“Both a fetus and a newborn certainly are human beings and potential persons, but neither is a ‘person’ in the sense of ‘subject of a moral right to life’. We take ‘person’ to mean an individual who is capable of attributing to her own existence some (at least) basic value such that being deprived of this existence represents a loss to her.”The academic use of "her" to avoid sexism is unusually appropriate, since the majority of abortions are of female children.
The argument sounds at first blush like the kind of argument I would expect from an ethicist with proper training, because the potential/actual distinction was important to Aristotelian theories of generation. This arises from the form/matter distinction, and from Aristotle's theory of motion and change. In Physics 1, he argues that in order for change to be possible, you must have two contraries and a substratum to move between them. Thus, for something to become hot, hot must exist; and so must not-hot; and then there must be a third thing that isn't as hot as it could be, but moves towards maximal hotness. That which defines how hot it is possible to be is 'the actuality of hot.'
In the case of generation, form and matter are joined; but the child does not have the full actuality of Man or Woman. Obviously, at birth, the child still retains substantial potential, and it advances toward that potential over the course of its growth. Thus, if we define an actual person on Aristotle's terms, we could say that a child isn't an actual person until the child achieves its full growth both in frame and reason.
The ethicists, however, aren't doing anything as interesting or subtle as that; they are proposing a binary standard rather than a sliding scale of acutality,. Presumably a two-year-old would be 'an actual person' under this standard.
There are several things that I might say about this.
1) On the history of the idea: Aristotle himself viewed infanticide as undesirable except when the child was deformed, or in cases when population pressure made it necessary (both more serious considerations in the ancient world, when scarcity of food was a far more severe and immediate concern). He opposed abortion after the child had developed sensation, not reason. (Politics VII 1335b20-30, but see also History of Animals VII Part 3, which proposes based on dissection that male but not female children will have organs such as eyes -- that is, the necessary conditions for sensation -- at forty days' gestation.)
Interestingly, the 40-day standard was being enforced by the Church in Charlemagne's day: a woman who arranged the abortion of her child after it was forty days' old in the womb was subject to three years of penance, while a woman who did so earlier was subject only to a year's penance. The secular law, however, treated anyone who assisted in an abortion (as for example by providing abortifacient drinks) as a homicide. (See Pierre Riche, Daily Life in the World of Charlemagne, page 50).
That was not the case throughout the Western world, however; some followed the Aristotelian view and some other views on infanticide and abortion -- generally, after the second century AD, alternative views were much harsher.
2) On the proposed standard of the ethicists: Indeed it may not be obvious that the child has substantially more or less moral standing ten minutes before birth or ten minutes after; no more than wine in a pitcher is substantially different ten minutes before being poured into a glass than it is ten minutes after (unless, of course, it has been drunk; in that case, it has achieved its most blessed state about that time).
Some objections: before the umbilical cord is cut, the child is factually dependent on the mother for survival; afterwards, it is not. It has the capacity (but not the actuality, to stay with that distinction) of being independent long before then; but if the actuality is what counts, it does not yet have it. If independence is what counts, though, the child will still die without someone's care -- but it need not be the mother's, after that, so perhaps that is why she loses the right to dispose of the thing once it is born.
Alternatively, we might note that the experience of childbirth is a traumatic passage for everyone involved, not easily dismissed as meaningless. It may be that the act of birth is something that is important to our society as a rite of passage: and the child, having survived it, has thus passed into personhood ritually. In that case, the ethicists are barking up the wrong tree: the personhood of the child is nothing to do with the child, but with the rites of society. That would be coherent with many human cultures, in which rites of passage are just so abrubt: a child goes from a boy to a man in a day, or a week, or an instant, but the rite once complete is absolute.
3) The question of value is interesting. The child (according to them) does not itself value life; and so, if no one else values its life, its life is without value. That is a remarkably capitalist position to take on human life.
4) If we do want to return to a form/matter concept regarding the child, science has provided us with a genuine idea of what the form of a man or woman would be. It is their DNA structure, which does exactly what Form in the ancient sense is supposed to do: it organizes and structures the matter. This is a living principle, which exists from fertilization and begins to work as soon as the zygote begins to divide. Thus, we learn from scientific inquiry that there is not the movement in childhood from 'potentially Man' to 'actually Man.' Rather, the Form of each individual is unique, and it is actually possessed by -- and only by -- the child from fertilization.
If possession of an actual human Form is what distinguishes an actual human being, then the child is actually human from the first moments of its life.