The philosophical aspects of the abortion debate are logical arguments that can be made either in support of or in opposition to abortion. The philosophical arguments in the abortion debate are deontological or rights-based. The view that all or almost all abortion should be illegal generally rests on the claims that (1) the existence and moral right to life of human beings (human organisms) begins at or near conception-fertilization; that (2) induced abortion is the deliberate and unjust killing of the embryo in violation of its right to life; and that (3) the law should prohibit unjust violations of the right to life. The view that abortion should in most or all circumstances be legal generally rests on the claims that (1) women have a right to control what happens in and to their own bodies; that (2) abortion is a just exercise of this right; and that (3) the law should not criminalize just exercises of the right to control one's own body and its life-support functions.
Although both sides are likely to see the rights-based considerations as paramount, some popular arguments appeal to consequentialist or utilitarian considerations. For example, anti-abortion groups sometimes cite alleged medical and psychological risks of abortion, such as the existence of post-abortion syndrome or the abortion–breast cancer hypothesis. On the other side, abortion-rights groups say that criminalizing abortion will lead to the deaths of many women through "back-alley abortions", that unwanted children have a negative social impact, or conversely cite the legalized abortion and crime effect, and that reproductive rights are necessary to achieve the full and equal participation of women in society and the workforce. Consequentialist arguments on both sides tend to be vigorously disputed, although they are not widely discussed in the philosophical literature.
Contemporary philosophical literature contains two kinds of arguments concerning the morality of abortion. One family of arguments relates to the moral status of the embryo—whether or not the embryo has a right to life, in other words whether the embryo is a person in a moral sense. An affirmative answer would support the (1) claim in the central anti-abortion argument, while a negative answer would support the (1) claim in the central abortion-rights argument. Another family of arguments relates to bodily rights—the question of whether the woman's bodily rights justify abortion even if the embryo has a right to life. A negative answer would support claim the (2) claim in the central anti-abortion argument, while an affirmative answer would support the (2) claim in the central abortion-rights argument.
Philosophical argumentation on the moral issue Arguments based on criteria for personhood
Since there is a continuous progression from zygote to embryo to fetus to baby, questioning the beginning of personhood could lead to an instance of the sorites paradox, also known as the paradox of the heap. Mary Anne Warren, in her article arguing for the permissibility of abortion, holds that moral opposition to abortion is based on the following argument: It is wrong to kill innocent human beings. The embryo is an innocent human being. Hence it is wrong to kill the embryo. Warren thinks that "human being" is used in different senses in (1) and (2). In (1), "human being" is used in a moral sense to mean a "person", a "full-fledged member of the moral community". In (2), "human being" means "biological human". Warrens holds that while the embryo being a biologically human organism or animal is uncontroversial, it does not follow that the embryo is a person, and it is persons that have rights, such as the right to life.. The same point is made in ; ; ; and elsewhere. "Person" can also be used in two senses. In John Locke's sense (consciousness as the basis of personal identity, which is often employed in discussions of personal identity), "person" is a descriptive term that tells us about a being's psychological properties. In Warren's sense, "person" is a moral or evaluative term that tells us about a being's moral properties. Warren and others hold, however, that being a person in the moral sense actually requires being a person in the psychological sense. To help make a distinction between "person" and "biological human", Warren observes that humans should respect the lives of highly intelligent aliens even if they are not biological humans. She thinks there is a cluster of properties that characterize persons:. and also refer to a "cluster" of properties as constituting personhood. Consciousness of objects and events external and/or internal to the being, and in particular the capacity to feel pain. Reasoning, the developed capacity to solve new and relatively complex problems. Self-motivated activity, which is relatively independent of either genetic or direct external control. The capacity to communicate, by whatever means, messages of an indefinite variety of types, that is, not just with an indefinite number of possible contents but on indefinitely many possible topics. The presence of self-concepts, and self-awareness, either individual or racial, or both. A person does not have to have each of these but if something has all five, then it definitely is a person whether it is biologically human or not, while if it has none or perhaps only one, then it is not a person, whether it is biologically human or not. The fetus has at most one, consciousness and this only after it becomes susceptible to pain—the