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One into two will not go: conceptualising conjoined twins
  1. M Q Bratton1,
  2. S B Chetwynd2
  1. 1The Chaplaincy, University of Warwick, Coventry, UK
  2. 2Department of Philosophy, University of Warwick, Coventry, and School of English and Philosophy, Keele University, Staffs, ST5 5BG, UK
  1. Correspondence to:
 Revd M Q Bratton
 The Chaplaincy, University of Warwick, Coventry, CV4 7AL, UK;


This paper is written in response to controversial judicial decisions following separation surgery on conjoined twins “Jodie” and “Mary”. The courts, it is argued, seem to have conceptualised the twins as “entangled singletons” requiring medical intervention to render them physically separate and thus “as they were meant to be”, notwithstanding the death of the weaker twin, “Mary”. In contrast, we argue that certain notions, philosophical and biological, of what human beings are intended to be, are problematic. We consider three compelling conceptualisations of conjoined twins and advocate a model that conceives them as two psychologically separate individuals who happen to share a body, the sharing of a body being integral to the individuality of each twin. While we reject an “essentialist” view of the conjoined state, a view which might render separation surgery unthinkable in all cases, we nevertheless argue against an “adversarial” interpretation of conjoined twins’ respective best interests. We maintain that the physical entanglement should be regarded as a shared problem rather than one posed by one twin to the other. And if, after deliberation, separation surgery is deemed the “least detrimental alternative” or the “lesser of two evils”, then there should be recognition of what conjoined twins will lose, as well as gain, through separation. The current drive to separate twins at all costs may evince a deeper unease with bodily configurations that appear to threaten the premium that the Western ethical and legal tradition places on personal sovereignty, and the physical circumscription that such sovereignty assumes.

  • body
  • conjoined twins
  • defect
  • individuality
  • person

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This article has been prompted by our deep sense of unease with the reasoning of the Court of Appeal in a case involving conjoined twins, known for legal purposes as “Jodie” and “Mary”.1 We think it is a startling example of the strong emphasis in the Western ethical and legal tradition on physical separateness as a constitutive feature of individual identity. It is also, we think, an unusually clear expression of the drive within the law, the medical profession, and the public to “customise” human anatomy in accordance with norms that associate individuality with the “standard”—that is, the physically separate, body. With advances in medical technology, a technological imperative seems to have arisen to “sculpt” conjoined twins in order to make them conform to notions of the standard body. This is so even if such reconfigurations of the human body would result in catastrophic damage to the mobility, reproductive, and life functioning of the people concerned. We believe that this imperative derives, in part, from the desire to make the anatomically abnormal conform to what makes us feel comfortable. We also believe there are circumstances when separating conjoined twins is not in their best interests and that, in some cases, it is to the benefit of both patients and society that our understanding of what is “normal” is challenged.


In the case of “Jodie” and “Mary”, the Court of Appeal took the unprecedented step of endorsing a lethal assault on an innocent person, Mary. In brief, the case concerned the lawfulness of surgical separation which would have fatal consequences for Mary, because a number of vital organs on which Mary depended were contained within the skeletal structure of her sibling Jodie. Although the High Court and Court of Appeal judges differed in their legal reasoning, they all concluded it would be lawful to kill Mary in order to save Jodie. Synthesising the arguments of the appeal court judges, they thought that in these “unique” circumstances, killing Mary was a proportionate response to her sibling’s welfare requirements and that deliberately fatal surgery, which normally the law would regard as a murderous act, could, with recourse to legal principles, be transmuted into lawful homicide.

A crucial aspect of this case would have been how the judges conceptualised Jodie and Mary’s predicament. Was Mary a parasite putting Jodie’s life at greater risk? Was Jodie an individual with an unusual anatomy? Or were Jodie and Mary unique people requiring a unique response from the doctors and the courts? Despite the appeal court’s insistence that it was expounding law not acting as arbiter of morals, (Re A,1 969 d, per Ward LJ) the legal inferences that each judge was able to draw from the complex facts of the case would have been affected by their imaginative grasp of the dilemma. Did they approach this appalling predicament in terms that properly addressed its unique character, or did they cope by making it conform, inappropriately, to more tractable ethical and legal concepts?

