1. The (Supposed) Insignificance of Identity

Many issues and arguments in bioethics bring together difficult questions in ethics and in metaphysics, including – at least on the face of it – the metaphysics of identity. Consider Don Marquis's well-known future-like-ours argument for the claim that ‘abortion is prima facie seriously morally wrong’ (Reference Marquis1989, p. 192). Marquis's argument consists of two premises. First, killing an adult human is prima facie seriously wrong because in general it is prima facie seriously wrong to deprive something of a future like ours (a FLO) – a future filled with the ‘activities, projects, experiences, and enjoyments’ that, typically, make our lives valuable (p. 189). Second, abortion deprives something – a foetus – of a FLO. The second premise seems to have implications for the identity conditions of foetuses: e.g., that each of us was once a foetus; that, in a typical, full-length pregnancy, the foetus is identical with something that, later on, experiences a life like ours; and so on.

One way in which the metaphysics of identity seems relevant to Marquis's argument is revealed by an objection the argument faces. Standard accounts of personal identity typically fall into one of two categories: psychological accounts say that psychological continuity of some sort is necessary and sufficient for a person's identity over time; biological accounts say that biological continuity of some sort is necessary and sufficient.Footnote ¹ Many philosophers (e.g., McMahan, Reference McMahan2002; Manninen, Reference Manninen2007; Heathwood, Reference Heathwood2011) have argued that Marquis's argument requires commitment to a biological account since – in the first trimester, when most abortions occur (Lee et al., Reference Lee, Peter Ralson, Drey, Partridge and Rosen2005) – foetuses lack psychological traits and therefore cannot be psychologically continuous with future experiencers of lives like ours. The objection from opposition to biological accounts of identity, then, begins with the rejection of biological accounts of identity and infers from this that Marquis's argument fails.Footnote ²

Some philosophers have argued, however, that – irrespective of the plausibility of objections like the above – the success of Marquis's argument does not importantly turn on the metaphysics of identity. Earl Conee argues that Marquis's argument doesn't turn on metaphysics at all, in the sense that ‘the metaphysics congenial to Marquis's position provides no support for any particular moral conclusion about abortion’ (Reference Conee1999, p. 644).Footnote ³ Meanwhile, David Shoemaker argues that Marquis's view about abortion ‘isn't non-derivatively dependent on conclusions about numerical identity’ (Reference Shoemaker2010, p. 485). And Tim Burkhardt defends an objection to Marquis that, he says, ‘has force regardless of which account of personal identity is true’ – and that, more generally, is intended to float free of the metaphysics of identity – but that also does not directly challenge Marquis's explanation of the wrongness of killing (Reference Burkhardt2021, p. 3).

My aim in what follows is modest. I argue that the success of Marquis's argument does importantly turn on the metaphysics of identity. This is not to say that the metaphysics of identity is the only issue on which Marquis's argument turns. Rather, the success of Marquis's argument turns on (the truth of) precisely two things: first, Marquis's claim that it is prima facie seriously wrong to deprive something of a future like ours;Footnote ⁴ second, the claim that, in a counterfactual circumstance in which an abortion does not occur, the entity that is at one time a foetus is (numerically) identical with something that, later on, experiences a life like ours. Going forward, I shall sometimes put this second claim more simply as follows: absent an abortion, the foetus would be identical with an experiencer of a life like ours – for short, to an experiencer.Footnote ⁵ While only this second claim is (straightforwardly) about the metaphysics of identity, the first claim – while disputable – is certainly plausible. So, if the second claim is true, then its truth counts significantly in favour of Marquis's argument.

In what follows I offer first a negative and then a positive defence of my position. In §2 I consider what I take to be the most promising case for the claim that Marquis's argument does not importantly turn on the metaphysics of identity. This is Burkhardt's objection. I argue, pace Burkhardt, that his objection essentially depends on the failure of biological accounts of identity. In §3 I consider and reject a potential way of resisting my argument in §2, and in the process of doing so I characterize a philosophical dispute that plays an important role in the remainder of the paper. This is the dispute between endurantist and perdurantist views of persistence. In §4 I advance my positive argument. One upshot of this argument is that Burkhardt's objection fails outright. The more important upshot, again, is that Marquis's argument importantly turns on the metaphysics of identity in the way discussed above. I end in §5 by discussing the relationship between my arguments and the question of what matters in survival.

