Arbitrariness of Different Kinds
As we have seen, one guiding rule in the conventional debate about the conditions of personhood is the avoidance of reductios. There are, on the whole, two different ways of dealing with reductio-type counter-arguments. The first is to amend or refine the conditions of personhood that one endorses in order to avoid the reductio. So, for instance, if a theory which grounds personhood status in conscious desires seems wrongly to exclude sleeping persons or those in reversible comas, incapable of such desires, the theory might be adjusted to locate moral standing in a more specific trait, such as the latent capacity for conscious desires or, perhaps, the past experience of conscious desires. It is important to understand that the success of this strategy of avoidance depends on the theory’s ability to explain and justify the amendment. It will not adequately answer a reductio if a discussant changes her criterion by fiat, just so as to dodge the counter-example, without being able to explain why the kernel of her argument about personhood makes the right discriminations when taken to its natural conclusions. In the example I gave, one must explain the justificatory basis of a ‘past conscious desires’ criterion of personhood.
The second strategy is to try to deny that the reductio is really a reductio by challenging the notion that the ostensibly absurd implication is really absurd. This strategy is favoured by some philosophers who, in response to the challenge that their criterion of personhood excludes young infants, respond by contesting the conventional moral standards according to which infanticide is strictly morally prohibited. Some historical cultures, they might mention, did not hold the same view about the moral status of young infants as do we. Perhaps we are simply in error in attributing full moral status to neonates. Perhaps, as Michael Tooley suggests, our absolute prohibition on infanticide is really just another kind of unsupportable social taboo. 
A related, but somewhat different, kind of objection is also ubiquitous in conventional debate about personhood. Contributors to that debate routinely demand of one another that their respective thresholds of personhood avoid arbitrariness, although the same word can, in this context, denote distinct kinds of objections.
In the first place, a personhood threshold might be decried as ‘arbitrary’ in the sense that it lacks a defensible, corresponding criterion for personhood. Take the conception threshold. Those who defend the conception threshold presumably do so because they endorse a criterion of personhood based on genetic humanity. Something is a person, on this view, if it belongs to the species Homo sapiens, which it does if it is an individual organism possessing a full set of human DNA. I am granting for the sake of argument in my discussion that all forms of human life post-conception are at least human beings in the strictly biological sense, albeit radically underdeveloped ones. But the defender of the conception threshold cannot just presuppose that all human beings are necessarily persons—that is what his argument needs to establish. If he is unable to explain the independent moral salience of human species membership, he will lay himself open to the challenge that his criterion is morally ‘arbitrary’, meaning simply that it lacks adequate justification.
Michael Tooley has argued that attributing special value to biological humanity per se is morally arbitrary in a very particular way—that is, it is speciesistl The speciesism challenge can be explained this way. Many would not consider it seriously morally wrong to abort a cat fetus. Although a human embryo is genetically human, it does not possess psychological capacities that are any more developed than that of the cat fetus; it is not more sentient or intelligent. Proponents of the speciesism challenge take psychological capacities such as these to be the morally relevant ones for personhood. It seems therefore that there is no reason to treat the human fetus as more morally considerable than the cat fetus. If one just asserts that the human fetus is owed more protection in virtue of being human, Tooley contends that this will entail ‘arbitrarily’ preferring one species over another, meaning, without reference to morally differentiating characteristics.
Tooley believes that the speciesism problem frustrates all proposed benchmarks of personhood during gestation, as well as the birth threshold. If one chose, for example, to propose viability as the threshold of personhood, the question will become why viable cat fetuses are not equally morally important, if speciesism is not silently in play. Tooley proposes instead that a human being is not a person until she is self-aware in the sense of possessing ‘a concept of oneself as a continuing subject of experiences’—a morally distinguishing feature that is not merely a matter of human species membership^2 This, he argues, is what is required before an individual is capable of having desires that could be satisfied by continued life, and hence, a strong interest in living. Since infants only begin to think and to become self aware at a few months of age, it is only around then that, on Tooley’s analysis, they acquire the fundamental right to life.