All the judges involved in the case in the High Court and Court of Appeal made their decision on the basis that there were two independent minds, though enclosed within a single continuum of skin. Each twin presented with her own head, brain, lungs, and vital organs, but shared a torso, umbilicus, and bladder. In order to sustain their lives, however, they relied on the cardiovascular system largely located within the skeletal structure of Jodie. Both courts conceived of this as Mary relying on her twin Jodie’s heart and lungs for survival. As we argue in greater detail later in this article, we dispute the way in which the courts describe Mary’s relationship to Jodie, namely as a physical threat to Jodie through the former’s dependence for bodily survival on organs that, by implication, “belong” to the latter. We prefer to describe Jodie and Mary as having a “two in one” body, or bodily survival system, the components of which neither is free to dispose of as she pleases. Thus, the cardiovascular system on which the twins depend is not “Jodie’s” but forms part of “Jodie and Mary”. While the judges seem to assume that properly constituted individuals ought to have clearly circumscribed physical zones, we would argue that being in the conjoined state forms part of conjoined twins’ individuality. In so arguing, we are not adopting an “essentialist” view of the conjoined state, which would be prohibitive of separation surgery. Rather, we wish to highlight—where separation is called for—what is lost in separation.

In the High Court, Mr Justice Johnson seems to have made his decision on the legal premise that to split Mary from her sister would be analogous to recent cases involving the withdrawal of futile medical treatment, in the knowledge that the patient will almost certainly die as a result. To separate the twins surgically would not be to murder Mary, but rather to allow her to die, which the law allows in certain circumstances. The analogy with treatment withdrawal could be extended to splitting a child off from her organic life support system, her sister.

In the Court of Appeal, all the judges agreed that Jodie and Mary were each a person in their own right and therefore that each had a right to life. As each was “live born”—that is, born with a functioning brain, separate from their mother, and capable of sustaining independent existence, albeit with medical help, each fell to be protected by the law of murder.*

In English law, the fetus only acquires full legal protection when it is born and has a separate existence from its mother.2 This is the so called “liveborn” principle. There is no English case dealing directly with the degree of brain function necessary for birth. The better legal view, it is suggested, is that a person with a functioning brain stem can be “live born”, even if most or all the cerebral hemispheres—that is, the higher brain, are absent. Thus, it is not—for example, lawful to harvest the organs of anencephalic babies.

Mary was not merely a fleshy excrescence that could be separated off from Jodie without legal consequences. It was therefore necessary to reconcile her interests with Jodie’s, with whom she was bound together by flesh.

Brooke LJ appears to have derived his notion of bodily integrity (and inviolability?) directly from the sanctity of life doctrine: “the doctrine of the sanctity of life respects the integrity of the human body” (Re A,1 1051). He then seems to use a “natural rights” argument to justify fatal surgery: “The proposed operation would give these children’s bodies the integrity which nature denied them” (Re A,1 1051). Robert Walker LJ, going further, seems to equate the right to life with the “natural right” to physical integrity, which he interprets as the right to a whole, physically circumscribed, body, over which the legally competent patient would be sovereign: “Each twin’s right to life includes the right to physical integrity, that is the right to a whole body over which the individual will, on reaching an age of understanding, have autonomy and the right to self determination” (Re A,1 1066 j). Thus, restoring Mary’s bodily integrity, though it would kill her, was a “good end” which both disposed of the welfare issue and offered a defence to a charge of murder through the application of the doctrine of double effect. “This type of double effect cannot be relevant to conduct directed towards Mary unless the mere fact of restoring her bodily integrity, even at the moment of death, can be seen as a good end in itself and as something which ought to be achieved in the best interests of Mary as well as Jodie” (Re A,1 1063 e).

Although neither court defined with precision the ethical and legal status of Jodie and Mary’s fleshly bond, the assumption seems to have been that out of their entanglement of body parts, two singleton individuals could be “liberated”, though with fatal consequences for one of the twins. The assumption that Jodie and Mary had detached discrete interests that could be weighed into the balance is especially apparent in the judgment of Ward LJ. His view that the twins were meant to be physically separate people, of whom one (the “parasite” Mary), was unnaturally (and therefore perhaps unfairly?) attached to the other, is reinforced by the use of hypothetical cases—for example, Nazi commandants, (Re A,1 1009j-1010b) cliffhanging climbers, (Re A,1 1039 per Brooke LJ) and trigger happy six year olds, (Re A,1 1017b) designed to capture the predicament. He reconciles their competing interests through a search for the least detrimental alternative, which, in view of Mary’s supposed parasitic living, inevitably favours Jodie. Because Mary is “fated for death” she cannot be helped because she is “unnaturally supported” and treating her is “futile”, worthless, useless.