2. Identity Matters in Burkhardt's Fission Argument

Recently, Tim Burkhardt (Reference Burkhardt2021) has defended an objection to Marquis that does not challenge Marquis's explanation of the wrongness of killing but that also purports to float free of the metaphysics of identity. Burkhardt's objection is that, if abortion wrongfully deprives a foetus of a FLO, then – absurdly – contraception wrongfully deprives a sperm and an ovum each of a FLO. Like the objection from opposition to biological accounts of personal identity, Burkhardt's objection is aimed at disputing the idea that a foetus's biological continuity with an experiencer (of a life like ours) is enough to show that abortion deprives a foetus of a FLO. However, Burkhardt does not dispute biological accounts of identity or any other claim about the identity conditions of foetuses. Rather, Burkhardt seeks to show that Marquis's argument fails even if (counterfactually) foetuses are identical with experiencers. That is, according to Burkhardt, ‘the fundamental problem with Marquis's argument […] is not his view that identity across time is a matter of merely biological relations, but his investment of those relations with moral significance’ (Reference Burkhardt2021, p. 3).

Burkhardt's objection consists of his considering, and disputing, actual or possible attempts at identifying what I'll call ‘a morally relevant difference between foetuses and gametes’ – more precisely, a difference between foetuses and gametes that explains why abortion deprives foetuses of FLOs but contraception does not deprive gametes of FLOs. Burkhardt begins with Marquis's attempt at identifying such a difference (Reference Marquis1989, Reference Marquis2002). The difference, Marquis says, is that a sperm and an ovum are two things, whereas a foetus is one. This difference is morally relevant because (typically) a successful pregnancy results in only one future and because two things cannot be deprived of the same future (Marquis, Reference Marquis1989, p. 201; Reference Marquis2002, pp. 77–8).

According to Burkhardt, Marquis's explanation commits him to three (jointly) conflicting claims. The first is that – as I'll put it – identity is necessary for deprivation, i.e., necessarily, an event deprives an entity of a FLO only if, absent that event, that entity would have, eventually, experienced a life like ours (Reference Burkhardt2021, pp. 3–5).Footnote ⁶ Since identity is transitive (and symmetric), two nonidentical entities could not both be identical with whatever, absent contraception, goes on to experience a life like ours. So, if identity is necessary for deprivation, then two things cannot be deprived of the same future. On the other hand, if identity is not necessary for deprivation, then it's not clear why two things – a sperm and an ovum, for instance – cannot be deprived of the same future.

The second claim is that a biological continuity account of identity is true. Again, since foetuses at the time of (most) aborted pregnancies do not have psychological traits, Marquis's claim that abortion deprives foetuses of FLOs – together with his commitment to the claim that identity is necessary for deprivation – commits Marquis to denying psychological accounts of identity and to accepting, instead, a biological account (Reference Burkhardt2021, pp. 5–6).

The third claim is what Burkhardt calls the ‘uniqueness requirement’: the claim that ‘for any two human organisms who are biologically continuous with each other, these organisms can be identical only if the relevant continuity relation does not take a branching form’ (Reference Burkhardt2021, p. 7). This claim is really a corollary to, and indeed an implication of, the second. Any plausible biological account of identity must come with a specific conception of what exactly the relation of biological continuity that is necessary and sufficient for identity amounts to (e.g., a causal process of a certain sort, or sameness of certain biological features, or something else). Moreover, since identity is transitive (and symmetric), this conception must include (or at least imply) the requirement that the relevant biological continuity relation be non-branching, i.e., that, necessarily, for any person x and any y, x is identical with y if and only if x (at a time) is biologically continuous with y (at a time) and with nothing else.Footnote ⁷

According to Burkhardt, these three commitments together commit Marquis to something unacceptable: namely, that whether or not something can be deprived of a FLO depends entirely on whether it stands in a biological continuity relation that is non-branching. According to Burkhardt, ‘[e]ven if we grant that merely biological relations are morally relevant with respect to deprivation, it strains the imagination to think that a being's ability to be deprived of a future could depend on whether or not it stands in such relations uniquely’ (Reference Burkhardt2021, p. 7). To demonstrate Marquis's commitment to this and to argue that such a commitment is unacceptable, Burkhardt presents the following scenario:

