If viruses are not life forms, should abortion always be permitted?

Terminating pregnancies can be considered objectionable on a range of grounds. The unborn have rights, women have duties to their families and communities, the wealth of nations depends on new producers, consumers, and soldiers, and so on (Häyry, 2023). We concentrate on a very specific corner of this wide issue.

One argument in the abortion debate states that the continuation and termination of pregnancies should be a matter for the pregnant women to decide, because their right to control their own bodies is, or should be, undisputed (Stevenson, 2019). “My life, my body, my choice”.

We sidestep the normative claim about personal sovereignty and focus on the factual dimension of life. Our inquiry, inadvertently prompted by Rosalind Hursthouse's (1987) rejection of metaphysics from the abortion debate, challenges standard views on life in this debate and comes to a striking conclusion. If viruses are not life forms, and if we assume an updated Aristotelian take on life, fetuses are not life forms, or life, either, and a popular argument against abortion rights evaporates.

In what follows, we proceed in four stages. We first locate our target argument in the abortion debate and outline Hursthouse's approach to the matter it raises. We then move on to analyze what life means in the context of viruses, fetuses, and Aristotelian metaphysics. In the light of this knowledge, we identify three possible routes to proceed in an Aristotelian spirit. In the fourth and final section, we formulate a defense for our claim by an appeal to the parasitic nature of viruses and fetuses; and conclude our demonstration by pointing out the limitations of our case.

The argument that, according to our claim, evaporates is, in fact, a counterargument to a popular defence of the right to choose abortion. The discussion is historically layered but a relatively noncontroversial description of modern developments begins with this syllogism – P stands for “premise”, C for “conclusion”:

• P1 Killing beings who have a right to life is not permissible.

• P2 Abortion kills beings who have a right to life.

• C1 Abortion is not permissible.

Two objections have been raised against this deduction. Philosophers with utilitarian leanings have tended to challenge P2 by pointing out that fetuses, especially early on during the pregnancies, are not yet beings who have a right to life. That right, according to them, belongs only to more developed human beings, those who, for instance, are aware of themselves as continuous subjects of mental states such as beliefs, hopes, fears, and expectations (Singer, 1979; Harris, 1985). Philosophers with more straightforwardly liberal ideals have questioned P1 by arguing that killing beings who have a right to life may, after all, be permissible under specific circumstances. Judith Jarvis Thomson (1971) presented the seminal case of the ailing violinist to argue that pregnant women should be allowed to rid themselves of fetuses just like a kidnapped lifesaver is allowed to disconnect from the violinist.

Following Thomson's lead, the argument from women's sovereignty over their lives and bodies can be presented in the following form: ⁽¹⁾

• P3 I have a right to decide about my own life.

• P4 By deciding to have an abortion I decide about my own life.

• C2 I have a right to decide to have an abortion.

Opponents of this reasoning can doubt the validity of either premise. According to some conservative and sexist views, P3, while true for reasonable human beings, cannot be applied to women, either due to natural akrasia (Okin, 1979; Hursthouse, 1987, p. 236; Mulgan, 1994) or because pregnancy reduces an individual's mental powers (Jackson, 1984; Cohen, 2014). According to some equally conservative but not explicitly sexist views, the decision to abort does not concern just one life (Finnis, 1973; Marquis, 1989). The fetus also counts, P4 is untrue, and C2 does not follow.

The latter move runs the risk of taking the discussion back to P2 – the moral status of the unborn. What does it mean to say that the fetus also counts? Is it a moral agent or a person with self-awareness? Obviously not. Is it a potential person with the capacity to develop self-awareness and agency in the proper conditions? Obviously yes, with a convenient definition, but what relevance does this have in moral terms (Noonan, 1970; Tooley, 1972)? Is it a sentient being, capable of experiencing pain? From some point forward, yes, but again, what is the relevance (Cohen & Sayeed, 2011; Steinbock, 2011)? Or is it enough that it is alive, a life form, a life, like our wording of the argument suggests?

