Bodies and Their Parts

Robert Francescotti

doi:10.3390/philosophies10060134

Department of Philosophy, San Diego State University, San Diego, CA 92182, USA

Philosophies2025, 10(6), 134;https://doi.org/10.3390/philosophies10060134
(registering DOI)

This article belongs to the Special Issue Mereology in Metaphysics, Science and Logic

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Abstract

Here I develop an account of what makes something a part of the body. The account presented is not an analysis of parthood generally, but an analysis of parthood specifically for what we are inclined to call a “body,” including but not limited to the bodies of human and nonhuman organisms. Drawing on influential accounts of parthood in the philosophical literature, with an emphasis on the core idea that something is a part in virtue of its contribution to the whole, I develop an analysis of bodily parthood that identifies what contribution to a body is necessary and sufficient for being a part of that body.

Keywords:

the body; our bodies; parts; wholes; bodily parthood

1. Introduction

Drawing on some influential accounts of parthood in the philosophical literature, I develop an analysis of what makes something a part of the body. This is not an analysis of parthood generally but an account of parthood specifically for things that we are inclined to call a “body,” including but not limited to the bodies of humans and the bodies of non-human organisms. The account developed here remains neutral on whether temporal parts count as genuine parts of objects. I am concerned here with the spatial parts of a body rather than its temporal parts; more specifically, I aim to identify what it is for something in the spatial vicinity of a body at a certain time to count as a part of that body, a genuine body part, at that time.

Developing an account of bodily parthood provides some insight into the more general issue of what makes one material object a part of another. In addition to offering some insight regarding material composition generally, the analysis provided here also serves to alleviate worries some philosophers have regarding the notion of the body. Some authors, including Peter van Inwagen [1], Eric Olson [2] (pp. 143–153), Douglas Long [3], and Jay Rosenberg [4] (chs. 2 and 3), have argued that the notion of the human body and the notion of a body in general, as used in philosophical discussions of the relation between a person or mind and the corresponding body, is conceptually confused and even unintelligible.1 Two concerns, among others, have been expressed: (i) that talk of the body is problematic and (ii) that talk of a body being one’s own body (x’s body as opposed to y’s body) is problematic. By offering a successful account of what makes something a part of a body, we can show that at least (i) is false; a successful account of bodily parthood will reveal exactly what a body is, i.e., the aggregate of those parts the account tells us it has.

If the notion of the body is intelligible, then so are various questions regarding how we relate to our bodies (e.g., whether we are identical with our bodies, whether we are constituted by them, or whether they are proper parts of us). Knowing what makes something a part of a body might be of some help in answering these questions. For example, if we decided that there are things that count as parts of our bodies that should not be considered parts of us, that would seem reason to deny that we are identical with our bodies. Also, on the assumption that at least many of the parts of our bodies count as parts of us, an account of bodily parthood can help us decide which items within the spatial boundaries of our bodies (e.g., a pacemaker, a brain implant, or a fetus) count as parts of us.

So it is desirable, for various reasons, to develop a successful account of bodily parthood, which is what I aim to do here. With the help of the accounts of parthood discussed in Section 2 and Section 3, and with emphasis on the idea that something is a part in virtue of its contribution to the whole, I present an account of bodily parthood in Section 4. The account specifies what contribution to a body is necessary and sufficient for being a part of that body. Some potential objections to my account are answered in Section 5.

2. Caught Up in a Life

What van Inwagen [11,12] called the “Special Composition Question” is the question of what conditions are necessary and sufficient for a plurality of material objects, the xs, to compose some object y. One extreme answer to this question is the mereological universalist answer that the x’s always compose a y; i.e., whenever there is more than one x, there is a composite y that they form. This is an extreme answer since it entails that there exist so many things we are inclined to believe do not exist, including a material object that is composed of exactly my left thumb, Madison Square Garden, the planet Venus, and the lower half of the tallest giraffe. Another extreme answer is the mereological nihilist answer that composition never occurs; there are no composite material objects, only simples. Van Inwagen’s answer to the special composition question lies between these extremes. According to van Inwagen, the xs compose something “if and only if the activity of the xs constitutes a life (or there is only one of the xs)” [12] (p. 82). While lying between the two extremes, this answer is far closer to nihilism than many would like, for it entails that the only material objects that exist are either simples or things with life; and assuming that the only things with lives, i.e., biological lives, are organisms, then for van Inwagen the only composite material objects that exist are organisms.2 Most of us are inclined to think that there are (that there exist) many non-simple proper parts of organisms, along with all the non-simple non-organisms the sciences mention and many of the non-living objects of ordinary discourse, including human artifacts, and all of their widely recognized non-simple proper parts.