Burkhardt argues, first, that – in the counterfactual circumstance in which an abortion does not occur but fission does – Fiona is not identical with anything existing after her fission (pp. 7–8). Again, in this circumstance, Fiona is biologically continuous with two postnatal human beings. Since identity is transitive (and symmetric), ‘Fiona cannot be identical to both of these human beings’ (p. 7). But, nor, it would appear, could she be identical with precisely one of them, since it would be wholly arbitrary which one. Nor are there any other plausible candidates with whom Fiona may be identical – e.g., she is not identical with ‘some third thing composed of the union of the two’ (p. 7). So, Burkhardt concludes:

Burkhardt argues, second, that – even though counterfactually Fiona is not identical with an experiencer (of a life like ours) – her (actual) Monday-scheduled abortion still deprives her of a FLO, at least assuming – as Marquis must – that biological continuity (of the appropriate sort) is sufficient for identity and, accordingly, for deprivation. In the counterfactual scenario, ‘Fiona stands in two biological continuity relations – call them R₂ and R₃ – to two distinct experiencers’ (p. 8). Assuming that standing in a biological continuity relation to a single experiencer is sufficient for deprivation (as Marquis must assume), ‘if Fiona stood in just one of them (say, just R₂), then […] aborting Fiona would deprive her of a valuable future’ (p. 8). But:

Consequently, Burkhardt asserts:

Thus, Burkhardt concludes, if Fiona's (counterfactual) biological continuity with a single experiencer is sufficient for deprivation, then so too is her biological continuity with multiple experiencers. But, then, identity is not necessary for deprivation after all.

Call Burkhardt's overall argument against Marquis's explanation ‘the Fission Argument’. Notice that Burkhardt, in advancing this argument, does not explicitly reject biological accounts of identity. So, it may appear – as Burkhardt himself would insist – his argument is consistent with such views.

But here appearances are deceiving. Philosophers have often observed that fission scenarios pose a challenge to continuity accounts of identity precisely because these accounts seem to conflict with the fact that identity is transitive (and symmetric). The Fission Argument is really a variation on – and, I shall argue, ultimately relies on the same principles underlying – a traditional argument that rejects biological accounts (and continuity accounts more generally) on these grounds.Footnote ⁹

To begin to see this, return to Burkhardt's key inference from No Difference to No Effect. This straightforwardly relies on the following:

If Link is true (and should be endorsed), then this is because the following is true (and should be endorsed):

Link is highly plausible. But so is Existence: how could Fiona's continuing to exist plausibly depend on some other, causally irrelevant thing's not existing? More to the point, say that Existence is false. Then so is Link. For the plausibility of Link derives from the fact that, since R₃ makes no intrinsic difference to R₂, there at least seems to be no plausible explanation for how the addition of R₃ could make a difference as to whether abortion deprives Fiona of a FLO. But, if Existence is false, then the mere (counterfactual) addition of R₃ does make a difference as to whether abortion has deprived Fiona of a FLO, and we now have a straightforward, principled explanation for why: in the counterfactual circumstance in which R₃ obtains, Fiona won't continue to exist and, accordingly, won't go on to experience a life like ours! So, abortion doesn't deprive her of anything! So, Link is true only if Existence is true. Say, then, that Link is true. Then Existence is true. Moreover, in this case, the truth of Existence explains the truth of Link. Link is true because the mere addition of R₃ (in the counterfactual case in which there is no abortion) makes no difference as to whether abortion deprives Fiona of a FLO precisely because it makes no difference as to whether (in this counterfactual case) Fiona would go on to experience a FLO.

To summarize, Burkhardt's crucial inference from No Difference to No Effect relies straightforwardly on Link, which – I've just argued – relies on Existence.

It follows that Burkhardt's Fission Argument ultimately relies on principles that, by themselves, constitute an argument against biological accounts of identity. To tailor this argument to Burkhardt's case involving Fiona (in circumstances not involving abortion), we might present the argument as follows:

Call this argument the Existence Argument. While I have cast the Existence Argument in terms of Burkhardt's scenario involving Fiona, this argument needn't be cast in these terms. It may centre on the division of any entity of the sort that can, at least in non-fission cases, stand in whatever biological relation is proposed to be sufficient (and necessary) for identity. For instance, Peter van Inwagen considers a version of this argument centring on an intelligent amoeba with two centres of bodily control (Reference Unger1990, pp. 202–12). So, the Existence Argument, in its essence, is not new. Moreover, and more importantly, the Existence Argument ultimately relies on a total of three principles: Counterfactual, No Difference, and Existence. Burkhardt's Fission Argument explicitly relies on Counterfactual and No Difference. And Burkhardt's crucial inference from No Difference to No Effect ultimately relies on Existence. So, Burkhardt's Fission Argument ultimately relies on principles that, by themselves, constitute an argument against biological accounts of identity.