Rosalind Hursthouse, in Beginning Lives, famously sought to steer clear of these metaphysical disputes about the nature and status of individual fetuses, as well as of questions concerning the rightness or wrongness of particular acts or choices related to abortion (1987, pp. 89–130). Instead, she aimed to shift the discussion to what a virtuous person would think, feel, and do when faced with pregnancy and the possibility of terminating it (1987, pp. 331–339). Her view was that bearing children is an intrinsically worthwhile practice for the female of the species (1987, pp. 295–307), a consideration that tends to tip the “average woman's” balance towards carrying a pregnancy to term (1987, pp. 307–318). Her conclusion, then, was that a woman who has had children can look back at her life thinking that she has done something worthwhile, whereas “anyone who has not borne children well might have to say, ‘I haven't done anything with my life really’” (1987, p. 318).

Hursthouse's view is Aristotelian – more specifically, Neo-Aristotelian in the Thomistic virtue-ethical tradition pioneered by Elizabeth Anscombe (1957) and Philippa Foot (1978). In the context of life and abortion, this gives rise to an interesting tension. As Candace Vogler has pointed out, although “a clever philosopher can make a lot of headway in neo-Aristotelian practical philosophy without relying upon sacred doctrine”, the moral absolutes in the work of the best natural-law theorists seem to require the support of “sacred doctrine, not just a general account of practical reason” (Vogler, 2012, pp. 893, 905). Does Hursthouse, then, also need religious teaching to underwrite her “average woman” theory? She explicitly denies this (1987, p. 3), and insofar as she avoids stating moral absolutes, perhaps not. But would her view then lose some or all of its normative force? And could firmer grounds be found deeper within the Aristotelian doctrine itself – perhaps in his metaphysics of life and living beings as substances? This is the starting point of the comparison between viruses and embryos that we conditionally suggest.

Viruses are an interesting borderline case in the demarcation between living and non-living beings. They do exhibit some, but not all, of the characteristics typically associated with life. A virus contains genetic material, it can mutate and evolve, and it can reproduce albeit only within a suitable host. It does not, however, have independent metabolism, cellular structure, or capacity for self-sustaining activity. In isolation, a virus is an organized yet chemically inert macromolecule rather than an organism.

The editors of Encyclopedia Britannica (2025) summarize the current scientific understanding in no uncertain terms:

Viruses are not considered living organisms in the traditional sense. Viruses are unique infectious agents that can only multiply within the living cells of animals, plants, or bacteria. They are not free-living entities and are completely dependent on a host cell for their metabolism and reproduction. This dependency on a host for replication and metabolic functions is a key reason why viruses are not classified as living organisms.

After detailing the biology and chemistry of the case, the editors conclude that “viruses are parasites […] relying entirely on their [hosts] for [their lifelike] functions [and this] supports the classification of viruses as nonliving entities”.

On a more cautionary note, whether entities like viruses count as life depends on the definition. Some main characteristics to be considered are biochemical autonomy, evolutionary participation, and teleological organization. The aspect of dependence can be interpreted as a sign of non-life or as a mark of extreme parasitism. Conceptually speaking, the exclusion of viruses from the domain of life risks the omission of other borderline organisms such as prions and viroids, too, while their inclusion threatens to dissolve the notion of life into mere replication and information transfer.

Fetuses, obviously, are in a different category. That they are, in some sense, alive has seldom, if ever, been questioned. The genetic constituents of development are present from the moment of conception, as the slightly inaccurate – conception is a process and has no precise moment – saying goes. What has been questioned, however, is the kind of living that should count in moral considerations. Thomasine Kushner, defending the notion of “brain life”, drew the distinction between zoe, being alive, and bios, having a life, and argued that this is crucial in making normative judgments concerning abortion:

It is that only a functioning brain makes the consciousness possible on which bios depends. It is not “human life” per se that matters morally, for […] our obligations are not to protect living things but rather to protect things that have lives. From the moment of conception the embryo is alive (zoe) as well as irrefutably human; but the status of a living human being, at any stage, is not the same as that of being the subject of a life in the sense of bios. The morally significant question becomes “Is the fetus the subject of a life?”

