Let's say I'm a mad neuroscientist who successfully alters the structure of a person's brain so that they end up with a completely different personality and memory set. Have I killed this person? Should I be tried for murder?

Yes. Of course, I only think that because I think personal identity depends on continuity of memory and character traits, and I think memory and character traits are constituted by brain states. So, if you could somehow alter my brain enough to wipe out my memories (perhaps replacing them with some artificial set of memories) and change my character traits, you will have killed me. And if you did it knowingly and purposely, you have committed murder (i.e., the intentional killing of a person). But... 1. I'm not sure how our legal system would deal with it. I suspect there's something in our murder statutes that requires a dead body for a murder charge. We'd have to get our laws up to date with our science (and philosophy!). 2. Now, I've opened the door to some slippery slopes (or sorites arguments). How much of my identity does an evil neuroscientist have to mess up before he kills me. If he deletes 50% of my memories and changes half my character traits, has he killed me (killed half of...

In a recent response by Eddy Nahmias, he ended up talking about "the capacities [which] are the grounds for personhood". That made me think about arguments on abortion. Some pro-life people argue that the important thing is not the capacities some being HAS, but those that it can COME TO HAVE in some specified way (e.g., a "natural" way, or a way that is grounded on that being's "essence"). And that, they say, is what makes every fetus a person, and what makes a temporarily unconscious human a person. Both have to undergo some CHANGE before they can display specifically human traits that are important for personhood. Now, I don't find this argument very persuasive, but I really do not have a good answer to it. Could you tell me what is the difference (if any) between a one week human fetus and an unconscious adult that makes the latter a person, but not the former?

These are really tough and fascinating questions, both about what capacities are and what persons are. I hope other panelists might add to what little I have to say. What I will say (briefly, and without checking to see what the relevant literature has to say) is that one way to understand capacities is this: An object X has a capacity C to perform C-relevant functions or behaviors (C-stuff) if and only if X has a structural organization O such that, when X is in the appropriate circumstances, O allows X to do C-stuff. For example, I have the capacity to multiply any two numbers 1-13 because some structure in my brain allows me to get the right answer when the circumstances arise (e.g., when I'm asked to multiply 8 x 9 and I am awake and paying attention, etc.). Having a capacity to do C-stuff can be distinguished from having the potential to develop the capacity to do C-stuff. The potential might involve being in a position (both structurally and environmentally) to develop the...

Suppose a man commits murder and is then promptly involved in a car crash that leads to complete loss of all his memories prior to the car crash. The police have indisputable proof that the man did indeed commit the murder. Should they prosecute? If you conclude that they should because in some sense he's physically the same person what if a murderer somehow makes a copy of themselves and then commits suicide, should the copy be prosecuted? If you conclude that they shouldn't be prosecuted because the person after the accident is a different person from before the accident what if there's indisputable evidence that all of their memories will return in 5 years? 5 weeks? 5 days? To my mind the person after the accident is a different person from the one who committed the murder and should therefore not be prosecuted. If the memories return then they should be prosecuted but we shouldn't punish them for a crime "they" didn't commit. But I am unsure as to how much of their memories need to return before...

Wow, you have come up with a case I love to use in my philosophy of mind to connect issues of personal identity to moral responsibility and "moral luck." I have students read the Oliver Sacks' case of Donald ("Murder" in The Man Who Mistook His Wife for a Hat ). Donald took and, while high, killed his girlfriend. He had no memory of the incident (assume this is true for now) and was found not guilty by reason of (temporary) insanity. A few years later he was hit by a car and suddenly (re)remembered the gruesome murder (offering details only the killer could know). The case raises lots of questions: Is Donald on PCP (DPCP) the same person as Donald before (DBefore)? And is Donald at trial and the next few years (DTrial) the same as DPCP ? And is Donald after recovering his memories from the accident (DAfter) the same as ... and DTrial and DBefore?? And beyond these questions about personal identity, there's the question of moral luck: assuming that Donald before (DBefore) had no...