Here is one consequence of this fact: any successful objection to this argument against biological accounts will also undermine the Fission Argument. For instance, one plausible way to respond to the Existence Argument is to characterise what biological continuity of the appropriate sort is in a way that is independently plausible and that plausibly entails that branching scenarios will not obtain (but without one's simply stipulating that the biological continuity relation must be non-branching).Footnote ¹² For instance, van Inwagen characterises biological continuity in terms of having the same life, and as van Inwagen understands what it is to have a life (a biological process of a complex sort), the process of fission would inevitably disrupt a life (Reference van Inwagen1990, pp. 148–9 and pp. 202–12). So, van Inwagen rejects (or would reject) No Difference. If No Difference is false, Burkhardt's Fission Argument fails.Footnote ¹³

Here is another consequence, one that immediately follows. Recall that Burkhardt's Fission Argument seeks to show that Marquis's explanation of the morally relevant difference between foetuses and gametes fails. It turns out that, pace Burkhardt, the success of the Fission Argument – and, accordingly, of Burkhardt's objection to Marquis – depends on the failure of biological accounts of identity (and, moreover, does not advance a new objection to such accounts). For, if a biological account of identity is correct, then the Existence Argument goes wrong somewhere. And, if the Existence Argument goes wrong somewhere, then – as I've argued above – so does Burkhardt's Fission Argument.

3. Fission and the Metaphysics of Persistence

The success of my response to Burkhardt turns on the success of my argument that, if Link is true, its truth is explained by the truth of Existence. This may be disputed. But disputing it essentially involves an appeal to a view of persistence that proponents of the Fission Argument must deny. Let me explain.

Perdurantism says that persons and other ordinary material objects persist by perduring. Take me, for instance. For me to perdure is for me to exist at various times by having temporal parts located at those times. For any time t at which I am located, my t-located temporal part, or stage, is the thing that (i) is located precisely at t, (ii) is my part at t, and (iii) overlaps (shares a part with) each part I have at t.Footnote ¹⁴ For instance, my noon-located temporal part, or noon-located person-stage, is located at noon and nowhen else, is a part of me at noon, and overlaps each part I have at noon. Perdurantists standardly explain property change by holding that my temporary property instantiations are derivative on the property instantiations of my temporal parts: for any time t and temporary property F such that I am F at t, my being F at t amounts to my t-located stage's being F. For instance, if I feel awake at 7 pm but feel sleepy at 11 pm, that amounts to my 7-pm-located stage's feeling awake and my 11-pm-located stage's feeling sleepy.

Perdurantism's main rival is endurantism.Footnote ¹⁵ Endurantists say that persons and other ordinary material objects persist by enduring. For me to endure is for me to exist at various times but not by having different temporal parts at those times. Rather, if I endure, then for any time at which I exist, I am wholly present at that time, in the sense that all of the parts I have simpliciter exist at that time. Since endurantists deny that I have (proper) temporal parts, they cannot appeal to temporal parts to explain my temporary property instantiations. Rather, endurantists must maintain that when, for instance, it is 7 pm, I myself (non-derivatively) have the property of feeling awake, and that four hours later I myself will (non-derivatively) have the property of feeling sleepy.Footnote ¹⁶

Now return to my argument that, if Link is true, it is true because Existence is true. This argument is hard to resist given endurantism. For, given endurantism, in the counterfactual circumstance in which Fiona is at one time a foetus and at a later time an experiencer, it really is Fiona who (non-derivatively) experiences joy, (non-derivatively) performs actions in pursuit of meaningful projects, etc. It is hard to deny that, in this case, the answer to whether abortion deprives Fiona of a FLO turns on – and is explained by – the answer to whether (counterfactually) Fiona herself eventually experiences a life like ours. But say, instead, that perdurantism is true. Then, in the counterfactual circumstance in which Fiona is identical with an experiencer, this just amounts to Fiona's having a number of well-after-birth-located person-stages that experience joy, perform actions in pursuit of meaningful projects, etc. In this case, it seems at least plausible to assert that the answer to whether abortion deprives Fiona of a FLO does not turn on – and isn't explained by – the answer to whether, counterfactually, Fiona is identical with an experiencer.

