According to the conservative position (see, e.g. Brody 1982; Noonan 1983), abortion is an absolute moral wrong, and thus something which should never be permitted under any circumstances — not even in self-defence, such as cases where a continued pregnancy would almost certainly result in the mother’s death. A common concern among conservative anti-abortionists is that, if abortion is permitted, then respect for the sanctity of human life will be diminished, making it easier for human life to be taken in other circumstances. Arguments typically raised against abortion here are almost always based on the sanctity-of-life doctrine. One example of the kind of reasoning which might be employed to argue against abortion is as follows:

Or, to use another example:

Whether human beings do in fact have a natural right to life, and whether fetuses are in fact human beings, are matters of ongoing philosophical controversy.

According to the moderate position (see, e.g. Werner 1979; Bolton 1983) abortion is only a prima-facie moral wrong, and thus prohibitions against it may be overridden by stronger moral considerations. Werner (1979), for example, argues that abortion is permissible provided that it is procured during pre-sentience (i.e. before the fetus has the capacity to feel). Since a pre-sentient fetus cannot feel, it cannot be meaningfully harmed or benefited. Thus, as with other non-sentient or pre-sentient entities, it makes no sense to say a fetus has rights, much less a right to life. In the case of post-sentience, Werner argues that abortion may still be justified on carefully defined grounds, namely: self-defence (e.g. where the life or health of the mother would be at risk if the pregnancy was allowed to continue); or unavoidability (e.g. where abortion cannot be avoided, such as in the case of ectopic pregnancy or accidental injury). Abortions performed on lesser grounds are, according to Werner, unjustified. A more recent articulation of this position similarly holds that abortion is ‘seriously wrong’, except in rare instances — for example, after rape, during the first 14 days after conception when the fetus ‘is definitely not an individual’, where the woman’s life is threatened by the continuation of the pregnancy, and where the fetus has anencephaly (Marquis 2007: 137).

Bolton (1983) takes a slightly different line of reasoning. She argues that, since fetuses are not undisputed persons, they do not have the same rights not to be killed as do actual undisputed persons. Thus, in the case of life-threatening pregnancy, at least, a woman’s right to life overrides that of the fetus. Bolton also argues, controversially, that if women are not permitted to have abortions, the community might find itself deprived of the beneficial contributions that a woman freed of the burdens of child rearing would otherwise be free to make (p 335). She concedes, however, that there are also cases ‘in which others stand to benefit from the pregnant woman’s bearing a child’ (p 337), and that this too might contribute to the community’s benefit. The bottom line of Bolton’s position is that abortion is morally permitted in some situations, and might even be ‘morally required’ in others, but it is not morally permitted in some other types of situations. Either way, the facts of the matter need to be carefully assessed and analysed before an abortion decision is made.

Another moderate argument raised in defence of abortion is that a woman is under no moral obligation to bring a pregnancy to term, particularly in instances where the pregnancy has been forced upon her (as in the case of rape), or where the pregnancy has not resulted from a voluntary and informed choice (as in cases involving contraceptive failure or ignorance). In her classic and still widely cited article ‘A defence of abortion’ (reproduced in LaFollette 2007: 117–25), Judith Jarvis Thomson (1971) contends, for example, that even if it is conceded, for the sake of argument, that a fetus is a person, this still does not place an obligation on a woman to carry it to full term. This is because morality does not generally require individuals to make large sacrifices to keep another alive. Thus, if pregnancy requires a woman to make a large sacrifice — and one which she is not willing to make — it is morally permissible for her to terminate the pregnancy.