Personhood Essentialism and the Argument from Substantial Identity
One such argument begins with a proposition which, along with others, George and Tollefsen advance in support of the conception threshold. This is personhood essentialism, or the belief that personhood is an essential property of all creatures that are persons. Personhood essentialism has been relied on extensively in antiabortion philosophy in defence of the view that all human. beings are persons from conception.
Philosophers who rely on this claim draw a distinction between ‘accidental’ and ‘essential’ characteristics of individuals. An accidental characteristic is a trait which an individual could either possess or lack whilst still being the same thing. I would still be me if I did not play the guitar but enjoyed ballroom dancing instead. Essential characteristics, on the other hand, are qualities without which an individual or object would not be the same basic thing that it is. It is an essential property of mine that I have the biological parents I actually have; I could not have had different biological parents and still be me. George and Tollefsen use a different example to illustrate the distinction.7 They claim it is an essential property of a dog,
George and Tollefsen (n 1) 58—9.
Rufus, that he belongs to the kind ‘dog’. Rufus will not cease to exist if he ceases to possess the ability to run, or loses his teeth, but he could never exist as something that is not a dog; that is an essential property of his.
‘Personhood essentialism’ states that the property of ‘being a person’ is essential, not accidental. For George and Tollefsen, this means that the same human being could not be a person at one time and not at another. This is because to lose or gain the property of personhood means becoming a different thing altogether. Nothing could lose or gain that property without simply going out of existence, just like a dog cannot cease to be a dog and persist as the same thing. Consequently, it is argued, if I am a person now, I must always have been a person from the very beginning of my existence. And since I began to exist as an individual entity at conception, I must have been a person from conception.
The argument rehearsed here by George and Tollefsen is recurrently used by defenders of the conception threshold of personhood. Sometimes termed the ‘substantial identity’ argument, it is in large part an argument about the possibility of substantial change: the possibility that an object or an individual can change in respect of a substantial—meaning, an essential—characteristic, and still remain the same basic thing. Those who, like George and Tollefsen, defend the conception threshold by appeal to the substantial identity argument hold that an individual or object cannot change substantially and continue to exist. When this premise is joined with personhood essentialism, and with the belief that ‘we’ are identical with biological organisms which began at conception, it supposedly yields the conclusion that the beginning of personhood is contemporaneous with conception. Conception is when all human beings begin to exist biologically, so if essential or ‘substantial’ change is impossible, and personhood is an essential characteristic, all adult human beings must have been persons from the very beginning of their existence.
From here, the task of conception threshold advocates seems, to them, to be fairly straightforward. All they need show is that human beings do in fact begin to exist as individually identifiable organisms at conception and their work is done. Once this is established, the argument from substantial identity demonstrates that, in George and Tollefsen’s words, all Homo sapiens ‘have always been persons, and will cease to be persons only when [they] cease to be, by dying’.8
What it means to ‘remain the same thing over time’ in the context of the substantial identity argument is not always perspicuous. In George and Tollefsen’s iteration, it seems they mean to say that a human being cannot change essentially and be numerically identical with her earlier self. An object at an earlier time is said to be numerically identical with an object at a later time if it is one and the same thing with the later object. Numerical identity can be contrasted with qualitative identity, where two objects are exactly alike in all of their properties but remain separate individual things, like two separate but exactly similar apples. The substantial identity argument starts out by presupposing that zygotes, embryos, and
fetuses (but not the sex cells which created them) are numerically identical with the mature human beings they will or might later become; they are the same individual things. I, for instance, am numerically identical with my fetus-self; it was me and I am it. It then runs from the claim that personhood is an essential property to the conclusion that zygotes, embryos, and fetuses must be persons. This is because of their numerical identity with mature human beings and because of the impossibility of substantial change. If I am identical with my fetus-self, and I am a person now, then I must have been a person as a fetus, since personhood essentialism holds that my fetus-self and I cannot be numerically identical without possessing all of the same essential properties.