Van Inwagen points out that his answer to the special composition question together with the claim that things that have lives are organisms entails that “x is a proper part of y if and only if y is an organism and x is caught up in the life of y” [12] (p. 94), which entails that the only things with proper parts are organisms. However, one need not endorse van Inwagen’s implausible answer to the parthood question to believe that, at least where organisms are concerned, the parts are all and only those things suitably caught up in the life, i.e., the biological life, of the organism. On this view, if something does not suitably participate in the biological life of the organism, it does not count as a part of the organism. Olson, for example, claims that a pacemaker or stainless-steel hip is not a part of one’s body for the same reason a dialysis machine to which one is attached is not a part of one’s body: it is not caught up in the body’s metabolism, it does not repair itself by healing and forming scar tissue, it doesn’t assimilate nutrients from the bloodstream, etc. [2] (p. 135). David Hershenov, likewise, claims that “the reason we should not consider pacemakers or dirt clumps part of the body is that they do not biologically participate in the life of the organism—growing, scarring, dying, healing, and so on” [7] (p. 48).3

Let’s give the label ‘the Life Account’ to the view that x is a part of (the body of) y, for any organism y, if and only if x is caught up in the life processes of y (and x is a proper part of y iff that is the case and x ≠ y). One can accept the Life Account while believing that there are many material composite objects that are not organisms, and one can accept the account while believing that organisms can have complex proper parts that are not organisms themselves. Still, it seems to me, the Life Account is too strong. It seems that there are parts of organisms, i.e., parts of their bodies, that are not involved in the organism’s life processes in any significant way. Body parts can include clumps of dead cells, which are not involved in the organism’s metabolic processes or other life functions.4 Also, it is not clear to me that pacemakers and stainless-steel hips cannot qualify as parts of one’s body. In fact, with the analysis of bodily parthood I offer in Section 4, a strong case can be made, as shown there, that these do count as parts of one’s body. Moreover, I prefer an account of what it is to be a body part that applies to cases in which the individual has a body and the body has parts, but the individual does not have a biological life, as in the case of corpses or any inorganic material persons there might be. These individuals have what we call “bodies,” and I presume that what makes something a part of those bodies is also what makes something a part of non-living bodies; this seems especially true in the case of the corpse since it seems that the corpse is the same body as the body that was once alive.5

3. Contributing to the Characteristic Behavior of the Whole

Hugh Mellor [19] (p. 68) characterizes the components of our bodies as “working parts,” whose causal interconnections contribute to the body’s causal unity. Similarly, Carl Gillett describes scientific constituents as “working parts because the ‘work’ of these integrated teams of individuals does, or would, together implement the ‘work’ of the relevant whole that they constitute” [20] (pp. 318–319).6 As Gillett mentions, “an individual is a part of another, in the sense used in compositional models/explanations, when the individual’s properties or activities realize or implement properties or activities of the relevant whole” [22] (p. 256).

Let us focus on the idea that something’s being a part depends on the contribution it makes to the activities of the whole. In the case of organisms, some of the work the parts do is contributing to the life of the whole (including being “caught up in” that life). However, even in the case of organisms, parts contribute to activities of the whole other than life processes. And a plausible suggestion is that some significant contribution of the parts to activities of the whole, in terms of life processes or otherwise, is what makes something a part of a body both in the case of organisms and non-organisms.7 To see how the details of such an account should go, I will focus on Marie Kaiser’s [15,16] account of parthood for biological individuals. I am concerned with giving an account of bodily parthood, and the term ‘biological individual’ includes more and less than what ‘body’ includes—more because it includes, for example, “gene regulatory networks, immune systems, certain populations, and certain ecosystems” [16] (p. 74) and less by not including non-biological bodies, e.g., the bodies of inorganic intelligent machines. However, since the account Kaiser offers is a good start at analyzing parthood generally, let us focus on her analysis for a bit and see what modifications are required to yield an adequate account of bodily parthood.

Kaiser points out that spatial inclusion is not sufficient for biological parthood; “if a doctor leaves a cotton ball inside of my stomach during surgery we would not say that the cotton ball became a part of me just because it is spatially located inside of me” [16] (pp. 70–71).8 So besides a requirement of spatial inclusion, Kaiser adds a compositional relevance condition.

An object x, which engages in biological process p, is a biological part of an object y, which shows characteristic behaviors b₁,…b_n, if and only if
Substantial spatial inclusion (SSI): x must be spatially located inside or in the region that the natural boundary occupies if y has a natural boundary and
Compositional Relevance (CR): p is relevant to at least one of b₁,…b_n; that is, p makes a necessary contribution to a condition that is minimally sufficient to one or more of b₁,…b_n.9 ([16] (p. 81))

Condition 2 requires that the part makes a necessary contribution to a condition that is minimally sufficient for one of the characteristic behaviors of the whole. Kaiser [16] (p. 80) mentions that her inspiration for this way of putting it is J. L. Mackie’s [25] claim that we should understand a cause as an INUS-condition, i.e., as insufficient for the effect, but as a necessary part of a set of conditions that is unnecessary but sufficient for the effect. Describing the contribution of the part as a necessary contribution to a sufficient condition allows for “redundant parts.” Kaiser mentions, for example, that each of the kidneys is a part of the organism by making a contribution that is not itself necessary (since it is not necessary for survival that both kidneys filter blood), but is a necessary contribution to the functioning of the pair, which is sufficient for the filtering of blood. The notion of a necessary contribution to a condition that is minimally sufficient also allows for parts that are only collectively contributory, “e.g., the calcium ions in a muscle fiber that only collectively have a significant effect on muscle contraction” [16] (p. 80). However, it is important to bear in mind that while Mackie introduces the idea of INUS-conditions in an account of causation, the part-whole relation is synchronic. The contribution mentioned in Kaiser’s condition 2 is to be understood as a contribution at the time that the parts are making to the behavior of the whole at that time.10 To make this clearer, we might include temporal indices, e.g., the parts at t contributing to the characteristic behavior of the whole at t, to highlight that the contribution of the parts to the whole that’s being mentioned is constitutive and not causal.11 (Or we might add a temporal inclusion requirement alongside the spatial inclusion and compositional relevance requirements, as Kaiser [15] (pp. 177–181) does.)

