A man is troubled by repeated, unwanted images of harming his own child, which he finds horrifying and completely contrary to how he actually feels. He recognises the thoughts as arising from his own mind, tries hard to resist them, and is acutely aware that they are excessive and irrational, which itself causes him great distress and guilt. What is this?

This is an obsession: a thought, image, or urge recognised by the person as their own, intruding against their will, accompanied by awareness that it is excessive or irrational, with content frequently opposite to what the person values, contributing to distress and guilt. It is not thought insertion, since he recognises the thought as his own, however unwelcome, rather than attributing it to an outside agency. It is not a delusion of guilt, since he is not holding a fixed false belief that he has already done wrong — he is resisting an unwanted intrusive thought while retaining insight that it is irrational. And it is not a passivity phenomenon, since there is no conviction that an outside power is controlling his actions or feelings.