On the face of it, the protracted public controversy over abortion in the United States and elsewhere might seem to rest on intractable normative questions inaccessible to economic analysis. But an influential early essay in the now sizable philosophical literature on the subject suggests otherwise. Judith Jarvis Thomson disarmingly inclined toward the view that “the fetus has already become a human person well before birth”,. presumably with all the rights pertaining thereto. She denied, however, that such rights necessarily include use (...) of the mother's womb until birth. To illustrate her point, she compared the mother's situation to that, for example, of an unwilling Good Samaritan with a uniquely suited blood type, who is forced to share a kidney for 9 months with a famous, ailing violinist who needed its use for that duration to recover. Even if the life of a human being was at stake, the assertion of rights for the violinist or the fetus, she argued, would be too degrading for either the Good Samaritan's or the mother's status as a person, where large unwanted sacrifices would be required. Reduced to its economic essentials, the argument is that the mother has property rights to her own body, including the right to expel a “trespasser”. who would die as a consequence. Thus, the antiabortion position is neatly undercut by granting its major premise while denying its conclusion. (shrink)