Kaiser’s account, as mentioned, applies to biological individuals. But suppose we utilize it as an account of what makes something a part of a body, biological or not, by replacing ‘object y’ with ‘body y’ and eliminating the word ‘biological’. That would be a promising account of bodily parthood, but it would not be good enough. For an acceptable account of bodily parthood, some significant modifications are required.

Condition 1 makes reference to the part being within the natural boundary of the whole, where natural boundaries “typically are identified by their function as selective barriers and by the material discontinuities or structural differences that they involve” [16] (p. 72). The ‘if’ in condition 1 (‘if y has a natural boundary’) allows that some biological individuals with parts need not have a natural boundary, “such as gene regulatory networks, immune systems, certain populations, and certain ecosystems” (p. 74). However, in an analysis of bodily parthood, I believe that the spatial inclusion requirement need not be conditional, since what we would call “a body” or “one’s body” is not as spatially scattered as those items are. Also, I believe there is no need to reference natural boundaries (i.e., in an account of bodily parthood). Kaiser worries that a “primitive spatial inclusion” requirement, which merely requires spatial containment, runs the risk of being circular. Item x being spatially included in y amounts to x being located within the spatial boundary of y. However, if we characterize the spatial boundary of an object as that which contains all of its parts, then “whether x is a biological part of y would depend on whether x is spatially included inside the boundary around y and y’s other parts. In other words, the individuation of one part of a whole would presuppose having individuated all of its parts” [16] (p. 71). But it is not true that knowing whether x lies within the spatial boundary of y requires already knowing all of y’s parts or even whether x is a part of y. Something can be within the spatial boundary of one’s body without being part of that body. So we can know that something lies within the spatial boundary of one’s body without knowing whether it is a part of that body, and definitely without having decided whether any of the other things in that spatial boundary (e.g., a pacemaker, a steel-hip or a fetus) count as parts of that body. So, it seems, the analysis would not be circular if we replaced Kaiser’s “substantial spatial inclusion” condition 1 with a simple spatial inclusion requirement.

There is another change needed for Kaiser’s account to apply to bodily parthood (and I think it is needed even for an account of biological parthood). There is emphasis in the analysis on contribution to characteristic behaviors of the whole, and Kaiser justifies the reference to characteristic behaviors by noting that “Plausibly, not any arbitrary process of the whole should determine what its parts are because the whole might be involved in some processes only accidentally or exceptionally” [16] (p. 75). But why suppose that a part cannot be something that an object has accidentally or exceptionally? Kaiser mentions that her account is singularist, where on “a singularist account of biological parthood, part-whole relations exist between individual biological objects, and claims about kinds of biological part-whole relations are generalizations that arise from investigating particular part-whole relations” [16] (p. 68). An account that tells us, for example, that humans, in general, have tonsils as parts is not a singularist account. On a singularist account of parthood, whether x is a part of y depends solely on the condition of x and y themselves, independently of what parthood relations exist in other objects—independently of whether other items of the kind to which y belongs (other humans, for example) have as parts items of the kind (e.g., tonsil) to which x belongs.12 Now, we should expect from a singularist account that something might be of a certain kind while having a part that isn’t typical of members of that kind, as Kaiser acknowledges; “Viruses are surely not among the parts that cells have, in general. But they may be parts of a subtype of cells, namely infected host cells” [16] (p. 68). However, it seems it might also be true that y having x as a part is not only atypical of some general kind to which y belongs, but atypical of y itself and not contributing to any behavior that is characteristic even of y.

In his analysis of “corporeal composition,” one of the necessary conditions Stuart Glennan [26] lists is that the parts contribute to some of the composite’s “characteristic behaviors and capacities.” And regarding the characteristic qualification, Glennan warns

Since corporeal composition is a relation between particulars, each composite S will have a unique set of components, and these components may be of kinds that do not belong to all individuals of kinds of which S is an instance. […] Moreover, some components may be unique to a particular instance—truly “one of a kind.” Suppose a particular cell S becomes infected with a virus that is rarely found in cells like S; that virus will still be (at that time) a component of S, because it alters the characteristic capacities and behaviors of that particular cell. [26] (p. 11447)

As Glennan indicates, when cell S becomes infected with the virus, S acquires that virus as a part, even though that virus is not characteristic of the kind of cell to which S belongs. But suppose, also, that immediately after cell S becomes infected, S dies. During the brief moment the virus is a part of S, it might alter, momentarily, the behavior and capacities of S. But assuming the moment is very brief, e.g., only an instant, it seems the new behavior/capacities would not count as characteristic of S. If we were not offering a singularist account of parthood, if we were providing conditions for what makes something generally a part of items of a certain kind, then citing characteristic behavior is in order, but with a singularist account it seems it is not. As the infected cell example shows, x can be a part of y at a certain time by making a contribution to the behavior and capacities of y at that time, even if that behavior and those capacities are not characteristic of y at that time or any time.