Were these court decisions responsible applications of legal principle that captured the ethical dilemma? Or does the judges’ reasoning represent a failure of the ethical and legal imagination? How did the court conceptualise the twins, and how should they have done? It is suggested that their lordships based their moral and legal reasoning on the anthropological premise that human beings are meant to be physically separate. As a result, they were led quite easily into using language that suggested that Jodie and Mary (or at least one of them) were in wrongful and harmful contact with each other. The judges might have viewed matters differently, notwithstanding that their decision would probably have been the same, if they had regarded Jodie and Mary’s conjoined state as part of a unique relationship requiring a unique response.


The three possibilities we consider could be applied to the case of any conjoined twins. The first will definitely only be applicable to some; the second and third are competing conceptualisations of twins who are both regarded as persons. While the second may seem more plausible in some cases and the third in others, we are primarily considering the possibilities with respect of Jodie and Mary’s particular situation.

The first possibility is that only Jodie is a person, and that Mary is just some extra flesh attached to her. If the term “parasitic conjoined twins” were taken in its medical sense, this is what it would mean. This scenario would present no ethical problems for separation since there would only be Jodie to consider. The second possibility is that the two should, by rights, be two physically separate people, singletons, who are by some accident joined together. This tends to see both Jodie and Mary as competing for the possession or use of body parts, and having competing and incompatible interests. The third possibility, and the one we would argue for, sees them, and all conjoined twins, as two individuals, psychologically separate but, by degrees, with a shared body. Here, their body is not something they are in competition over, but something they both have interests in, although neither has exclusive rights over it. Also, although they are “psychologically” individuals, part of what makes them the individuals they are is their conjoined state. This obviously raises questions about the sense in which they are individuals, and whether they would be the same or different individuals after separation, were this to take place.

Almost everyone would agree there are reasons for rejecting the first picture. We argue that although there are temptations to accept the second picture, the reasons in favour of it are difficult to justify philosophically, and tend to lead to deciding in favour of one twin to the detriment of the other. The third picture, we feel, offers the best way of understanding the reality of the situation facing conjoined twins. It also offers the best way of dealing with that situation while respecting both twins as the law and at least some ethical positions claim we should, without consideration of their individual mental and physical abilities or potential. In the next few sections we will consider each case in turn.

(i) Mary as a “parasitic” conjoined twin

Did or should the courts have considered Mary as part of Jodie’s body? This interpretation was not open to either court as a matter of law. Both twins had functioning brains, although there is evidence that Mary had suffered brain damage. Mr Justice Johnson, in the High Court, drew particular attention to Jodie’s brightness and alertness. Mary, in contrast, had a “very poorly developed primitive brain” and “reduced cortical development” (Re A,1 975 c per Ward LJ). Nevertheless, as a matter of law, Mary as well as Jodie was to be afforded all the legal protections appropriate to “liveborn” children.

Philosophically, most positions on the person would classify Jodie and Mary as the same. Either both would count as persons, since both are human (by which we mean biologically members of the species Homo sapiens) and alive. Or, according to theories which see as persons only those who have certain mental attributes (the ability to be self reflective, to plan their lives, to make moral decisions), neither would yet be a person. Many philosophical discussions on the nature of the person arise in the context of the abortion debate. For supporters of the first position see Noonan and Beckwith3,4 and for supporters of the second position see Feinberg, Warren, and Singer.5–7 The only way we might differentiate between Jodie and Mary in terms of personhood, is by taking account of their potential to acquire the capacities of a person. If we could say that Jodie could grow up to be a person, but Mary would never have the necessary capacities, we might think of them as having different moral statuses. One proponent of this sort of position is Don Marquis.8 He argues that what has moral standing in debates about abortion (and therefore about killing in general) is what has a future like ours. Here we could perhaps say that Mary is so badly damaged that she will never have a future like ours, and that perhaps it would not be wrong to kill her. Marquis does not address the question of badly damaged fetuses, infants or adults, so it is not clear whether he would hold this position with regard to Mary, but perhaps an argument along these lines could be constructed from his position.