Defenders of the conception threshold in particular will push back against the ‘speciesism’ allegation by attempting to show that their preference for human species membership is not without justification. Homo sapiens are special, they often argue, in possessing the unique capacity for rationality and higher thinking, complex desires, unique forms of sociability, and so on. The fact that these capacities are typically borne out by adult human species members is, they say, a morally distinguishing characteristic of the human race. Against the speciesism challenge, they might retort that if an alien culture were discovered whose mature members also typically exemplified traits like rationality and higher thinking (like the Vulcans from Star Trek), all members of that species would also be persons from the beginning of their biological existence. It is not ‘sheer’ humanity, but the distinctive forms of human flourishing, which are the morally relevant characteristics.
But refining the criterion of personhood even further to ‘being a member of a species the adult members of which are typified by higher forms of consciousness’ (rationality, higher-level desires, etc) does not quite address the justification problem. One can just pose a further question. Why is it that merely belonging to a biological species the typical adult members of which are capable of higher forms of thinking itself suffices for personhood status?
Related to this first kind of arbitrariness problem—the problem of justifying a personhood threshold—is what Mary Anne Warren termed the ‘intrinsic properties assumption’.  As she described it, this is the assumption that only facts about the ‘intrinsic’ properties of individuals can justify ascriptions of moral standing. Conversely, properties that are only circumstantial or relational, like the property of being in a certain location, or of being wanted and loved, are irrelevant to moral standing. It is plain to see how the intrinsic properties assumption underlies many of the key moves in the traditional debate about prenatal personhood.
Characteristics like human appearance, size, and movement in the womb are often quickly dismissed as lacking intrinsic enough a quality to be meaningful for person- hood. Surely human beings do not derive their moral status from how they look, their size, or how much they can move (what about the permanently paralyzed?). It is only morally meaningful, or ‘intrinsic’, properties which matter.
The intrinsic properties assumption is an important pillar of the discussion about the birth threshold of personhood and the moral difference between late abortion and infanticide. One very familiar claim is that the mere fact of having been born cannot alter a human being’s moral status, since it is not an ‘intrinsic’ property, but only a matter of location. A thirty-week-old fetus in utero is not intrinsically different from a baby born prematurely at twenty-four weeks, or so it is claimed. How can the fact of being one side or the other of the vaginal canal make such a difference to their respective rights to life? It is in this precise way that birth is said to be an entirely ‘arbitrary’ threshold of personhood. From here it is argued that the defender of the birth threshold must, for consistency, either concede that late abortion is morally impermissible, or relax her moral opposition to infanticide.
The intrinsic properties assumption also drives objections against other thresholds of personhood that appear to depend on allegedly extrinsic factors, including the viability threshold. Whether a twenty-four-week fetus can survive outside of the womb or not, it is argued, largely depends on the standard of neonatal care in the place which it is born.  A twenty-four-week fetus inside a pregnant woman on a plane is not viable for the few hours it is in the air, but could become so again when the plane lands and neonatal care units are in close proximity. Could personhood status be as periodic as this? Similarly, ‘relational’ theories which seek to tie the acquisition of personhood to a certain kind of relation to born human beings— being wanted by them, or able to interact with them—are criticized for grounding personhood in purely ‘extrinsic’ properties.^ It seems altogether wrongheaded to argue that an unloved and unwanted newborn is, by virtue of those facts, less of a person than a cherished one, and this seems to be implied by the relational view. Equally implausible is the idea that a human being who finds himself isolated from other humans from birth, like Tarzan in the jungle, consequently lacks personhood status.
It is not always noted that we should expect the distinction between ‘intrinsic’ and ‘extrinsic’ properties to blur at some point. The capacity for rational functioning is widely regarded as an intrinsic feature of human beings, but it too may often depend on ‘extrinsic’ factors. For example, someone who suffers severe brain injury in an accident might be unable to regain rational functioning without the existence of advanced medical care, the availability of which is a matter of circumstance.
