You are assessing a patient's delusional belief and want to establish whether it is primary or secondary. Before revealing the answer, decide how you would explore its history.

Take a careful, chronological history of the belief's development, asking specifically what the patient's mood, perceptions, and other beliefs were like in the period immediately before it appeared. Ask whether the belief could plausibly be understood as growing out of something else — a period of depressed or elevated mood, a hallucinatory experience, or an existing idea that gradually escalated — or whether it instead simply appeared, in the patient's own account, as something entirely new. Bear in mind that a primary delusion is more often reported clearly in acute presentations, and can become harder to identify in chronic illness once it has been elaborated into a wider system of secondary delusions, so the history-taking may need to reach back to the earliest point the patient can recall.