This wording goes beyond the debate of agency and personhood rejected by Hursthouse and makes the precise nature of embryonic life focal. The metaphysical standing of entities returns, in a way reminiscent of Aristotle's observations on the matter.

For Aristotle, ⁽²⁾ a living being is a substance (ousia) with a form or soul (psyche) – the principle of life, self-movement, and organization (Bolton, 1978, p. 260). Addressing human embryos and fetuses, Aristotle distinguishes between developmental stages. ⁽³⁾ The emerging human entity first only has a vegetative or nutritive soul – it grows and nourishes itself. It then gains a sensitive or animal soul – it develops perception and movement. Finally, a rational soul appears – not generated by the parents but infused from outside (exôthen). The last stage marks the formation of the human individual as a substance, a living being.

Being a substance, for Aristotle, means to have one's form actualized, and a human is actualized in ensoulment. Before this, the embryo or fetus is a part of the pregnant woman's substance, like an organ. It is not a self-standing ousia. In ensoulment, the unborn human gains the status of a distinct living substance in its own right. In its soul, it now has an internal organizing principle. The transition, according to Aristotle, occurs some time after conception. He went on to argue that this happens at around 40 days for males, 90 for females. As Aristotle's biology is unapologetically hierarchical and sexist – the male is the paradigm of full actuality, the female, “as it were, a mutilated male” – the longer formation time for female embryos reflects, not more thorough maturation or ripening for perfection, but a sluggish developmental process due to metaphysical coldness and lack of vital heat. ⁽⁴⁾

Terminology aside, Kushner's division into humans alive and humans having a life, or being subjects of life, reflects the core of the original Aristotelian position. The dates of ensoulment in Aristotle, based on a mix of Hippocratic teaching, observation, folklore, and mythic pattern-seeking, have limited validity. Chickens were Aristotle's main embryological model. He studied eggs and registered the appearance of the heart, the growth of veins and other organs, and the movement of the chick inside the egg. ⁽⁵⁾ This is where he gets his notion that the soul appears gradually – and this, of course, makes perfect sense. The newly fertilized egg is a very different entity from an adult human being. It is just that the timing of the crucial ensoulment and its justification has been a topic of intense debate for quite some time. Hursthouse's avoidance of metaphysics stems from this. Keeping in mind her reluctance to engage in explicitly religious considerations yet recognition of them, three approaches to ethics become available in the wake of her philosophy of abortion.

The alternatives open to an Aristotelian after Hursthouse's intervention are conservative as understood by Hursthouse, theistic as explicated by Thomas Aquinas, and metaphysical as defined by Aristotle.

Hursthouse's own approach is traditionally conservative and can be encapsulated in the words quoted above – an average woman who has not borne children might have to conclude that she has not done anything, or anything worthwhile, with her life (1987, p. 318). Set in the context of abortion, this means that a woman choosing to terminate her pregnancy is in danger of sentencing herself to a meaningless life. This may be her last chance of having a child, and she may not be in a position to do other things that would be equally valuable. A non-average woman may, of course, have better opportunities in store, and even an average one can correctly assess that it would be wiser for her to postpone having children – but these are not considerations that Hursthouse would dwell in. ⁽⁶⁾

The “average woman” model can be criticized from several angles. It rests on an archaic view on gender roles and makes ungrounded assumptions about the significance of having children. Presented as an undisputed fact, and unsupported by empirical evidence, the idea reflects Hursthouse's hopes and fears more than attitudes in egalitarian democracies. Bluntly put, if a woman's worth depends on her bearing children, then the natural conclusion is that society has failed her.