timing of which is disputed, and hence is not a person. Other writers apply similar criteria, concluding that the embryo lacks a right to life because it lacks self-consciousness,Michael Tooley argues that the bearer of a right to life must conceive of itself "as a continuing subject of experiences and other mental states" , or must at some time possess "the concept of a continuing self or mental substance" . or rationality and self-consciousness, or "certain higher psychological capacities" including "autonomy". Others conclude that personhood should be based on the brain birth concept, which is in essence the reversal of the brain death used as a modern definition of medical death. Under this proposal, presence of brain waves would be enough to grant personhood, even with other features lacking. Based on whether brain activity in the brain stem, or just in the cerebral cortex, is relevant for personhood, two concepts of brain birth emerge, namely at the first appearance of brain waves in lower brain (brain stem), or about 6–8 weeks of gestation (paralleling "whole brain death"), and at the first appearance of brain waves in higher brain (cerebral cortex), or about 22–24 or 24–28 weeks of gestation (paralleling "higher brain death"). Different writers place brain birth at numerous points, from as early as 25–40 days to as high as 32–36 weeks, with 8 weeks and 22–24 weeks as alternatives. For other writers, the concept itself is open to question. For example, a 1989 review of previous discussions of the concept, which placed brain birth at various points between 12 days' and 20 weeks' gestation and emphasized the symmetry of brain birth and brain death, concluded that "if the concept of brain birth is a valid one, it should be placed at 24–28 weeks' gestation. More importantly, it is concluded that the differences between brain development and brain death throw doubt on the concept itself."
Although these writers disagree on precisely which features confer a right to life,On the anti-abortion side, it is similarly unclear which features one must have a natural capacity for, in order to have a right to life (cf ), or which features constitute a "future like ours". they agree those features must be certain developed psychological or physiological features which the embryo lacks. Warren's arguments face two main objections. The comatose patient objection claims that as patients in a reversible coma do not satisfy Warren's or some other criteria—they are not conscious, do not communicate, and so on—therefore they would lack a right to life on her view.; ; ; ; ; . One response is that "although the reversibly comatose lack any conscious mental states, they do retain all their unconscious [or dispositional] mental states, since the appropriate neurological configurations are preserved in the brain.", original emphasis; see ; ; . This may allow them to satisfy some of Warren's criteria. The comatose also still possess brain activity (brain waves), so this objection does not apply to brain birth theories. Finally, there are some post-natal humans who are unable to feel pain due to genetic disorders, and thus do not satisfy all of Warren's criteria. The infanticide objection argues that infants (up to about one year of age, since it is only around then that they begin to outstrip the abilities of non-human animals) have only one of Warren's characteristics—consciousness—and hence would have to be accounted non-persons on her view, and thus it is argued that her view would permit not only abortion but infanticide. Warren agrees that infants are non-persons and so killing them is not strictly murder but denies that infanticide is generally permissible. Once a human being is born, Warren argues that there is no longer a conflict between it and the woman's rights, since the human being can be given up for adoption. Killing such a human being would be wrong not because it is a person but because it would go against the desires of people willing to adopt the infant and to pay to keep the infant alive. This clarification has critics of its own, as beef cattle, chickens, or any other livestock raised for meat—or even some plants—have supporters who would pay to keep them alive. A response to these supports might be that, while livestock, plants, and infants are all not morally persons, the infant is the only life that can be designated a human being, and thus Warren's argument suggests an inherent value for the life of human beings that are not persons over lives that do not have the potential for becoming a person. Warren grants that her argument entails as a logical consequence that infanticide would be morally acceptable under some circumstances, such as those of a desert island. Philosopher Peter Singer similarly concludes that infanticide, particularly of severely disabled infants, is justifiable under certain conditions. Jeff McMahan grants that, under very limited circumstances, it may be permissible to kill one infant to save the lives of several others. Opponents may see these concessions as a reductio ad absurdum of these writers' views, while supporters may see them merely as examples of unpleasant acts being justified in unusual cases. Since brain waves appear in the lower brain (brain stem) in 6–8 weeks of gestation and in the higher brain (cerebral cortex) in 19–20 weeks of gestation, both "whole brain" and "higher brain" brain birth personhood concepts based on the presence of brain waves do not permit infanticide.
Natural capacities view