Abstract

The law tends to think that there is no difficulty about identifying humans. When someone is born, her name is entered into a statutory register. She is ‘X’ in the eyes of the law. At some point, ‘X’ will die and her name will be recorded in another register. If anyone suggested that the second X was not the same as the first, the suggestion would be met with bewilderment. During X's lifetime, the civil law assumed that the X who entered into a contract was the same person who breached it. The criminal law assumed that X, at the age of 80, was liable for criminal offences ‘she’ committed at the age of 18. This accords with the way we talk. ‘She's not herself today’, we say; or ‘When he killed his wife he wasn't in his right mind’. The intuition has high authority: ‘To thine own self be true’, urged Polonius.1 It sounds as if we believe in souls—immutable, core essences that constitute our real selves. Medicine conspires in the belief. If you become mentally ill, a psychiatrist will seek to get you back to your right mind. The Mental Capacity Act 1985 states that when a patient loses capacity the only lawful interventions will be interventions which are in that patient's best interests,2 and that in determining what those interests are the decision-maker must have …