Hursthouse's view finds some support in conventionally geared feminism. In the nineteenth century, Catherine Beecher and Harriet Stowe (1869) held that women are the moral backbone of societies, managing households and safeguarding the virtues of their family members. Bearing children would, of course, be a natural and commendable part of such lives. During the same era, however, different voices were also heard. Harriet Taylor Mill and John Stuart Mill (1869) argued that women are in many fields as capable as men and should be given an equal chance to forgo domestic life and seek other occupations. These, then, could have given their lives the meaning sought by Hursthouse.

Other criticisms against the “average woman” model could be raised from the viewpoint of intersectional feminism, as defined by Kimberlé Crenshaw (1989). Women of difference may face overlapping challenges which make bearing children an unachievable or unattractive option. Hursthouse's stereotype can then be both inaccurate and insulting.

The philosophy of Thomas Aquinas provides a natural Aristotelian alternative to Hursthouse's non-metaphysical approach. Instead of trusting ordinary women to identify what is worthwhile in their lives, the proper subject of virtue can be sought theoretically. Aquinas did and ended up arguing that a righteous moral character eventually needs divine backing.

One of Aquinas's favored ideas in Aristotle's ethics was “that virtue must be in a power as in a subject” (Pakaluk, 2013, p. 50) – or, as Aquinas put it in answering Question 56 of Summa Theologica, “a power of the soul is […] the subject of virtue”. ⁽⁷⁾ Aquinas then went on to identify which power of the soul is the ultimate subject of virtue. After dismissing intellect, ⁽⁸⁾ irascible and concupiscible power, ⁽⁹⁾ sensitive powers of apprehension, ⁽¹⁰⁾ and the will, ⁽¹¹⁾ he seems to conclude that the subject of moral or theological virtue, while in a human being's essence, must also, when it directs agents' affections to God or their neighbors, transcend any individual inclinations, ideas, or will and to conform with the good of humankind or Divine good – “as charity, justice, and such like”. ⁽¹²⁾

Applied to the abortion case, this means that, to behave virtuously, the average woman should, in Neo-Aristotelian parlance, understand the requirements of practical wisdom or reasonableness (Finnis, 1998; Vogler, 2012, p. 894). Regarding human life, born or unborn, these requirements are clear. The intentional taking of a human life is without a doubt morally wrong, should arguably be regarded as murder, and is a very strong candidate for an absolute prohibition (Finnis, 2021; Vogler, 2012, p. 896).

Identifying abortion as taking a human life moves the discussion to the other thread of consideration eluded by Hursthouse in Beginning Lives. Religious authority and the metaphysical status of fetuses were both sidestepped by her “average woman” approach. The way Aquinas has been interpreted in modern Thomism seems to combine these. The morally and theologically virtuous person understands that abortion is categorically forbidden because it kills the fetus. But a being can only be killed if it has a life.

Going back to the roots of this kind of thinking, Aristotle argued that fetuses become substances, living beings, when they are actualized with the appearance of their form or soul. For him, abortion before ensoulment would not have been an issue. In current medical terms, his view would sanction contraceptive pills, intrauterine devices, morning-after pills, and terminations of pregnancy up to 5–6 weeks if the fetus is male and 12–13 weeks if it is female. Only after these timelines could the charges of murder be brought to the table. Insofar as it was Hursthouse's aim to condemn also earlier abortions, she made a wise choice in avoiding metaphysics, including Aristotle's take on it.

A detail that has gone largely unnoticed in the abortion debate is that one of Aristotle's main sources of empirical observation was the egg. Questions arise here. As an egg developing into a chick forms veins and organs, we may be able to trace the emergence of its vegetative and sensitive souls. Such observations, however, do not seem to extend to a rational soul, the mark of substance in human beings. Aristotle says that if an eye were a substance, its function would be seeing. ⁽¹³⁾ Similarly, if a human being is a rational substance, its function would seem to be thinking, or at least consciousness (Kushner, 1984, p. 6).

