Derek Parfit in his landmark Reasons and Persons1 asks us to imagine the following hypothetical case. You must have a very painful operation for which there is no anaesthesia. You will experience excruciating pain for several hours. But then you will be given a drug to induce amnesia. You will not remember any of the pain. You wake up in bed in hospital. Doctors come and say there has been a mistake. There are two patients due to have this procedure. They don't know if you were the patient who had this procedure done yesterday, or if you are the patient who must have this procedure today. They go away to try to find out which patient you are. Parfit claims that you have reason to hope you are the patient who had the procedure done yesterday.

While this was a hypothetical scenario written in 1984, there is a real life correlate of sorts. One problem in anaesthesia today is “awareness”. This occurs when patients partially or fully wake during an operation. Sometimes, they cannot move or speak because they have been given a neuromuscular blocker, but they can hear, think, feel, and experience pain and fear. Some patients develop post-traumatic stress disorder because of the terrifying memory of this experience. If an anaesthetist becomes aware that the patient is aware, drugs like midazolam or propofol can be given to induce amnesia of the event, as in Parfit's example.

But how bad is past pain, even if we cannot remember it? It may be better than present or future pain, but is it nonetheless bad for a person? Should patients who experience such awareness be owed compensation? Should this possibility be discussed prior to surgery and the patient asked whether they wish to be given agents to induce amnesia. …