One of the problems with that position, however, is that even a healthy, normally developing fetus has a higher moral status than many adults with mental problems, yet we are reluctant to say that such adults are not persons. Even if we were to think of Mary in this way, this may not allow us straightforwardly to prioritise Jodie’s interests over hers. And if we did it is hard to see that Mary would be classed as mere flesh; she would at least be granted the moral status of an animal.

If we think of them as two people, we still have a problem as to the role the body plays in the concept of a person. The next two possibilities consider whether each person should have their own separate body, or whether two people can share a body. These approaches broadly correspond to the “bodily distinctness” and “bodily relatedness” views described by Cathleen Kaveny in the search for a normative understanding of bodily integrity. Professor Kaveny argues that each view generates different criteria against which the ethics and law of separation surgery can be evaluated. This distinction draws attention to different anthropological premises that may underlie the medical, judicial, and parental thinking. It also provides a principled way of relating the particular issues raised by the case of Jodie and Mary to all cases of conjoined twins.9

(ii) Jodie and Mary as two entangled singletons

Did the courts, or should they, view Jodie and Mary as two individuals meant to be physically separate? It is clear, factually, that Jodie and Mary were never physically independent of each other until they were separated through the surgery that resulted in Mary’s death. They emerged as a result of a splitting process that was never completed. Thus, there is a “given-ness” about their conjoined state that makes it difficult to claim they were “meant to be physically separate” rather than were “meant never to have physically separated”. It seems clear, however, that the Court of Appeal felt it could only think of Jodie and Mary as singletons, physically separate individuals, in order to make an appropriate response. In other words, they seemed to have considered that the only way to think of them was as two separate individuals who were unfortunately joined together. The only model the courts seem to have for thinking about people and their best interests, is that of physically distinct individuals.

On one level, this is not surprising. The model of “one brain, one body” accords with the strong emphasis in the Western ethical and legal tradition on personal sovereignty. The ethical principle of autonomy is usually translated into negative terms as a right of non-interference, a right regulated—for example, by laws prohibiting non-consensual touching. Within this paradigm, the notion of individuality is linked to a separate body and anything else seems to be unimaginable, or at the very least, implausible. Physical separateness seems to be the indispensable condition for a life of dignity. Thus, physical separation seems to be the primary goal in the case of two persons in one body even if it leads to the death of one twin in certain circumstances. This would entail regarding the body, or parts of the body, as belonging to one of the twins, and the other twin as unjustifiably interfering with the first twin’s rights over her body. The appeal court’s reasoning could be interpreted as a perfectly intelligible expression of the association within the Western ethical and legal tradition between individuality and physical circumscription.

On another level, such reasoning causes problems. By treating Jodie and Mary as if they were singletons (physically separate), their lordships tended to resolve the predicament in a way that was detrimental to one of the twins. Actually, we argue that separation is detrimental to both twins, since they both lose part of themselves in the process. So conceiving of the twins as singletons both conceives of them as less than they are, and, since it regards separation as the primary aim, tends to ignore the loss to both of them in separation.

Conceptualising Mary as a “parasite” or one living “parasitically” suggests that Mary attached herself to Jodie for her own benefit. Here, we understand the word “parasite” to refer to a “live” twin, in contrast to its medical meaning, which refers to a fleshy outgrowth, which, while human in form is completely devoid of brain function.

The assumption is that Jodie and Mary ought “by rights” or “by nature” to have been physically independent. By treating them as if they had the discrete interests that are appropriate to physically independent people, those interests could be weighed into the balance and set off against each other with inevitable and deleterious consequences for Mary. By drawing moral and legal inferences on the basis of standard human physiology, the courts found it difficult to avoid conceptualising the twins as adversaries. This adversarial picture was evoked by Ward LJ in his startling speculation on what Jodie might have said to Mary had she been able to utter, “Stop it, Mary, you’re killing me”, and the vivid confrontational (Re A,1 1010 j per Ward LJ) analogies that the court used to capture the predicament.

