Wesley Clark takes conventionalism about personal identity to the extreme. Many philosophers think what makes someone a person are complex social practices, including language use and moral views. If we used language diferently and had different moral views, we would have a different concept of personhood, and the word 'person' would mean something different.
A new kind of conventionalism has been endorsed by General Wesley Clark. Most philosophers in the abortion debate realize that the debate is about personhood and not life, since life certainly begins at conception, as anyone with a basic Biology 101 class should know. So I'm going to assume that Clark means personhood and not life. If he really means life, he's more of an idiot than I thought.
Anyway, Clark said, "Life begins with the mother�s decision." If he's right, then whether a fetus is a person depends not on anything scientifically or philosophically discoverable. It depends merely on the decision of the mother. This is a kind of conventionalism but an extreme one. The only convention that matters is that of one person. How can one person's choice make the difference between whether something is a person? (You can see how it would be worse if her choice determined even if it was alive.)
Now there's a view in philosophy called divine voluntarism, basically that God's choice determines something. You could be a voluntarist about morality (Ockham's view that God determines what's right and wrong) or about mathematical truths (Descartes' view that God decides whether 2+2 is 4 or 5). You could be a divine voluntarist about persistence through time (Jonathan Edwards' view that God decides whether something is the same thing as some earlier thing). Professor Jose Benardete at Syracuse University, where I'm working on my Ph.D., was at one point (unsuccessfully) trying to convince Dean Zimmerman (once at Syracuse but now at Rutgers) to argue for divine voluntarism about where the line between bald things and non-bald things occurs (in terms of number of hairs, location of hairline, etc.).
Voluntarism makes sense for some human decisions. If we need a name to call something, it's perfectly appropriate to stipulate that we name it after the person who discovered it. Human choice then determines what sound we will use to refer to that newly discovered thing. We have a congressional voluntarism (or a sort) about laws. It makes absolutely no sense for some person to have the ability to determine, all by her lonesome, whether something is a person. This position will henceforth be known as maternal voluntarism about personhood (or maternal voluntarism about life, if you prefer to discuss the absolutely moronic view that he literally espoused, but I'm trying to assume that he only meant the relatively moronic view that I've been discussing).
See other good criticism at Outside the Beltway, Matthew Stinson, and Balloon Juice. Apparently his view is far more extreme than Roe v. Wade, which allows states to restrict abortion after viability (which at the time was 25 weeks but now has moved to 20-21 weeks). Clark doesn't think the government should restrict abortion until birth, which presumably would allow an abortion during active labor. So it's legal for a state to prohibit abortion in the second half of pregnancy, but Clark wouldn't appoint a judge who agreed with that. So he inconsistently says both that he couldn't appoint a pro-life judge, because a pro-life judge is somehow incapable of rendering a decision consistent with precedent, while also saying something himself that's inconsistent with precedent -- that abortion shouldn't be restricted at all, even up to the moment of birth. So much for following precedent.