Judith Thomson argues that a fetus may have a right to life yet lack the right to use its mother's body to stay alive. According to Kenneth Einar Himma, Thomson's argument applies only to cases where the parties meet two conditions. First, they must “have a history of physical independence” and, second, they must be “autonomous moral agents, capable of incurring obligations.” Himma devises a case involving conjoined twins to show why the mother–fetus case does not meet these conditions.