By eliminating reference to characteristic behavior, we might be able to handle a certain type of case that Kaiser recognizes as potentially problematic for her account. One of the “hard” cases for an account of biological parthood that Kaiser considers is the case of “irrelevant” parts, parts that “engage in processes that are irrelevant to any characteristic behavior of the whole (e.g., because they have become nonfunctional during evolutionary history)” [16] (p. 82). Kaiser mentions that “our appendix does not engage in processes that are INUS-conditions for one of our characteristic behaviors, such as our survival, reproduction, reasoning, or cooperation with others, but we typically consider our appendix to be a biological part of us” [16] (p. 83).13 Glennan’s [26] account of “corporeal composition” requires that the components contribute to some of the composite’s characteristic behaviors or capacities (‘CBCs’, as Glennan labels them).14 And in response to concerns about irrelevant vestigial parts, Glennan mentions that “appendices did do something in the past, and they likely still have some effects on humans. In fact, there are now suggestions that the appendix retains a function (most likely sequestering bacteria)” [26] (p. 11457). However, even though appendices did something in the past, the question for any account that requires contribution to CBCs is whether x contributes at t to the CBCs of the composite at t; also, while the appendix might now contribute to some of our CBCs, it would still count as a part of us even if it did not have any such effects.

Glennan does mention, in the last quoted passage, that appendices “likely still have some effects.” Suppose we drop the requirement that the effects are characteristic behavior or capacities. Then perhaps we can acknowledge that the appendix is a part of one’s body even if it doesn’t contribute to any characteristic behavior or capacities of the body. Also, by not focusing only on characteristic effects, we can allow that a newly acquired item (e.g., a virus) can qualify as a part (of the cell and the whole body that contains that cell) by contributing to uncharacteristic behavior or capacities of the whole.

So, for an account of bodily parthood, in addition to modifying Kaiser’s spatial inclusion requirement (to make it non-conditional and without reference to natural boundaries), let us revise condition 2 and require that the part contributes to some features of the whole, characteristic or otherwise.

4. Involvement in (the Instantiation of) Properties of the Whole

In addition to “irrelevant parts”, Kaiser [16] (pp. 81–82) includes in the list of potential problem cases “inactive parts” which only potentially contribute to characteristic behavior of the whole. By emphasizing the contribution of the parts to characteristic behavior or capacities, Glennan’s analysis allows that something inactive can be a genuine part, with unexercised capacities contributing to unexercised capacities of the whole [26] (p. 11457). So let us retain the idea that the contribution to the whole that makes something a part can be a contribution to the whole’s capacities and not just to its actual behavior. Also, rather than referencing “behaviors” and “capacities,” suppose we talk about the contribution of the parts to properties of the whole, where properties include, among much else, actual behavior and capacities. And, as mentioned in Section 3, to more effectively handle “irrelevant” parts, let us delete reference to characteristic features. An “irrelevant” part that does not contribute to characteristic behavior or capacities might still be relevant, and therefore qualify as a part, by contributing to properties of the whole even if those properties are uncharacteristic. In addition, suppose we use time indices, as Glennan [26] does (and see Kaiser’s temporal inclusion condition [15] (pp. 177–181)), to make it clear that the contribution of the part to the whole is synchronic.

Glennan’s analysis does not include a spatial inclusion or containment requirement since the “bodies” covered by his use of the term ‘corporeal’ include highly spatially scattered items, such as populations, ecosystems, and galaxies [26] (p. 11441). For a highly spatially distributed composite, Glennan notes, there is no spatial region that its parts must fall within (“unless we define the region of the composite S analytically as the union of the regions of its components X_i, in which case the requirement of containment becomes trivial” [26] (p. 11449)). However, there is a spatial boundary to what we would normally call a “body”—such as the body of a live human or nonhuman animal, or the body of a corpse. So let us add a spatial containment requirement and make it nonconditional (unlike Kaiser’s spatial inclusion condition, which is meant to apply to biological individuals generally, some of which do not have the natural boundaries she describes).

As an initial attempt, consider:

Necessarily, x is a part of body y at time t if and only if
x is contained at t within the spatial boundary of y, and
x is involved at t in the instantiation of at least one of y’s properties; i.e., x’s presence at t is among that in which the instantiation of at least one of y’s properties consists.

This account is neutral on whether temporal parts count as genuine parts of objects. The account is not concerned with characterizing temporal parthood. It, instead, specifies what it takes for something within the spatial vicinity of a body at a certain time to count as a genuine part of that body at that time.