Or so one may argue. In §4, I'll argue that my argument in §2 succeeds even given perdurantism. But for now I wish to observe that, even if the above-presented objection to my argument succeeds, it is not available to proponents of the Fission Argument.

Return to Burkhardt's original scenario: Fiona goes out of existence on Monday as a result of an abortion; had the abortion not occurred, on Tuesday Fiona would have undergone fission. Remember that a key to Burkhardt's argument is that, in the counterfactual scenario, Fiona stands in two biological continuity relations, to two separate experiencers. And remember that another key is that, in yet another counterfactual scenario in which neither the Monday abortion nor the Tuesday division occurs, Fiona stands in just one biological continuity relation, to just one experiencer. Call the former ‘the Two-Relations scenario’ and the latter ‘the One-Relation scenario’. Burkhardt wants to say that whether abortion deprives Fiona of a FLO cannot depend on whether, absent the abortion, the One-Relation or the Two-Relations scenario obtains. But assume perdurantism. Then we cannot consistently maintain that Fiona herself exists, even briefly, in both of these scenarios. Let's grant that she exists in the One-Relation scenario. Then, given perdurantism, in this scenario Fiona is a four-dimensional ‘worm’ composed of stages located from a time at or after conception to a time, say, 80 years later. In the Two-Relations scenario, on the other hand, there are two four-dimensional worms – call them ‘Fiona₁’ and ‘Fiona₂’ – both about 80 years long (they needn't be the same length, really) and overlapping at all (and only) times up to the Tuesday division. Neither Fiona₁ nor Fiona₂ is Fiona; Fiona simply does not exist in this scenario.Footnote ¹⁷ So, we still have – pace Burkhardt – an extremely compelling reason for claiming that the answer to whether abortion deprives Fiona of a FLO depends on the answer to whether, absent the abortion, it is the One-Relation or the Two-Relations scenario that obtains: in the Two-Relations scenario, Fiona doesn't even exist and, a fortiori, doesn't stand in any biological continuity relations!

So, if perdurantism is true, the Fission Argument fails, whereas my argument in §2 succeeds assuming endurantism. Here's another way to put this: if endurantism is true, then Burkhardt's objection to Marquis fails provided that a biological account of identity is true; if perdurantism is true, then Burkhardt's objection fails outright.

4. Identity Matters in Deprivation

I shall now argue that the success of Marquis's argument depends precisely two things: first, whether it is seriously wrong to deprive something of a FLO; second, the identity conditions of foetuses in counterfactual scenarios.

I'll begin by explaining – and justifying – two terminological choices.

First, by ‘is identical with’ I mean is numerically identical with. At one point, Burkhardt suggests that by ‘is identical with’ (or ‘is identical to’) he means, instead, is a stage-mate of, where x is a stage-mate of y just in case x and y are temporal parts of the same individual.Footnote ¹⁸ If so, this is problematic for a couple reasons. First, it rules out endurantism by fiat. Second, recall from §2 that Burkhardt's Fission Argument relies on the idea that identity is transitive. Numerical identity is transitive; the stage-mate of relation is not.Footnote ¹⁹ Third, again, Marquis holds that an abortion deprives a foetus – call it ‘A’ – of a FLO since, absent the abortion, A would have, eventually, gone from being a foetus to being (years later) an experiencer (Reference Marquis2002, pp. 77–8). This at least makes sense if we understand A's eventually experiencing a life like ours as A's being numerically identical with something that at one time is a foetus and at a later time experiences a life like ours. But if, instead, we take A (absent an abortion) to be a mere stage-mate of an experiencer, then (at least by Marquis's lights) it doesn't make sense to say that A can be deprived of a FLO. For, in this case, even absent the abortion, A itself would not have experienced a life like ours.Footnote ²⁰

Since my goal is to evaluate Marquis's argument and to explore what it depends on, I should use ‘is identical with’ in a way that allows me to make charitable sense of Marquis's argument. So, I use ‘is identical with’ to mean is numerically identical with, not is a stage-mate of.

