Arguing with abortion opponents at other blogs lately, I've seen the following argument numerous times:
- Any line we draw distinguishing the definitely-alive newborn baby and the questionably-alive freshly fertilized human egg is going to be artificial.
- Hence, there is no real distinction between a newborn baby and a freshly human egg.
- Hence, we have the same duties to both a newborn baby and a freshly fertilized human egg.
- So abortion cannot be distinguished from infanticide; and since the latter is clearly wrong, the former must be as well.
How is the inference from (1) to (2) supposed to go? There seems to be an assumption here, that real distinctions require sharply-drawn categories. But Aristotle's case study provides us with an excellent counterexample: the distinction between musical and unmusical is certainly a real distinction, but there is no moment at which the change actually takes place. This change actually parallels pregnancy quite well: we start with some things that clearly don't amount to a new person (a sperm and an egg), and nine months later end up with something that clearly is a new person (a newborn baby); and we needn't point to one single instant where personhood suddenly appears on the scene to recognize the reality of the change over time.
Going further, I would argue that personhood (and here I mean rational agency) and life, like musicality, are not metaphysically simple, and hence all three can serve as paridigm cases of gradual change with a fuzzy period of transition. For life, consider suspended animation: the yeast at the supermarket, for example, is not metabolising, but nor is it dead; it's in the transition phase between the two, and giving it warm water and food will bring it back fully. For rational agency, consider a dog. My mom's dog, Buddy, in particular. Buddy is smart enough to figure out how to unlock gates, unless they're secured using a lock that needs an opposable thumb to open; but at the same time, he clearly doesn't use language or undertake long-term projects or engage in any other sort of abstract thought. I think one could argue that a dog has a certain amount of rational agency -- he's able to choose to undertake projects to achieve his desires -- but not as much as a human or other ape -- we can use language and reason abstractly.