This suggests that we think persons are somehow intended or meant to be singletons; that is, physically separate, one person to each body and vice versa. Not only does the law work within this paradigm, but so does medicine, and to some extent it has to. In order to deal with people’s medical problems we have to operate with some idea of how people are supposed to be. The question is: what idea. We have, and for some circumstances need, an idea of what counts as normal for humans. There are, however, many variations from the norm, some of which we find significant, some not. So is having a single body for two people an acceptable variation from the norm, or a defect that we need to do something about?

A recent philosophical attempt to argue that there is a way nature intended us to be may be found in Philippa Foot’s recent book, Natural Goodness.10 Here she argues that we can distinguish between variations from the norm for a living thing in terms of which characteristics are Aristotelian necessities, and which are not. If a creature lacks an Aristotelian necessity, then it is defective, but other variations from the norm are not defects. An Aristotelian necessity for a creature is a characteristic of that creature which it needs to live the type of life natural to its species. For plants and animals such characteristics are defined as those necessary for survival and reproduction.

Foot allows both that human lives are concerned with more than survival and reproduction, and that either of these can be rejected by humans in pursuit of what they consider a worthwhile life. So does a particular bodily shape, or even a body of one’s own, count as an Aristotelian necessity for humans? We argue that this is difficult to maintain. Of course conjoined twins are restricted in the things they can do, in the lives they can lead, and in the reproductive opportunities available to them. This is true, however, of all human beings in one way or another. The fact that being conjoined is statistically of low probability is not enough to make it a defect. Foot’s philosophical notion of defect—that is, not having characteristics which are Aristotelian necessities, bears a certain resemblance to the theological notion of ontic evil, instances of which may warrant human correction—for example, a baby being born without the capacity to see or physically joined to his or her sibling (Kaveny,10 note xii, pp 758—9). While, however, in the Roman Catholic tradition, bodily distinctness may be the moral norm of bodily integrity, in Foot’s analysis such distinctness does not seem to be a necessity in the Aristotelian sense. Neither can we rely on a distinction between what is a natural life, and what is artificially supported, as Foot can do in the case of plants and animals, since it is not clear what would count as natural for humans. Human society, and therefore what is natural for humans, changes as a result of development of human skills, knowledge, and ways of thinking. Admittedly conjoined twins might not even be born or survive without medical intervention. If, however, medical intervention is to count as unnatural, then many others might not survive who we would not consider defective. There seems to be no principled place to draw a boundary between the natural and the unnatural for human beings and therefore to distinguish between differences and defects. A similar argument is used by Ruth Garrett Millikan in her Language, Thought and Other Biological Categories: New Foundations for Realism.11 She argues:

The business of the biological species of staying in business determines standards for individuals of that species, standards which, though they often correspond to averages, are not defined in terms of mere averages over the species. Consider—for example, how few sperm or immature members of most species actually manage to perform all the functions that nonetheless are proper to them—that help account for the survival of the kind.

The evolution of a species is, however, related to an environment. Our point is that the human environment, within which we evolve, has, through medical science and public health, changed characteristics which would have been so disadvantageous as to preclude the survival of an individual long enough to reproduce. Such characteristics may still be disadvantageous, but they do not rule out survival and reproduction. Thus the standards for humans are determined in part by developments in human societies and sciences.

This is not to say that we would count nothing as a defect. When the question arises, however, it is not clear what should guide judgment.

If we cannot say clearly what should and should not count as defects for humans, and in particular whether a physically separate body is something to be aspired to, or as Robert Walker L J claimed, something to which we have a right, then can we, or should we, assume it is something we should aim for in dealing with conjoined twins? We now consider an argument that it is not, or at least not necessarily.

(iii) Two individuals with a shared body

In a seminal article,12 Alice Domurat Dreger argues that there needs to be a paradigm shift in the way that doctors (and by extension lawyers and the general public) view conjoined twins. She claims that the medical profession’s lust for intercision is driven by powerful cultural assumptions about what it is to be an individual, which often work against the best interests of conjoined twins (Dreger,12 p 25). It is suggested that her analysis can help us to elucidate some of the hidden assumptions that may have underlain the decisions of the English courts in the case of Jodie and Mary. Her view is that the strong association between individuality and physical separateness is culturally mediated and, in particular, mediated by the medical profession (Dreger,12 p4). The medical profession, when encountering unusually configured bodies, plays a pivotal role in deciding what the connection is between anatomy and identity. The meaning of “normal” physiology and individuality is construed and reified surgically in conformity with those prevailing cultural assumptions.