That rational souls are undetectable in the species Aristotle studied is one problem. Another is that the eggs he observed were independent of the hens that laid them, already living their own lives. This, of course, is not the case with human fetuses: they exist within women's bodies, leading dependent lives. Any ovoid evidence Aristotle presented is, therefore, inadmissible in the case of abortion. And this is where we return to the question of the life – or non-life – of viruses.

Aristotle was not entirely amiss in his biology of becoming: fetuses do acquire characteristics and capacities as they develop. Yet they never become visibly ensouled at any stage of their growth, nor do female and male fetuses differ in accordance with any metaphysical temperature or degree of vital heat. An update is clearly needed for determining their status as living beings – and here, viruses, as a borderline case, offer a useful point of comparison.

Modern science, of course, has replaced Aristotle's notion of the soul with functional and systemic accounts of life. If we define life not merely as a biological process but as a self-sustaining, self-directing organism, then the distinction between what counts as a life form and what does not must hinge on whether the entity possesses autoteleonomy: the capacity to maintain itself, pursue its own metabolic ends, and regulate its processes independently. Under this definition, viruses are often excluded from the category of living beings because they lack autonomous self-maintenance; they reproduce only by exploiting the machinery of a host organism. They are therefore frequently described as parasitic replicators rather than organisms in their own right.

However, if one accepts this criterion for viruses, one must apply it consistently. Fetuses in early and mid-stage gestation, like viruses, lack autoteleonomy. They do not metabolize independently, regulate their internal environment, or sustain themselves without continual support from the pregnant body. All their oxygen, nutrients, waste filtration, temperature regulation, and endocrine environment are externally supplied. The placenta functions as a life-support interface; the fetus does not yet possess independent agency in any metabolic sense.

On these grounds, the fetus is not meaningfully distinguishable from a parasite in the biological sense of that term: an entity that draws resources and structural support from a host organism because it cannot survive through internal regulation alone. Indeed, in strictly biological terms, the fetus meets the definition of an obligate parasite throughout gestation. To grant the fetus the status of a “life form” while denying it to viruses – when both are dependent parasitic systems – is therefore inconsistent.

If the criterion for life is dependency, then the fetus is no more a life form than the virus. If the virus is excluded because it cannot maintain itself independently, then the fetus must likewise be excluded. The moral, emotional, or social value that societies often attach to pregnancy does not alter the biological classification under this argument. One may wish to treat the fetus as a life form for symbolic or ethical reasons, but if the classification rests on self-sustaining biological autonomy, the fetus lacks that capacity, and, by parity of reasoning, should not be considered a life form.

Our premises for reaching this conclusion have been non-conservative, non-religious, and scientifically Aristotelian. Those holding conservative, theistic, or traditional Neo-Aristotelian views will, understandably, disagree – and the points of disagreement have been clearly signposted throughout our argument.

With these qualifications, the claim stands: if viruses are excluded from the category of life on the grounds of parasitic dependence, consistency requires that fetuses be excluded on the same basis. By Aristotle's lights, the fetus becomes a substance only when it has its own principle of motion; by Hursthouse's, virtue begins in recognizing the facts of life as they are. Between the two, there seems to be no other life in there.

We must conclude with a caveat. Our conceptual argument for the comparative non-vitality of human fetuses rests on a specific kind of dependency. Even after birth, many people are particularly dependent on the assistance and services of others. Yet, without question, they have lives that are as worth protecting as anyone else's with less visible reliance on external support.

There is a difference between this kind of need and the inexorable relationship of the fetus with the maternal organism. The very young, the frail, and the very old can be sustained by a community, in other words, by any individual or group assigned to the role. They do not depend on anybody else's particular metabolism. Fetuses do, and, if our argument is accepted, this is what makes the analogy with viruses hold.