely incomprehensible.

• Digressive thought describes a state where the person drifts from topic to topic, but the speech is still understandable.
• Circumstantial thought is roundabout but eventually gets to the point. If you ask a circumstantial patient a question, he or she will go a long way around the point, but eventually answer the question.
• Tangential thought is more severe. With effort, you can understand the person, but it takes considerable concentration to identify the connections between the different ideas.
• Flight of Ideas is similar to tangential thought, but is also characterized by a highly energized overproduction of thought.
• Looseness of association is not intelligible. Fragments of ideas may be recognizable, but the person can lapse into a loose stream of thoughts in which separate ideas bear little relationship to one another.
• Word salad is essentially gibberish, with no clear relationship between the words in the sentence.

While thought disorder can be present in many psychiatric illnesses, severe thought disorder is most characteristic of schizophrenia.