Note that proponents of both views of persistence discussed earlier can follow me in using ‘is identical with’ to mean is numerically identical with and, in doing so, to make plausible sense of Marquis's commitments regarding the (counterfactual) identities of foetuses. Consider an arbitrary example of a typical abortion: on Monday, an abortion occurs, ending the life of a foetus – say, Fete. Now consider the counterfactual circumstance in which the abortion doesn't occur and the pregnancy goes full term, eventually resulting in a certain individual's experiencing a life like ours. Call this individual ‘Pete’, and – to keep things simple – let t* be one of the many times at which Pete enjoys a particular experience, performs a particular action, etc., that is part of this life like ours. For instance, say that, at t*, Pete experiences joy. Marquis will say – and is committed to saying – that, in this counterfactual circumstance:

Endurantists should understand this description as follows:

Perdurantists, meanwhile, should understand the description as follows:

Notice that, for perdurantists, in the counterfactual circumstance, Fete himself is not identical with a foetus but, rather, has a proper temporal part that is a foetus.

So, again, by ‘is identical with’ I mean is numerically identical with, and in adopting this usage I am able to make charitable sense of Marquis's argument. Moreover, I can do so without presupposing a particular account of persistence.

Here's my second terminological choice. I characterise deprivation as follows:

where

My understanding of deprivation captures the sense in which, according to Marquis, depriving something of a FLO is (prima facie) seriously wrong. This is the sense in which, according to Marquis, killing an adult human is (prima facie) seriously wrong. Again, killing an adult human is seriously wrong, for Marquis, because doing so deprives that individual of a FLO. It is seriously wrong to deprive an individual of a FLO because doing so is bad for that individual, and doing so is bad for that individual because it involves preventingFootnote ²⁵ something that is (to the same extent) good for that individual – namely, the experiencing of a life like ours. (See Marquis, Reference Marquis1989, pp. 189–90.) But how good? Well, good to the extent that a typical life like ours is good. This is what I shall mean by ‘good’ going forward.

Consider an arbitrary individual – say, Serena – and an arbitrary time – say, next Monday. In what circumstances does Serena possess a post-Monday life like ours?

Say that, over some period of time after Monday, Serena herself experiences a life like ours. Then, at various times after Monday, Serena has the experiences, pursues the projects, etc., that (typically) make life valuable. But valuable for whom? Well, for Serena! So, if (after Monday) Serena experiences a life like ours, then her doing so is good for her. So, if (after Monday) Serena experiences a life like ours, then there is an individual y (namely, Serena) such that (after Monday) y experiences a life like ours and y's doing so is good for Serena. So, if (after Monday) Serena experiences a life like ours, then Serena possesses a post-Monday life like ours.

Are there other circumstances in which Serena may possess a post-Monday life like ours? Perhaps not. But there are some candidates. Perhaps Serena possesses a post-Monday life like ours if Serena, at some time or other, is a devoted mentor to or a loving parent, friend, etc., of someone who, after Monday, experiences a life like ours. Or perhaps Serena possesses a post-Monday life like ours if Serena, at some time or other, is psychologically continuous with someone who, after Monday, experiences a life like ours. These exhaust the possibilities. And notice that all of these possibilities involve situations in which Serena herself also counts as, at some time or other, experiencing a life like ours. Or at least they must if we are to count such things as being good for Serena, which we must if we are to count such things as ways in which Serena possesses a post-Monday life like ours. It follows that Serena possesses a post-Monday life like ours only if, over some period of time or other, Serena herself experiences a life like ours.

To conclude, since ‘Serena’ is an arbitrary name, and since my argument relies on nothing contingent:

The most promising way of disputing my argument for Possession involves perdurantism. Recall that, in experiencing a life like ours over a period of time after Monday, Serena – after Monday – has the experiences, pursues the projects, etc., that (typically) make life valuable. The key move in my argument is from this claim to the claim that these experiences, projects, etc., make life valuable for Serena. This inference is indisputable given endurantism. For, given endurantism, Serena herself non-derivatively has these experiences, performs actions in pursuit of these projects, etc. However, given perdurantism, it is not Serena but rather her post-Monday-located temporal parts that non-derivatively have these experiences, perform these actions, etc. In this case, it seems at least plausible to say that, while Serena's experiencing a post-Monday life like ours is valuable, it is not valuable for Serena – rather, it is valuable for various of her post-Monday-located temporal parts.Footnote ²⁶