So powerful is the Western emphasis on physical separateness that the medical profession is unable to grasp the concept of a rich worthwhile conjoined life (Dreger,12 p 11). Dreger makes the startling observation that:

[Many twins] old enough to do so express a desire never to be separated [her italics] because it will result in such a profound change of identity or even the death of one’s other half. (Imagine having a vibrant part of your body amputated and lost forever, or else separated and left to lead an independent life!) (Dreger,12 p 10 and footnote).

In spite of copious evidence that conjoined twins do live lives they value, (see—for example, Smith,13 and Miller14) most doctors find the prospect of conjoined life highly undesirable. Not only are they willing to pursue potentially catastrophic surgery but they are lauded for taking modern surgical expertise to its limits.

For Dreger, however, all this begs a fundamental question: for whose sake is the operation carried out?

The paradoxical fact is that being conjoined is part of conjoined twins’ individuality [her italics]. If we singletons cannot understand that—if we cannot comprehend a life of two consciousnesses in one continuum of skin—that says something more about us than about them (Dreger,12 p 26).

The limits of individuality in the case of conjoined twins extend beyond the boundaries of the “standard” body. With reference to the work of Mary Douglas15 and Stephen Jay Gould,16 Dreger argues that the body is a flexible concept that cannot be pigeonholed into a discrete category. The accidental fact of conjoined twins puts the definition of individuality itself in issue.

Rather than looking at conjoined twins and noticing how much or how little autonomy singleton’s minds and bodies really possess—rather than letting their bodies challenge ours, rather than struggling with the question of what it ever means to have an individual mind or body in an intimate society—we choose to eliminate conjoined twins, to eliminate their accidental and profound questioning of the very concept of human individuality (Dreger,12 p 25).

This view seems to make a case for considering conjoined twins as two individuals, psychologically separate, part of whose individuality is constituted by being conjoined. That is to see them as essentially, rather than accidentally joined. This may encourage viewing their situation not as one in which each twin is a problem for the other, to be solved by contractual style negotiation, but where they both face a common problem and in which they have joint interests.

So viewing the twins as entangled singletons, and thus intended to be physically separate, suggests that the primary aim of medical intervention should be separation. Of course, this may not always be possible, as the recent case of Courtney and Natasha shows, and requires assigning organs which both may have enjoyed the use of to one twin or another. Courtney and Natasha May were discovered in utero to have separate umbilical cords leading to the placenta, separate arms, legs and head, but to share a four chambered heart, which was distorted and slightly larger than normal. Their parents had originally decided on separation, sacrificing Courtney. In the event, after birth it was decided that the operation was not feasible. In Jodie’s and Mary’s case, this view of separation as a benefit in its own right adds weight to balance the bad effect of Mary’s death.

Viewing them as two psychologically separate individuals with a shared body does not see physical separation as a primary aim; in fact it calls for recognition of what is lost in separation. As such, separation is one of the options to be considered when acting in the twins’ best interests. This position also calls for attempting to act in the best interests of both twins, not automatically balancing one person’s interests against the other’s.


The problem with the view of twins as entangled singletons is that it assumes something about the nature of human individuality (that having a body physically separate from that of others is an essential part of it) that cannot be philosophically justified. It sees conjointure as a defect to be corrected. If, however, we cannot distinguish between defect and difference, then conjointure surely has to be seen as something that may be a disadvantage in living life in our society, but may also have advantages. It might be argued that what seems advantageous to conjoined twins, only seems so because they cannot conceive of what it is to be separate, and this leads to a distorted view of the conjoined life. It could also be retorted, however, that we singletons cannot conceive of conjoined life and so also have a distorted view of it. We do not see things as they are, but as we are.

The two in one body view sees conjointure as a physical state that has both advantages and disadvantages, while recognising the value of the advantages. Since the disadvantages are a compound of the twins’ physical state and how our society is organised, it must surely be an open question whether the best compromise is to change conjoined twins physically to conform to society’s constraints and views, or to some extent to change the constraints and views of society to accommodate conjoined twins.