The analysis states as a necessary condition for being a part of the body that the part is involved in the instantiation of at least one of the body’s properties. ‘At least one’ allows for all. In the case where x is the improper part of body y, i.e., where x = y, x is trivially involved in the instantiation of all of y’s properties. Also, while most of the examples of body parts given so far are those we are inclined to call “objects”, e.g., stomach, appendix, cell, as Ingo Brigandt [28] argues, functions (as activities) are bodily parts just like structures are. So I think the xs that can qualify as parts should include activities, and also events generally, and regions of space, and other non-objects. Note, moreover, that being within the spatial boundary, as required by condition 1, includes being at the very boundary, part of the periphery (as Kaiser puts it, “spatially located inside or in the region” that the boundary of y occupies [16] (p. 73)).

I mention x’s being “involved” in the instantiation of y’s properties. This is a convenient way of saying, as indicated, that x is among the objects, activities, processes, etc., in which the instantiation of y’s properties consists. We might also express this basic idea in terms of realization, as Gillett does, by characterizing parts as having properties that realize properties of the whole [20,21,22] (ch. 2 of [21]). Apart from the controversy regarding what realization amounts to, I prefer my way of expressing the basic idea since I find that the problems with the initial attempt above, which are just about to be revealed, are more easily solved with talk of involvement in the instantiation of the body’s properties. (As mentioned in Section 5, there is another significant way in which my analysis of parthood differs from Gillett’s account.)15

While it is a start, the initial attempt I presented certainly will not do as it stands, since conditions 1 and 2 are clearly not jointly sufficient for being a part of a body. Consider the relational property of being three meters from a boulder. The instantiation of this property consists partly in the presence of a boulder, but the boulder is not a part of any body that is three meters away from it. We avoid the result that the boulder is a part of the nearby body with spatial containment condition 1. However, the instantiation of some of the body’s relational properties can also consist in relations that the body bears to non-parts that are within its spatial boundary. Recall the example of the cotton ball accidentally left inside the patient’s body during surgery. The cotton ball is within the spatial boundary of the body, and it is involved in that body’s instantiation of the property containing a cotton ball; i.e., the presence of the cotton ball is among that in which the instantiation of that property consists. Still, the cotton ball, it seems, is not a part of that body. (And focusing on contribution to characteristic features doesn’t solve the problem, for if the cotton ball had remained inside the person long enough, containing a cotton ball arguably would have become a characteristic feature of that person’s body, but the cotton ball would not thereby have become a part of the person’s body.)

To get the apparently correct result that the cotton ball is not a part of the body, I propose rephrasing condition 2 as follows:

2.: x is involved at t in y’s contribution to the instantiation of at least one of y’s properties; i.e., x’s presence at t is among that in which y’s contribution to the instantiation of at least one of y’s properties consists.

While the cotton ball is involved in the body’s instantiation of the property of containing a cotton ball, it is not involved in the contribution the body makes to the instantiation of that property. However, the stomach containing the cotton ball is involved in the contribution the body makes to the instantiation of at least some of the body’s properties, e.g., many of its digestive properties. The stomach is also involved in the contribution the body makes to the body’s mass and weight, since obviously the stomach contributes to the mass and therefore the weight of the body. But this is not true of the cotton ball; the presence of the cotton ball does not itself render the body more massive.

What about the functioning pacemaker? Is it a part of the person’s body? I mentioned, in Section 2, that Olson and Hershenov claim that the pacemaker is not a part of the body. However, on my account, a strong case can be made that it is a body part. The pacemaker obviously contributes to the circulatory activities of the body. Of course, external items can also affect circulatory activity. And the fact that the pacemaker is an internal contributor does not entail that it is a part of the body; a cotton ball suitably situated might contribute to the body’s circulatory activity. It is the way in which the functioning pacemaker contributes to the body’s circulatory processes that makes it compelling to regard it as a part of the body. The pacemaker is involved in those circulatory processes themselves. The circulatory activity itself consists of, among much else, the presence of the pacemaker and its functioning. Since those activities are among the ways in which the body contributes to the instantiation of its circulatory properties, it does seem that the pacemaker is a participant in the body’s contribution to the instantiation of those properties. The fact that the pacemaker does not assimilate nutrients from the bloodstream, is not caught up in one’s metabolism, and does not heal and form scar tissue (as Olson [2] (p. 135) and Hershenov [7] (p. 48) remark) does not make it any less involved in the body’s contribution to its circulatory processes. Those activities are vital processes. But note that being involved in a vital process is not necessary for being a part of the body, on my account. One would not subtract the weight of the pacemaker when measuring the person’s weight, suggesting the pacemaker is included in the body’s contribution to the weight recorded, which makes it a part of the body on my account even though the instantiation of that weight is not itself a vital process.

The same seems to me to also apply to the stainless-steel hip that Olson claims is not a part of the body. It is plausible to consider it, too, as being involved in the body’s contribution to the weight recorded. And the very ambulatory activity in which the artificial hip participates is arguably activity of the body itself, which makes it plausible to view the presence of the artificial hip as included in the body’s own contribution to the instantiation of its properties. However, as Olson mentions, “We cannot add parts to an animal by implanting rocks into its abdominal cavity” [2] (p. 135). That’s correct, but not because the rocks are inorganic or not caught up in one’s metabolism, but because the rocks are not involved in the body’s contribution to its properties, e.g., not involved in the body’s contribution to its circulatory activity, its digestive activity, or even its mass.