The argument can be broken down as follows then:
- 1. A being cannot change substantially (or essentially) and remain the same individual thing.
- 2. Mature human beings are numerically identical with the zygotes and embryos which begat them. I was once a fetus and that fetus was me.
- 3. Personhood is an essential property of all creatures which are persons, thus,
- 4. C1: If I am a person, so was the zygote, embryo, and fetus which were identical with me, and
- 5. C2: I am a person, therefore so was the zygote, embryo, and fetus from whence I came.
We should note that nothing about the substantial identity argument and person- hood essentialism implies punctualism. That is, it does not entail that the beginning of personhood is a sharp threshold, or that conception is such a threshold. Rather, it argues that the kinds of creatures that can be persons at some point must be persons from the beginning of their existence, which, in the case of human beings, is conception. It is compatible with this argument to think that persons also fade into existence non-instantaneously, as newly conceived zygotes come into being. The significant conclusion is only that, once clearly in existence, those newly conceived zygotes must be persons since they are numerically identical with later persons and given that personhood is an essential property.
We can see from all of this that the argument will fail if any one of the following propositions is true:
- 1. Substantial change is possible.
- 2. Mature human beings are not numerically identical with the zygotes that begat them; I was never a zygote.
- 3. Personhood is not an essential property of mature human beings.
The first alternative—the possibility of substantial change—is reflected by Warren Quinn’s ‘process theory’ of the way morally considerable persons begin. This theory states that basic kinds of things such as persons could fade in and out of existence gradually. Just as we might perceive that something which is basically and essentially a house might come into existence as a house slowly during the process of construction, so Quinn suggests that the coming-to-be of things that are substantially persons may be a process during which human beings are at different times more or less complete versions of the same basic kind of thing. If, whilst going through this construction process, the thing retains its numerical identity, then substantial change will be possible. The same individual which is only a person-in-process at one stage will be a person at another. As Quinn argues, there are certain basic kinds which it only seems accurate to describe as partial instantiations of something else, like a house-under-construction. If the same human being is a person-in-process at one stage and a person at another, then it will have changed substantially whilst remaining the same thing numerically.
Alternatively, it might not be true that personhood is an essential property of all beings which are persons. This is alternative 3. Many will maintain that personhood is only an accidental property of mature human beings, similar to the ability to play a musical instrument. If this were true, it would be coherent to hold that the same human being goes through phases of being a person and not being a person throughout its existence, whilst remaining the same numerical thing. Again, the fact that quintessentially ‘person-like’ traits such as self-awareness and consciousness do come and go in human beings might only bolster the claim that person- hood is an accidental property. Quinn calls this the ‘stage theory’ of personhood. The stage theory holds that a human organism can remain the same (numerically identical) thing whilst going through distinct stages of lacking personhood and possessing it.
One question that might be asked of George and Tollefsen is whether they believe there are any qualities other than personhood that typical, mature human beings possess essentially. Could it not be an essential characteristic of someone that she is a mother, or that she is deaf? If these too are essential characteristics, they at least are clearly able to appear and disappear in the same human being. If the claim is rather that personhood is the only essential characteristic of human beings, we will require some further explanation as to why human beings can change in innumerable ways and remain the same numerical thing, yet cannot change in this one respect. What is so special about personhood that it, but absolutely nothing else about human beings, is like that?
What about the second alternative? The critic of the substantial identity argument might instead respond by just denying that mature human beings are in fact numerically identical with the embryos and fetuses that produced them, if numerical identity is taken to imply substantial identity. The later human beings, she might say, are basically different beings from the earlier life forms. Consequently, personhood could be an essential property of the mature human being without being a property of the earlier human organism. For proponents of the substantial identity argument, this response is taken as a challenge to defend the claim that fetuses are indeed identical with the mature human beings they become, although it is interesting to observe where this takes their argument.