It seems that ethical and legal concepts designed to deal with confrontation are not always helpful in elucidating the nature of the conjoined relationship. Unlike most “contractual” relationships, which are premised on arrangements made between physically independent people, conjoined twins have an unbroken history of physical interdependence. There never was a time when they were not together. So it does not make sense to pretend that their conjoined relationship was something entered into through negotiation, or to treat it as something that can be broken on the assumption that their physical entanglement was not negotiated, as it were, “at arm’s length”.

There may well be an intimate relationship between the physical boundaries and the moral boundaries of conjoined twins. If being the individual you are, and if notions of privacy, autonomy, dignity, and individuality are all tied up with the bodies we inhabit, then surely the same should be true of conjoined twins. Dreger argues that their individuality certainly is, in that it is constituted in part by their intimate physical involvement with one another.

In an interesting thought experiment, in response to Judith Jarvis Thomson’s celebrated violinist analogy,18 Kenneth Himma explores this relationship in the case of hypothetical conjoined twins, known as Tom and Joe.19**

While Tom and Joe, who have survived to adulthood joined, could live a long and healthy life together, they cannot be separated without killing Tom, as all the vital organs are contained within the skeletal structure of Joe. The purpose of the thought experiment is to demonstrate that the unbroken history of physical interdependence, common to conjoined twins and the maternal fetal relationship, has moral implications not adequately accounted for by the “contractual” model applied by Thomson. Himma argues that because of that unbroken history, neither has unlimited freedom to dispose of “the shared continuum” as they please. Himma’s twins are adult, and able to decide for themselves. If, however, he is right, then it looks as if no one else may decide on behalf of conjoined twins to dispose of their body solely for the benefit of one and to the detriment of the other, as if one has more right to parts of it than the other. In Himma’s case all the vital organs are contained within what is identified as Joe’s skeletal structure, but they are still not his to dispose of. He has no right to deny Tom their use, since they have never been exclusively his. He argues that the contractual model, which sees the twins as separate agents with separate rights, is inappropriate to their situation and history. In a commentary on this argument Davis claims that what is important is not just an unbroken history of being joined, but the sharing of a body.20 Himma denies that the twins share a body, but Davis claims that if anyone does, they do, and as a result questions about the disposal of that body have to be settled in the light of the twins’ other interests.


Since parasitic conjoined twins do not seem to pose particular moral problems, our concern has been to explore the “entangled singletons” and “two in one body” models for conceptualising conjoined twins. We feel that the entangled singletons model does not do justice to the situation of conjoined twins, and has not, so far as we have discovered, been justified philosophically. It automatically favours physical separation as good in itself, and therefore tends to lead to decisions for surgical separation which play down its disadvantages and ignore the benefits of remaining conjoined. The two in one model reflects better the reality of conjoined twins’ situation. It also recognises the losses to twins in being physically separated and calls on us to attempt to resolve their situation without necessarily pitting them against one another, as even Kaveny does in her resolution of the predicament. Cathleen Kaveny’s solution to the problem of conjoined twins, even when this is recognised as a case of what she calls bodily relatedness, is to perform a species of utilitarian calculation comparing the benefits to one against the detriment to the other. We have two concerns with this. One is that it pits the twins’ interests against each other. The other is that it seems to assume that the twins are the same individuals before and after this calculation. Yet Kaveny herself recognises that “our bodies reflect and shape our identities” (Kaveny,9 p 758), so the two individuals in one body cannot be the same as the two individuals with separate bodies who are in some sense created by the separation surgery. This renders the aforementioned calculation not as simple as it looks.

It may be that in the case of Mary and Jodie, the decision would still come down on the side of surgical separation. And cases such as this, where separation will result in the death of one while giving reasonable prospect of healthy life to the other, are always going to be difficult. The difference our approach would make would involve not having to think of one twin as somehow preying on and being a problem for the other. This happens even where one is not noticeably worse off than the other is. In the case of the Lakenberg twins, the medical team painted their fingernails different colours to be sure of saving the right one, (Dreger,12 p 15) and initial talk of Courtney and Natasha, designated Courtney as the “passenger”. In both cases the twins shared a heart and were joined at the chest. The Lakenberg twins were separated, with the survivor nearly reaching her first birthday, although confined to hospital and on a ventilator. It was decided after birth that separation was not feasible for Courtney and Natasha. The main point, however, is that the Lakenberg twins were so indistinguishable that painted fingernails were needed to tell them apart, and Courtney seems to have been designated as a passenger, largely on the basis that it was thought more feasible to donate the shared heart to Natasha. In other words there is felt to be a need to designate one as posing a problem for the other even when this is not clearly the case. Perhaps it makes sacrifice surgery easier to contemplate if the child sacrificed is understood as threatening the potential survivor, however innocently, even though the grounds for saving one rather than the other may be pragmatic. Our approach would encourage seeing the twins as facing a common problem (which may need to be solved by surgical separation to the detriment of one of them) while attempting to value them equally and in order to act in the best interests of both. Their common physiology is a problem for both, and separation will create disadvantages for both, even for a survivor who might otherwise have died.

