Here’s a philosophical problem I’ve been thinking about lately. The problem is that an ethical position I like conflicts with a metaphysical position I like. On the one hand, human infants and adults enjoy full moral status whereas animals have lower moral status. On the other hand, David Lewis’s view about the nature of persons is true (which is, in a nutshell, Four-Dimensionalism plus a Psychological Criterion of Personal Identity). I don’t know if I can hold both of these positions.
First the ethics. I think that, in typical cases, it is more objectionable to kill a human infant than it is to kill an animal, but that it is not more objectionable to kill a human adult than it is to kill an infant. That is, human adults and human infants are on a par; animals are lower. This is probably the “common sense” view, and I would justify it in the following (non-speciesist) way. The main reason it is wrong to kill any sort of creature (when it is wrong), is that it deprives the creature of something very valuable. So it is wrong (at least prima facie) to kill a dog because it deprives the dog of the life he would have enjoyed as a dog. It is wrong to kill a human infant because it deprives the infant of the life he would have enjoyed as a person. It is wrong to kill an adult human because it deprives him of the (rest of the) life he would have enjoyed as a person. Notice the last two – the infant case and the adult case – appeal to the same reason, whereas the reason in the dog case is different.
So even though, we can suppose, human infants are not persons in the psychological sense, infants enjoy the same status as human adults, who are persons in the psychological sense. This is because each has this feature: each would get to live life as a person if it were allowed to live. (The adult, of course, already is living life as a person.)
So even though, we can suppose, human infants have a psychological profile less impressive than that of a dog, infants enjoy a status greater than that of a dog due to their potential. Dogs will never be persons in the psychological sense. Infants will. So infants enjoy a higher status. Perhaps we can look at it like this: if you would become a person in the psychological sense, then you presently are a person in the normative sense. Your future psychological status boosts your present moral status.
Now the metaphysics. On the Lewisian view, persons a maximal aggregates of psychologically interconnected person stages. You are that four-dimensional spacetime worm that began when your psychology got rich enough and will end when you die. (And maybe you’re even temporally gappy: maybe you go out of existence if you go into a coma, or even each time you sleep! But don’t worry: you come back into existence when you wake up.)
Here’s the conflict. On the Lewisian view, it is not the case that you ever were an infant. Therefore, it is not the case that infants will be persons. This is because you are not psychologically interconnected enough with the infant you think you were. When you use the word ‘I’, you refer to a 4D being who began only when there was a kid who had an impressive enough psychology. For analogous reasons, you will never be a corpse (even though there may be a corpse there right after you die), and you will never be a severe Alzheimer’s patient (even if one day there is a severe Alzheimer’s patient carrying around your driver’s license).
Given the Lewisian view, I can no longer say, “killing an infant is worse than killing a dog because killing an infant deprives the infant of the future it would have enjoyed as a person, whereas killing a dog does not.” On the Lewisian view, the infant, like the dog, never will be a person. (Now, on the Lewisian metaphysics, there are objects that are now infants that will be persons – just take the fusion of you and the infant you think you were. But this doesn’t seem to confer the earlier infant stage with any moral status (as I need it to). For there is also the fusion of you and the first wheel ever invented. Certainly the first wheel doesn’t get a boost in moral status for this reason. (This example is due to Hud Hudson.))
So I no longer have a justification for my view that killing an infant is worse than killing a dog. What should be revised – my ethics or my metaphysics?