One more condition needs to be added to the analysis, for even with the rephrasing of 2, the conditions so far are not jointly sufficient for bodily parthood. Consider something x that uncontroversially is a part of y. Now consider the sum of x and some other internal item, z, that we would want to say is not a part of y. Suppose, for example, that x is the stomach, z is the cotton ball contained within, and y is the body of the person with that stomach. Given that both x and z are within the spatial boundary of y, the combination x + z is within that spatial boundary. Also, assuming that x meets the new condition 2, so does x + z; e.g., the combination of the stomach and the cotton ball within is involved, by virtue of the stomach being involved, in the body’s contribution to the instantiation of some of its properties. So, even with the revised condition 2, the analysis yields the implausible result that the combination of x and z (e.g., stomach + cotton ball) is itself a part of body y.

Recall that Kaiser requires that the part is engaged in a process that makes “a necessary contribution to a condition that is minimally sufficient” for one or more of the whole’s characteristic behaviors. One might think that introducing a minimally sufficient qualification to my analysis can solve the stomach + cotton ball problem. Perhaps it can, but not without introducing other problems. Neither the stomach itself nor any of the individual processes the stomach undergoes is sufficient, and therefore not minimally sufficient, for its involvement in the body’s contribution to its properties. Various relations to other parts of the body are necessary for the stomach’s involvement in the body’s contribution to its properties. Even the stomach’s involvement in the body’s contribution to its mass requires that the stomach is located within the periphery of the body. So if we require that the contribution of the part is minimally sufficient (for being involved in the body’s contribution to the instantiation of its properties), we risk the unacceptable result that the stomach is not a part of the body. So I prefer a different way to avoid the result that the combination of stomach + cotton ball is a part of the body.16

Let us add a third condition requiring that for any combination of items, if the combination is a part of the body, then each of the items satisfies condition 2.

Bodily Parthood:
Necessarily, x is a part of body y at time t if and only if
x is contained at t within the spatial boundary of y,
x is involved at t in y’s contribution to the instantiation of at least one of y’s properties; i.e., x’s presence at t is among that in which y’s contribution to the instantiation of at least one of y’s properties consists, and
if x is a combination of x₁,…x_n, then each of x₁,…x_n satisfies condition 2.

The mention of a combination utilized in condition 3 does not presuppose bodily parthood. It might be that x is the combination of x₁,…x_n without x qualifying as anyone’s body or even what we would call a “body”; x might be the combination of a heart and a left index finger. It might also be that x₁,…x_n are not parts of any body; x₁,…x_n might be a collection of molecules in the atmosphere, each spatially very distant from each of the others, and not comprising anything we would call a “body.” We can, therefore, know that x is a combination of x₁,…x_n without knowing that bodily parthood is involved, and, indeed, while knowing that bodily parthood is not involved. So condition 3 does not presuppose the notion of parthood that is being analyzed, which is bodily parthood. So there is no threat of circularity.

However, one might wonder whether condition 2, with the mention of involvement in the body’s contribution to the instantiation of its properties, introduces some kind of unacceptable circularity. This worry will be addressed in Section 5, along with other objections. But before considering possible objections, let’s review some of the main details of the account along with its merits. By eliminating reference to characteristic behavior, the account allows for parts that contribute only to uncharacteristic behavior of the whole, e.g., bone spurs forming, causing a loss of mobility that is uncharacteristic of the person. Also, by not emphasizing characteristic behavior and referencing properties in general, the account allows for what Kaiser calls “irrelevant parts.” As mentioned earlier, Kaiser notes that the human appendix “does not engage in processes that are INUS-conditions for one of our characteristic behaviors, such as our survival, reproduction, reasoning, or cooperation with others” [16] (p. 83). Even if the appendix does not contribute to those characteristic behaviors, it does contribute to the body’s having some of the properties it has, including its mass. By being involved in the body’s contribution to its mass, the appendix qualifies, on my account, as a part of the body.

Also, by referencing contribution to the whole’s properties and not just actual behavior, the account allows for “inactive parts,” parts that merely have the disposition to contribute to the behavior of the whole. Kaiser recognized inactive parts as problematic for her analysis. Since the properties of the whole include not just actual behavior but also capacities, which Glennan’s account mentions, my analysis allows that parts can be inactive but still count as parts by being involved in the body’s contribution to the instantiation of some of its properties.

Reference to involvement in body y’s contribution to the instantiation of some of its properties was a needed addition. Consider anything x within the spatial boundary of a body that seems not to be a part of that body (such as the cotton ball left behind during surgery, or the morsel of food just placed in one’s mouth, or a splinter under the skin). Item x is involved in the instantiation of at least one of the body’s properties, e.g., the property of containing x. However, assuming that x is not involved in the body’s contribution to the instantiation of that property, or any other of the body’s properties, then according to the revised condition 2, x is not a part of that body. However, if x is a part of the body, then it is involved in the body’s contribution to the instantiation of at least some of the body’s properties. For instance, unlike the morsel of food just placed within, the mouth is among that in which the body’s contribution to the instantiation of many of its properties consists, including food intake, digestion, respiration, and speech production.