Of course, our approach is going to raise a host of problems, particularly for notions of individuality, identity, and responsibility. If we can have two individuals in one body, what are the limits of their individuality and identity? When they act, who is responsible for their actions. How does their autonomy function with respect to decisions about their body? What does privacy mean between two who are so intimately connected? Perhaps, however, these problems should be considered in the light of how they are resolved by those twins who have remained conjoined. The fact that such problems are raised by the existence of conjoined twins should perhaps be treated as a challenge to the rest of us to rethink our understanding of these concepts in general.

The ethical and legal thinking that treats conjoined twins as if they were physically separate entities who have unfortunately become entangled and need to have their separate existence restored, seems to have things the wrong way round. Conjoined twins are not separate and never have been. If we separate them, we should at the very least recognise that we are creating two new separate entities from two who were one, and that in doing so we are removing from each of them part of themselves. It may, of course, be a decision that we need to make for the benefit of both twins, but we should be wary of assuming that a physically separate existence is automatically in their best interests. If we are more comfortable faced by singletons, if they conform better to the hidden assumptions of our ethical, legal, and medical notions of what is normal and acceptable, That does not mean these are good enough reasons to change conjoined twins to fit. If medical decisions made on behalf of conjoined twins should be made in their best interests, then we had better be sure that they are, and that they are not made just because they make things easier for us to deal with. It is notable that it was in response to Jodie and Mary’s anatomical abnormalities that the Court of Appeal contributed some of the most stringent interpretations of bodily integrity in English law. The court’s reasoning is a good illustration of Canguilhem’s observation that “the abnormal, while logically second, is existentially first”.21††

We think that the abnormal is defined in terms of the normal, but in fact it is in the face of what is unfamiliar that we are prompted to define more clearly what is normal. This perhaps explains the appeal court’s strong affirmation of the connection between physical separateness and personal dignity. However, the unusual anatomy of conjoined twins could, and perhaps should, be taken as an opportunity to question that connection, and challenge our thinking about autonomy, privacy, dignity, and individuality.


We would like to express our thanks for the very helpful comments on earlier versions of this paper provided by the Revd Dr Andrew Goddard, Tutor in Ethics at Wycliffe Hall, Oxford and members of the Association of Teachers of Moral Theology at their meeting at Hinsley Hall, Leeds in May 2002. Its shortcomings, however, remain entirely our responsibility.



  • * In the context of conjoined twins, by “sustaining independent existence” we mean sustaining life independent of their mother, not of each other.

  • Later in the paper we will attempt to clarify in what sense conjoined twins might be thought of as “separate” and where that might be inappropriate. For now, we are using the term in a non-contentious way.

  • “Mary may have a right to life, but she has little right to be alive. She is alive because and only because to put it bluntly, but none the less accurately, she sucks the lifeblood of Jodie and she sucks the lifeblood out of Jodie. She will survive only so long as Jodie survives. Jodie will not survive long because constitutionally she will not be able to cope. Mary’s parasitic living will be the cause of Jodie’s ceasing to live. If Jodie could speak, she would surely protest, ‘Stop it, Mary, you’re killing me.’ Mary would have no answer to that. Into my scales of fairness and justice between the children goes the fact that nobody but the doctors can help Jodie. Mary is beyond help” (Re A,1 1010 h-j).

  • ** Thomson’s violinist analogy concerned a hypothetical famous violinist who is, for life saving purposes, surreptitiously attached to the healthy kidney of a dormant, unsuspecting surrogate. Thomson uses this analogy to sketch out the relationship between pregnant woman and fetus in essentially contractual terms.

  • †† This observation is also cited by Dreger (Dreger,12 p 5).

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