Which side of the intrinsic-extrinsic divide a property falls down on will also depend on just how one expands the definition of those terms. Viability is often considered an extrinsic property because it can depend on so much outside of the fetus itself. However, reaching a gestational age from which it can survive outside of the womb without extraordinary efforts of modern medicine might plausibly be described as an intrinsic developmental threshold, mostly having to do with lung development. As H Tristram Engelhardt noted in his discussion of the viability threshold, viability in this sense is more of a biological than a situational fact, and is far less of a moving goalpost. In fact, the lower limit of ‘biological’ viability has not been significantly affected by advances in neonatal care. It might also be wondered whether its location inside the womb could not be an ‘intrinsic’ property of a fetus, where intrinsic is taken to mean innate or non-circumstantial. The fetus could not have existed in any other situation, and its dependence on the pregnant woman’s body for survival is certainly no less a biological fact than facts about its brain development. Is enclosure within the womb a strictly extrinsic property of some human beings?
The kinds ofjudgements driven by the intrinsic properties assumption also point to a second form of potential arbitrariness in the personhood debate: that of not treating like cases alike. This is not exactly the same as arbitrariness in the sense of lacking good reason or justification for one’s proposed criterion (or criteria) of personhood, although it certainly springs from it. Part of the infanticide problem, for instance, is that the birth threshold seems to treat late fetuses differently from newborns without clear justification. The threshold thus seems to make ‘arbitrary’ differentiations between morally similar cases. It is generally seen as a failing of any account of personhood if it appears to treat creatures possessing the same intrinsic features differently. The speciesism challenge could be partly understood as an objection based on arbitrariness of this kind, since it entails the claim that various accounts of personhood fail to treat intrinsically similar creatures—cat fetuses and human fetuses; or human infants and adult chimpanzees (whose cognitive capacities may be more or less on a par)—alike.
There is a third kind of arbitrariness complaint frequently directed at attempts to locate the beginning of personhood during gestation or beyond. This is arbitrariness of the sorites kind, captured by the classic paradox of the heap. Suppose I begin to pull grains of sand together, one single grain at a time. Eventually, if I keep going, a heap of sand will materialize. I ask you to tell me at exactly which point the heap comes into existence. Which individual grain makes the difference? There you will have a bit of a problem. This is because there is no single grain about which it can plausibly be argued that its addition turned a non-heap into a heap. For whichever grain one might choose, there is nothing to distinguish it from the immediately succeeding or preceding ones. Why the one hundred-thousandth grain, and not the grain immediately before or after that? Surely the collection of sand does not become something altogether different between those individual grains.
In the debate about prenatal personhood, it seems that defenders of the conception threshold sometimes impugn post-conception benchmarks of personhood for being arbitrary in the sorites sense. That is, they take it to be a failing of developmental thresholds that they cannot be non-arbitrarily distinguished from the closest neighbouring points in the biological life of a human being.
Take the birth threshold. The challenge based on sorites arbitrariness will ask how the moment of birth can be distinguished from the moments immediately preceding it, when the fetus passes down the vaginal canal. As Christopher Kaczor asks: ‘is there really any important difference in the personhood of a human being one minute before birth and one minute after?’ But it is equally as impossible to non-arbitrarily distinguish the few moments before birth from the moments immediately preceding them. So things get even worse for developmental thresholds, or so the argument goes. Whichever development is settled upon as the critical bench- mark—be it birth, viability, sentience, or consciousness—will ultimately equate personhood’s beginning with a threshold that is not morally distinguishable from the developments occurring just moments before, and the same will continue to be true however far back one moves the threshold. This is owed to the incremental nature of all human development before birth, and indeed, after it. Kaczor sums up the apparent problem this way:
The conception of personhood used by defenders of infanticide also leads them to posit arbitrary deadlines to separate who may live from who may be killed. Indeed, setting the age for voting or driving is indeed arbitrary ... However, in matters of life and death we must do better than picking a random cut-off point. Life itself is at stake, the existence of innocent human beings, and so a vision of personhood that rests on the arbitrary decisions of the powerful against the weak cannot be in conformity with the demands of justice or equality.18
The claim that developmental criteria for personhood cannot be reconciled with basic human equality is an independent problem that I will consider in chapter 8. The claim I am interested in here holds that the correct threshold of personhood must not be arbitrary in the sorites sense (we can say: must not be sorites-susceptible). It is a problem of cut-offpoints.
