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Thursday, December 16, 2010


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Of course, the fertilized egg divides shortly after conception, and is much more than one cell at implantation. This criteria thus has little practical utility for ethics given current technology, since even the stem cells derived from in vitro conceptions come from more than a single-cell human embryo.

Unlike drops of rain or the individuals in thought experiments in the personal identity literature, zygotes don't just split -- they duplicate themselves. This seems to me to be a relevant dissimilarity, and perhaps makes our intuitions about the cases a bit more muddy.

In any case, it may be that zygotes are of their own class: the sorts of things that can divide and survive, although the exact categories in which to describe this have not yet been thought of and explicated.

Further, can't we grant that the zygote doesn't itself have the potentiality to be a person, but nonetheless that the zygote has the potentiality to develop into a thing that does have the potentiality to be a person, and infer its right to life from this?


Why is the dissimilarity relevant? What exactly is duplication?

Your second point illustrates an approach that makes things too easy. Confronted with any difficulty whatosever one just announces: it's unique situation. How can Jesus be identical to the 2nd Person of the Trinity? He just is. This is the one unique case where two things can be the same even though differing property-wise.

Your third point is very interesting, but not very promising. For then one could say that an unfertilized egg, in virtue of having the pot. to be fertilized, has the right to life. That way lies disaster.

There is also the point that if the zygote ceases to exist when it splits/duplicates, as many argue, then there is nothing with the pot. to develop into something with the pot. to be a rights-possessor.

Hello Bill,

Surely you abandon P4 too quickly? You ask, How can one thing become two things? Perhaps this isn't quite the right question. Instead we could ask, How can something consisting of one part become something consisting of two parts? Or, more generally, How can something consisting of m parts become something consisting of n parts? The biological world is full of examples. An organism consisting of just m cells readily becomes an organism consisting of n cells by repeated cell division.

Hi David,

Not sure I follow you. If a water droplet splits into two droplets and you analyze this by saying that one thing retains its identity as the same thing except that after fission it has two disjoint proper parts, then what is it that makes this one thing the same thing over time?

In the case of water droplets, surely very little. But it seems to me a given that we identify certain assemblies of n cells as individual organisms that remain the same individuals when one of their cells undergoes division. What reason have we to reject this when n=1?

You say that the zygotic BV was not you giving as reason that the zygote ceased to exist though you still exist. But the infant BV and the adolescent BV have also ceased to exist. Surely by the same argument they weren't you either.

Aren't we back with Statue and Lump?


Sorry for the late comment. I only now remembered I left a comment on this thread, after having thought about the issue a bit tonight, and I was curious to see if you'd responded.

"Why is the dissimilarity relevant? What exactly is duplication?"

If I remember correctly from high school biology and BIO 100, when a cell divides, the genetic material within the cell is duplicated so that there is enough there for two cells. Then the genes collect together, the cell splits, and there are now two cells. Here is my point: it seems to me this is not just a cell splitting in half, but a cell's undergoing a complex expansion process (after all, the genetic material is duplicated only with material already present in the cell--it's not created ex nihilo). But then the case of a zygote dividing is not so much like a drop of water splitting or a person's separate brain hemispheres being placed in two bodies--it is the case of a thing simply expanding its borders, so to speak, like if I were take materials lying around my house and add to the outside of it.

What I say here seems to require that the zygote, or at least the thing that has the potential to be a person (and hence the right to life), is not identical with the one cell. I'm not sure what problems might rise because of this.

"Your second point illustrates an approach that makes things too easy. Confronted with any difficulty whatosever one just announces: it's unique situation. How can Jesus be identical to the 2nd Person of the Trinity? He just is. This is the one unique case where two things can be the same even though differing property-wise."

I have a couple of things to say to this. Surely it's not out of the question altogether to admit some sui generis phenomena in the universe. The world is not necessary restricted to that which we can neatly and tidily reduce and categorize. Plenty of philosophers have suggested some things as being sui generis, e.g. Scotus and the will as a non-natural agent. And it seems to me you would probably grant that free will, contingent self-determination, is a sui generis phenomena only found in rational beings with no non-controversial examples in nature. So why the opposition to the suggestion that there is another thing in the universe that is sui generis?

I grant my last point was not a great one.

Another thought occurs to me. You, if you are a substance dualist, cannot really hold that the zygote is a potential person. Suppose the zygote does survive division and eventually becomes a grown human body. That thing will not be person, nor will any part of it be a person, because a person is a thing that has a will, makes choices, has beliefs, etc., and no part of the body nor the entire thing has any of those features. So the Potentiality Argument against Abortion cannot be used by substance dualists, at least without some changes which will remove its immediate and simple intuitive appeal.

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