The problem with this objection is that it cannot plausibly be accepted by perdurantists. Begin with the observation that, just as a conceptual truth, a life like ours is a life experienced – that is to say, a life lived – by a person. So, in assuming that Serena herself experiences a life like ours, we assume that Serena is a person. Now, perdurantists say that persons are aggregates of temporal parts, not temporal parts themselves. That's the view. So perdurantists must say that there is at least one property that Serena has non-derivatively: personhood. Given their view that a person's having a property at a time t just is that person's t-located stage's having that property, perdurantists should say that Serena has the property of personhood timelessly. What other properties should perdurantists say that Serena, as a person, has non-derivatively and, accordingly, timelessly? Another such property must be living a life that is valuable for her. For, to begin, plausibly, it is just part of the concept of a person that a person is the appropriate object of moral and practical concern. This requires that a person is an entity of a sort for which things stand to go well (or badly). Second, and to my mind more importantly: consider things from the first-person perspective. When I engage in practical reasoning, I – the person – make decisions partly based on what I believe is good for me, not just at a particular time but overall. But this is rational only given that I, the person, am a thing of the sort for which certain things – my life, at the very least – can be good (or bad). So, even perdurantists must say that Serena, and not her person-stages, is the one for whom a life like ours is valuable.

So, Possession is true. It follows that, at least with respect to prenatal beings, identity is necessary and sufficient for deprivation. By ‘prenatal beings’ I mean foetuses and gametes and any other things of the sort that exist before human births and that are in some sense biologically continuous with postnatal humans. Moreover, let a ‘continuity-disrupting’ event be any event – an abortion, an instance of contraception, or something else – the result of which is that a certain prenatal being (or beings) never ends up standing in a biological continuity relation to a postnatal human (i.e., a birth does not occur). Let Disruption be one such event – occurring on Monday, say – and let Venus be the (or a) relevant prenatal being. Has Disruption deprived Venus of a FLO? It depends on what would have been the case, had Disruption not occurred.

First, assume that, in the counterfactual scenario in which Disruption does not occur, Venus herself, eventually, experiences a life like ours. Venus's experiencing this life takes place over some period of time after Monday, of course. It follows by Possession (i, the sufficiency clause) that Venus possesses a post-Monday life like ours. But, of course, in the actual scenario, in which Disruption occurs, there is no time period over which Venus experiences a life like ours. It thus follows by Possession (ii, the necessity clause) that, in the actual scenario, Venus does not possess a post-Monday life like ours (or a post-any-other-time life like ours, for that matter). It thus follows by our definition of ‘deprivation’ that Disruption has deprived Venus of a FLO.Footnote ²⁷

Now assume that, in the counterfactual circumstance in which Disruption does not occur, it is not the case that Venus, eventually, experiences a life like ours. It follows by Possession (ii, the necessity clause) that, in this counterfactual circumstance, Venus does not possess a post-Monday life like ours. It follows that Disruption does not count as having deprived Venus of a FLO.

So, Disruption deprives Venus of a FLO if and only if, had Deprivation not occurred, Venus would have, eventually, experienced a life like ours. So, to conclude (since our example is arbitrary and since nothing in the argument relies on anything contingent):

Deprivation has several important consequences.

First, it confirms my analysis of Burkhardt's argument. In §2 I argued that – pace Burkhardt – the success of Burkhardt's Fission Argument depends on the failure of (all) biological accounts of identity. My argument turned on my claim that, if abortion's depriving Fiona of a FLO cannot depend on whether (counterfactually) Fiona stands in R₂ uniquely (Link), then this is because Fiona's continuing to exist past Tuesday cannot depend on whether Fiona stands in R₂ uniquely (Existence). I demonstrated in §3 that my claim is true at least given endurantism and that, if perdurantism is true, Burkhardt's argument fails outright. Deprivation implies that my claim is true even given perdurantism. So, Deprivation gives us another reason to see that my argument is sound and, accordingly, that the success of Burkhardt's Fission Argument depends on the failure of biological accounts of identity (as well as on the falsity of perdurantism).