For Kaczor and other critics of developmental thresholds, the fact that those thresholds do not pick out a precise, non-arbitrary cut-off point is a fundamental flaw, and attests to their falsity. In particular, it is often argued that where a posited threshold of personhood is sorites-susceptible, no reason exists to refrain from pushing it further and further forward. If twenty-four weeks’ gestation, why not twenty-five? If birth, why not a few hours after? If two weeks of infancy, why not a month? The result, it is argued, is a disconcerting slippery slope, which threatens to rationalize a later and later threshold of personhood.
18 ibid 36.
As Kaczor acknowledges, sorites arbitrariness rears its head in all kinds of other contexts too. When we set the voting age at sixteen, or the driving age at seventeen, we cannot explain why a teenager a day before her sixteenth or seventeenth birthday is less capable of voting or driving competently than she is the day after. But this does not render the threshold unreasonable. In many contexts, then, sorites arbitrariness simply does not worry us, and does not logically entail any kind of slippery slope. Those who, like Kaczor, believe that it is uniquely problematic in a proposed threshold of personhood will therefore need to explain why.
Along these lines, it seems that the question about the threshold of personhood will need to be distinguished from the paradox of the heap itself. In the sorites paradox, we know that the grains of sand become a heap at some point, even though we cannot pinpoint any non-arbitrary moment when this occurs. The reasonable conclusion, in the heap case, is not to say that the heap exists with the first grain of sand, just as the reasonable response to sorites arbitrariness surrounding our driving age limit is not to allow babies to drive. These are clearly absurd reactions to sorites arbitrariness. Again, then, a defender of the conception threshold who believes that the continuous nature of human development helps her case will have to explain why the sorites-susceptibility of any developmental threshold of personhood has such a radically different implication, compelling us to identify personhood at the very beginning of biological human life.
As I said, the three kinds of arbitrariness I have outlined are not entirely distinct from one another, but are in significant ways related and mutually reinforcing. If a threshold is revealed to be arbitrary in one sense, it could quite possibly, and for the same reasons, be described as arbitrary in one of the other two senses as well. But all three capture standards of correctness that are accepted by many discussants in the personhood debate and used as grounds for criticism of competitor thresholds. Here, I wish to focus special attention on arbitrariness in the third, sorites sense. In particular, I wish to consider what deeper commitments about the nature of per- sonhood one might need to embrace before imperviousness to sorites arbitrariness can be set up as a standard of correctness that a threshold of personhood needs to surmount. What kind of property must one take personhood to be for such a standard to apply? And which personhood threshold could possibly meet it? Subjecting these underlying commitments to scrutiny will, I think, reveal something about how it is reasonable to think that persons begin.
-  Michael Tooley, ‘Abortion and Infanticide’ (1972) 2 Philosophy and Public Affairs 37.
-  ibid.
-  ibid 9.
-  Mary Anne Warren, ‘The Moral Significance of Birth’ (1989) 4 Hypatia 46, 47—8.
-  Kaczor (n 4) 68-71.
-  For an example, see Jonathan Herring, ‘The Loneliness of Status: The Moral and Legal Significanceof Birth’ in Fatemah Ebtehaj and others (eds), Birth Rites and Rights (Hart Publishing 2011).
-  H Tristram Engelhardt, Jr, ‘The Ontology of Abortion’ (1974) [University of Chicago Press] 84Ethics 217, 228—30. In 2007, after reviewing all the evidence on fetal viability, the House of CommonsScience and Technology Committee concluded that while survival rates of twenty-four weeks’ gestation and beyond had improved in recent years, there was no evidence to suggest that fetal viabilityhad been significantly lowered since the upper time limit for abortion had last been set (House ofCommons Science and Technology Committee, ‘Scientific Developments Relating to the AbortionAct 1967’ http://www.publications.parliament.uk/pa/cm200607/cmselect/cmsctech/1045/ 1045i.pdf,13—15 (last accessed 11 October 2016)).
-  Kaczor (n 4) 49.