Along with others who defend the conception threshold this way,11 George and Tollefsen believe that their task here is to refute the dualist conception of persons— the view that ‘we’ are ghostly substances inhabiting human machines—and they devote an entire chapter of their book to doing so. This is because of what they take dualism to imply about the conditions for persisting identity. If ‘we’ are basically immaterial substances, it seems that we could come and go from our human bodies and, consequently, that we are not identical with those bodies. If this were true, it would not follow from personhood essentialism that all human beings, including zygotes, are persons (or in other words, that humans are persons from the very beginning of their existence), since human beings would never be identical with person substances. Persons and the human bodies they inhabit would be two separate numerical things, not one and the same. Consequently, the ‘ghost in the machine’ might exist in the machine at one time and not another, and there is no reason to think that human organisms are persons at every stage of their existence, even if personhood essentialism is true.
Following this thinking, George and Tollefsen bring a whole selection of arguments to attack the credibility of dualism and endorse the antithetical view that we—the subjects of consciousness with which we identify ourselves—are identical with our human bodies, a view known as ‘animalism’. If we are one and the same thing as our human bodies and not immaterial substances, then we begin to exist when those bodies do, which, they argue, owing to biological continuity, is conception. And if we are essentially persons, then so were the zygotes with which we are identical.
It is in some ways strange, though, that the authors believe their argument for the conception threshold turns on the triumph of animalism over dualism. Firstly, the animalist criterion for persisting identity over time does not establish the truth of personhood essentialism, the main premise that George and Tollefsen need to be true. To claim that we are our bodies, and that the conditions for our continued existence as the same thing over time are merely biological, is to claim only that we are the same numerical things as the zygotes and embryos which begat us, not that being a person is an essential property of any personhood-possessing thing. The authors conclude their discussion of animalism by stating that it (unlike dualism) is not ‘in tension’ with the view that we are essentially persons.12 But it does not entail that view either. Animalism is also compatible with the suggestion that human  
beings acquire the property of personhood at some stage in their development. Animalism claims that the criterion for persisting identity is bodily continuity, not that personhood is an essential property. Thus, on animalism, the later human beings might still be persons even if the earlier ones are not.
In making the case for animalism, George and Tollefsen rely on an argument put forward by one of its chief proponents, Eric Olson. Olson calls it ‘the fetus problem’.  Put succinctly, the problem is that if we are not identical with our bodies (if animalism is not true), but instead with a substance or with mental states which animate that body, it follows that the fetuses we came from must go out of existence in order for us to materialize. Before the immaterial substance or mental states exist, the fetus is certainly an identifiable thing. But if the thing that it is— human material—cannot be identified with the later person, it seems that it must somehow just disappear when ‘we’ arrive on the scene. This seems to be clearly wrong. It is apparent to most people that fetuses are one and the same thing with the persons they turn into, not that the early human being simply ceases to exist when the person arrives (And where would it have gone? It certainly did not die).
But George and Tollefsen omit to mention that on Olson’s account, the ‘fetus problem’ is not taken to show that all biological human beings are persons from conception—that we were always persons. Quite the opposite. Olson thinks it plain that if the criterion of numerical identity is biological, the fetus may just come to be a person ‘the same way it may later come to be a musician or a philosopher’.!4 For Olson, the animalist view of identity solves the fetus problem by explaining that fetuses and the mature human beings they turn into are identical with one another solely in virtue of their physical continuity, even though the later organisms may be persons and the earlier organisms not. In other words, animalism is as compatible with the ‘stage theory’ of personhood as dualism.
Dualism need not, in fact, be in any tension with the view that ‘we’ are essentially persons, depending only on how the ‘we’ is defined. If the ‘we’ that is being identified here is the immaterial person substance, then it is certainly clear that this substance does not at any time lack the property of being a person. Given that it is this substance with which dualism takes me—my subject of consciousness—to be identified, and that this is a separate numerical thing from the human animal it inhabits, it follows from dualism that personhood essentialism could still be true, and that ‘we’ have always been persons. But it will not follow that all human organ- isms—separate numerical things—are persons from conception.