Second, Deprivation shows that Burkhardt's overall objection to Marquis fails outright. Deprivation entails that abortion deprives a foetus of a FLO, provided that a biological account of identity is true and that, accordingly, absent an abortion a foetus would be identical with something that (later on) experiences a life like ours. Deprivation also entails that – since a sperm and an ovum are two things and as such cannot be identical with a single experiencer of a life like ours – contraception does not deprive a sperm and an ovum of a FLO. So, Deprivation entails that, if the above-italicized condition is met, Marquis's explanation for the morally relevant difference between a foetus and gametes is correct. But now recall that Burkhardt's ultimate goal is to show that ‘the fundamental problem with Marquis's argument […] is not his view that identity across time is a matter of merely biological relations, but his investment of those relations with moral significance’ (Reference Burkhardt2021, p. 3, my emphasis). This is false. Either Marquis is wrong to hold ‘that identity across time is a matter of merely biological relations’ (including in a counterfactual circumstance in which an abortion does not occur) or he is right to invest those relations with moral significance.

A third consequence immediately follows. Marquis's future-like-ours argument succeeds if and only if two principles are true: first, depriving something of a future like ours is prima facie seriously wrong; second, in a counterfactual scenario in which an abortion does not occur, the foetus is (numerically) identical with something that, later on, experiences a life like ours.Footnote ²⁸ Deprivation takes us from the second principle to the claim that abortion deprives foetuses of FLOs. It follows from this and the first principle that abortion is prima facie seriously wrong.

5. Conclusion: What Matters

It has been claimed that, despite appearances, the metaphysics of identity – particularly as it involves foetuses – is not of central importance to the success of Marquis's well-known future-like-ours argument. This claim is false. Marquis's argument succeeds if and only if (i) depriving something of a FLO is prima facie seriously wrong and (ii), in a counterfactual scenario in which an abortion does not occur, the foetus is (numerically) identical with something that, later on, experiences a life like ours. In the process of demonstrating this, I have considered what to my mind is the most promising attempt at showing that Marquis's argument fails even if (i) and (ii) are true. I have shown that this attempt is unsuccessful.

I shall end by commenting on the relationship between what I've been discussing and the question of what matters in survival. For typical human persons, ordinary survival involves or is accompanied by a number of relations. Among these are relations of biological continuity, of psychological continuity, and of identity. Which of these relations fundamentally matters, practically (and morally) speaking? Consider Kate, who goes by ‘Katie’ in childhood and by ‘Katherine’ in old age. Say that Katie, as a child, works hard in school because she has a special interest in the welfare of Katherine in old age. What makes this special interest rational? One natural answer is this: the fact that Katie just is – is numerically identical with – Katherine. Many philosophers provide a different answer. They answer: the fact that Katie in childhood is psychologically continuous with (or psychologically connected to) Katherine in old age. In other words, these philosophers say that what fundamentally matters in survival is not identity but, rather, psychological continuity (or connectedness).Footnote ²⁹

There is an important sense in which my discussion above is related to the question of what matters in survival. Indeed, we might even characterize my argument in §4 as providing an answer to an analogous question, namely: in virtue of what does someone or something count as possessing a life like ours? Call this the question of ‘what matters in possession’. My answer: someone or something counts as possessing a life like ours in virtue of being numerically identical with whatever or whoever, over some period of time, experiences a life like ours. My main interlocutors’ (e.g., Burkhardt's, David Shoemaker's) answer: in virtue of something else, i.e., one's being psychologically continuous with (or connected to) an experiencer of a life like ours.

But there is also an important sense in which my discussion is distinct from the discussion over the question of what matters in survival. My answer to the question of what matters in possession – along with, accordingly, my analysis of Marquis's argument – does not require me to take a stance on the answer to what matters in survival. We can see this by returning to the debate between endurantists and perdurantists. In the literature on what matters in survival, it has been argued that endurantism implies the identity answer to what matters in survival, whereas perdurantism opens up the possibility for alternative answers.Footnote ³⁰ Moreover, many proponents of the view that psychological continuity (or connectedness) is what matters argue for this position in part by appealing to perdurantism or to a view that arguably implies it.Footnote ³¹ But, if my arguments above are sound, then both endurantists and perdurantists should answer the question of what matters in possession as I have. That is, they should endorse Possession (and, accordingly, Deprivation). So, even if the dispute between endurantists and perdurantists leaves open how to answer the question of what matters in survival, the question of what matters in possession (and, accordingly, in deprivation) is clear: identity matters.Footnote ³²