As mentioned earlier, Glennan does not include a spatial containment requirement since the “bodies” covered by his use of the term ‘corporeal’ include highly spatially scattered items, such as populations, ecosystems, and galaxies. However, there is a spatial boundary to what we would normally call a body—such as the body of a live human or nonhuman animal, or the body of a corpse. For this reason, condition 1 is included. Also, the inclusion of condition 3 seems necessary. Whatever contribution part x makes to the properties of body y (e.g., by being involved in y’s contribution to the instantiation of its properties), there is the worry that the combination of x plus some other internal item that is not a part of y might also make that contribution to y’s properties (e.g., might also be involved in y’s contribution to the instantiation of its properties). Condition 3 prevents the combination itself from being classified as a part of y.

It should also be noted that the account of bodily parthood provided here is compatible with a variety of different views regarding how we relate to our bodies. One can certainly accept the account while also believing that we, human persons, are identical with our bodies (thereby accepting my analysis of bodily parthood as also revealing what makes something a part of us). However, accepting the account of bodily parthood offered here certainly does not require believing that we are our bodies. Consider the constitution view that we are physically realized individuals who are wholly spatially coincident with our bodies but not identical with those bodies.17 A constitution theorist can accept my account of what makes something a part of the body (and then decide whether all of our body parts are parts of us, which would be a further issue).

There is also the view that has been called “compound dualism,” according to which, each of us is comprised of two fundamentally different components: a physical body and an immaterial mind/soul.18 And there is pure dualism, according to which we are purely immaterial minds/souls, the associated physical body not being a part of us.19 Proponents of either of these two versions of substance dualism can accept my account of bodily parthood. And my account gives the correct result that if either of those two views is correct, then the immaterial mind is not a part of the body, and it is not a part of the body, according to those views, for two reasons: it is not contained within the spatial boundary of the body on either of those versions of substance dualism, and on either version, even if the body is causally affected by the immaterial mind, the latter is not involved in the body’s contribution to the instantiation of the body’s properties.

There is also the theory that we are identical with our brains, or some suitably functioning part of the brain.20 This view is consistent with the account of bodily parthood offered here; indeed, if the view that we are our brains (or parts of it) is correct, then we ourselves would be body parts (proper parts of the containing body), and we would count as body parts on my analysis if that view were correct.

I take it to be a merit of my account that it is neutral regarding these different views, open to a proponent of any of them. (However, I also leave open that my account might help us decide which of those theories, or others, to accept or reject. For example, if we discover that there is at least one thing that is most plausibly considered a part of our bodies, on my account, but which should not be considered a part of us, that might be some reason to deny that we are identical with our bodies. Or if we decide that there is at least one thing that is a body part, according to my account, which also intuitively counts as a genuine part of us, that might provide some reason to deny pure dualism. These are just a couple examples of how my account of bodily parthood might bear on the truth/falsity of the different views mentioned above regarding how we relate to our bodies.)

5. Some Objections Answered

I mentioned the notion of a working part as described, for example, by Mellor and Gillett. That notion implies not only that the parts work to implement the properties of the whole, but also that they work together to do so, as “integrated teams of individuals” (Gillett [20] (p. 318)). In his analysis of parthood, Gillett requires not only that properties of the parts realize properties of the whole, but also that many of the parts bear “powerful and/or productive relations to each other” [20] (p. 323), parts productively interacting with other parts [22]. And in his account of corporeal composition, Glennan requires that a part contributes to some characteristic behaviors and capacities of the whole, not by itself, but “jointly” with at least some other parts, and that those parts “exhibit cohesion with each other during the life of the composite” [26] (p. 11446). This idea that the parts work together in some significant manner and to a significant degree is absent from my analysis, and one might find that problematic.

The parts of a composite generally do interact to a large degree to yield the properties of the whole. It is not necessary, of course, that a part of a body engage in significant interaction with every other part of the body. But it seems it is not even necessary for a body part to significantly interact with any other parts of the body. Perhaps the appendix does perform some function, as Glennan mentions, but even if this activity were quite minimal, the appendix would still count as a part of our bodies. And even if there were no significant interaction between the appendix and any other parts of the body, the appendix would still be a part of the body. Suppose that blood flow to the appendix were stopped and it became a collection of dead cells. Then there would be very little interaction between it and other parts of the body, no more interaction with other parts of the body than there would be between the cotton ball left behind and the stomach that contains it. Yet, it seems the appendix would still count as a part of the body.21^,22