Next, the truth of animalism does not prove the impossibility of substantial change, another thing George and Tollefsen need to be true. If substantial change is possible, then the fetus can gradually become an essentially different kind of thing—a person, not just a human being—without going out of existence altogether and being replaced by something else, the same way that a caterpillar metamorphoses into a butterfly, a different sort of creature, whilst persisting as the same numerical thing. As H Tristram Engelhardt argued, we cannot just presuppose substantial continuity from conception to death. *5 Maybe substantial change is just part of the life cycle of human beings. The problem of how things can change whilst also remaining the same thing is a philosophical issue that naturally extends far beyond the abortion debate. George and Tollefsen clearly do not mean to deny the possibility of all change, but only of substantial change. Things, they say, cannot change in respect of their essential properties and remain the same thing, which is just the same as saying that things cannot change essentially, full stop.
But we will still require an explanation for why things can change in all sorts of respects whilst retaining their numerical identity but cannot change in other ‘essential’ respects, as well as some account of what makes a property ‘essential’ as opposed to ‘accidental’. It seems to be true both that a caterpillar does change substantially when it metamorphoses into a butterfly and that the caterpillar and butterfly are the same numerical thing, just as someone might think it seems obviously true both that the fetus and the developed human being it transforms into are one and the same thing, and that this individual undergoes a substantial change when it turns into a thinking, self-conscious being. It may be replied that it is just part and parcel of something’s being an essential property that the same being cannot possess it at one time and not at another, and that if anything is an essential property, person- hood surely is. But if a belief in essential properties commits us to accepting something that seems dubious—such as that the same individual cannot be a person at one time and not at another—we should not rule out the possibility that the belief rests on a mistake. Perhaps no essential properties of this kind really exist.
In a different vein, one might argue instead that the criterion of continuing numerical identity over time, whatever it is, is the only essential property which we possess, since that criterion is the only thing in virtue of which we remain the same individual thing over time. This, to me, just seems to follow from the nature of the inquiry into the persistence conditions for numerical identity. Another way to pose that question would be just to ask what is that one property which, so long as it persists in an individual, means that the individual remains one and the same thing over time. If George and Tollefsen are correct in supporting biological continuity as the criterion of persisting numerical identity (as I suspect they are), this would imply that our animal bodies are our only essential properties, and that our moral status as persons is, hence, a non-essential one. Only if we are numerically identical not with our human bodies but with a separate person substance, the crux of the dualist view, would it seem to follow that there can be no time in our existence that we were not persons. But even if this were true, it does not entail that all human beings are persons throughout their existence. For, once we swap the criterion of numerical identity for the one we get on the dualist picture, it is perfectly coherent to hold that we, the immaterial substance, always remain the same thing, but that not every living human body is at all times animated by an immaterial substance.
!5 H Tristram Engelhardt, Jr, ‘The Ontology ofAbortion’ (1974) [University of Chicago Press] 84 Ethics 223.
-  It is probably immaterial to the argument that the fetus’s identity with the later human-personwould be only theoretical if the fetus were fated to die before it becomes that human. For the argumentmight be read as seeking to establish that fetuses as a kind must possess the same essential propertiesas mature human beings they are able to develop into, given that all mature human beings were oncefetuses.
-  Warren Quinn, ‘Abortion: Identity and Loss’ (1984) 13 Philosophy and Public Affairs 24.
-  See also Christopher Robert Kaczor, The Ethics of Abortion: Women's Rights, Human Life, and theQuestion of Justice (Routledge 2011)102—21; Patrick Lee, Abortion and Unborn Human Life (2nd edn,Catholic University of America Press 2010) 33—45 and Baruch A Brody, Abortion and the Sanctity ofHuman Lije: A Philosophical View (MIT Press 1975) 134^44.
-  George and Tollefsen (n 1) 81.
-  Eric T Olson, ‘Was I Ever a Fetus?’ (1997) 57 Philosophy and Phenomenological Research 95.
-  ibid 106.