Father Kevin Flannery S. J., who teaches philosophy at the Gregorian, has this to say about Cathy Kaveny's position on the Phoenix case:
--- If one follows Thomas Aquinas’s action theory—and I would argue that the Church’s action theory is Thomas’s action theory—the basic error of Kathy’s argument lies in the sentence, "The immediate aim (object) of the procedure is simply to separate the baby from its dependence on the mother’s system, not to kill the baby, either as an end in itself or as a means to another end." The object of the procedure is not the "aim" in the sense of what the agent hopes to achieve but rather the fetus’s skull (or spine or whatever). Scholars who oppose traditional Catholic teaching on cases such as the craniotomy case (and also, for instance, on the use of condoms where one spouse is HIV positive) tend to argue that the object of a human action cannot be physical object such as a skull. This goes against what Thomas says, for instance, at ST 1-2.18.2 ad 1. He also maintains that a moral object (such as a baby’s skull) is a moral object in so far as it is part of the larger structure of a human act [ST 2-2.58.3 ad 3]. These are not incompatible propositions.
In any case, it is the object of the external act that gives it its species, "what it is." What the external act is has a bearing upon the human act’s moral character: that is why Kathy does not want to say that the act is (has the species of) (e.g.) crushing a fetus’s skull. If one knows that such an act will kill the fetus, it is called ‘killing a fetus,’ i.e., killing a human being. The act performed in the Phoenix case apparently had a fetus’s skull (or some other vital part) as its object; that object makes that act to be an act about that object, not about separating the baby from its dependence on the mother’s system—or, at least, not solely about that. Anscombe would not have tolerated such selective descriptions of what one was intending. As she says in paragraph 25 of Intention: "The idea that one can determine one’s intention by making such a little speech is bosh."
I think I'd have to agree with those "scholars who oppose traditional Catholic teaching" -- the object of the act cannot be some thing, like the skull, by itself. The skull can be the matter of the object, but the object cannot be limited to it.
The (what is the word I am thinking of -- not proximate) remote end of the act may be to separate the baby from its dependence on the mother's body, but the proximate end, which is what the act achieves, is the crushing of the baby's skull, which does end the baby's life. Can one intend to crush the baby's skull without intending its death? I don't think the morality of the act can be "saved" through an attempt at double-effect reasoning.