In a recent book, I attempt to use the metaphysics of Thomas Aquinas to defend a moderate view regarding abortion: that an abortion at any time during a pregnancy should be considered a grave loss, but that it should be considered murder only after roughly the middle of the second trimester. John Haldane and Patrick Lee contend that I have misunderstood the implications of Aquinas's view, and that in fact his metaphysics supports the conclusion that a human being comes into existence at the moment of conception. In this paper, I make a brief reply.