What it is to be a person is a principal topic of metaphysics. Ideally, a pure metaphysical theory expresses a moral detached interest in how to distinguish persons from nonpersons. However, the metaphysics of persons has often been put to work to defend a preferred moral outcome, placing metaphysics in the service of ethics. Metaphysics is invoked to inquire whether individuals have rights and whether the theory of persons can address practical problems of abortion, reproductive technology, infanticide, refusal of treatment, senile dementia, euthanasia, the definition of death, and experimentation upon animals.