One might argue that a type of interaction that is necessary for parthood is the sort of interaction described by “bound state” accounts of composition and parthood. As an answer to van Inwagen’s special composition question, Jonas Waechter and James Ladyman propose that “in order to compose something at t₀, physical objects must form at t₀ a connected plurality under the relation of forming a bound state. In a slogan, objects compose something at t₀ iff they form a chain of bound states at t₀” [41] (p. 109). Likewise, Kerry McKenzie and F.A. Muller propose that “physical objects form a composite object iff these physical objects interact and are in a common bound state” [42] (p. 234). A bound state is defined in terms of the relation between potential and kinetic energy. As McKenzie and Muller explain, a bound state “by definition is a state in which the objects have a total energy that is negative (E < 0). In that case, the potential energy of the composing objects (which is always <0) is larger in absolute value than their kinetic energy (which is always ≥0)” [42] (p. 234). What is attractive about the bound state answer to the special composition question is that it is highly scientifically informed while giving the plausible result that composites include not only organisms, but many of the other composite items recognized by science and common sense. Julian Husmann and Paul Näger note that “what all these composite objects seem to have in common is that their parts somehow bind to each other: Nuclei bind to electrons to form atoms, atoms bind to form molecules, molecules bind to form cell membranes and so on” [43] (p. 72).23

My analysis does not mention anything about parts of a body being in a common bound state (or forming “a chain of bound states,” as Waechter and Ladyman [41] describe it) and one might think this is a problem with my account. While it seems plausible that many of the parts of a composite are generally in a common bound state, that does not seem to be a necessary condition for parthood. As a worry for the bound state account, McKenzie and Muller [42] (p. 240) mention the concern, expressed by Paul Teller, that the jacket and trousers of a suit fail to be in a bound state, but they do seem to be parts of the suit.24 Claudio Calosi adds that bikinis, the many-volume Encyclopedia Britannica, a tea service, and a deck of poker cards implausibly do not exist on the bound state answer to the special composition question since the parts are not in a bound state [44] (p. 492). Not only do the composites Calosi mentions seem to exist, but also what we would consider the parts of these composites are not in a bound state with the other parts. So it seems that being in a common bound state is not necessary for being parts of a composite.

It might be insisted that where bodies are concerned, like our bodies or the bodies of other organisms, the parts need to be in a bound state. However, it is not clear why that must be the case. It is certainly not part of the very notion of a body that each of the parts must be in a common bound state, especially when being in a bound state is defined in terms of the relation between potential and kinetic energy. And it is not clear why being in a bound state with other parts is even non-analytically necessary for something to be a part of a body. Until it is shown that an item can meet each of the conditions of my analysis and still not be a part of the body because it is not in a common bound state with the other parts, I am reluctant to include a bound state requirement.25

Another type of objection to my analysis regards circularity. As mentioned in Section 3, contrary to what Kaiser suggests, a basic spatial inclusion requirement does not make an analysis of parthood circular. Since some things within the spatial boundary of a body are not parts of the body, we can know that x lies within the spatial boundary of some body y without knowing whether x is a part of y. So the notion of spatial containment in condition 1 of the analysis proposed here does not presuppose bodily parthood.

Condition 3 might raise circularity concerns. I required that “if x is a combination of x₁,…x_n, then each of x₁,…x_n satisfies condition 2” to handle the worry that if an internal part x of body y satisfies condition 2, then so will x + z, where z is an internal item that is clearly not a part of y. And given that x + z also satisfies condition 1, without condition 3 the result is that x + z is a part of y when intuitively it is not, given that z is not a part of y. If x is the combination of x₁,…x_n, then in some sense each of x₁,…x_n are parts of x. However, as mentioned in Section 4, x’s being a combination of x₁,…x_n does not entail that x₁,…x_n are bodily parts of x. It might be that x is not what we would call a “body,” and it might be that x₁,…x_n are not parts of any body; x might be the union of the cotton ball left in one’s stomach, a splinter under the skin, and the undissolved pill one just placed on one’s tongue (which seem to me not to be parts of the body). So condition 3 does not presuppose the notion of parthood, bodily parthood, that is being analyzed.

There is another potential circularity concern, regarding condition 2. Item x being involved in the instantiation of some of y’s properties does not require that x is a part of y, since items external to y can be involved in the instantiation of y’s properties, especially when those properties are relations to external items (e.g., being three meters from a boulder). That is why I required involvement in the body’s contribution to the instantiation of its properties. One might suspect, however, that x’s being involved in the body’s contribution to the instantiation of its properties presupposes that x is a part of that body. But that is not true. Consider the following view: (i) the functioning pacemaker inside some person’s body is involved in that body’s contribution to the instantiation of some of its properties, e.g., its circulatory properties, but (ii) the pacemaker is not a part of that body because it is not caught up in the body’s metabolic processes. I doubt that the conjunction of (i) and (ii) is true, because I doubt that (ii) is true. I am inclined to regard the functioning pacemaker as a part of one’s body (as explained in Section 4), and I deny that being caught up in the metabolism of the body is necessary for being a part of the body. However, I have no doubt that the conjunction of (i) and (ii) is a logically/conceptually coherent position. Of course, (i) entails that condition 2 of my analysis obtains in the case of the pacemaker, and (ii) entails that the pacemaker is not a part of the body. Since the conjunction of (i) and (ii) is a coherent position, it follows that the idea that condition 2 obtains does not presuppose that x is a part of body y. And since the proponent of (i) and (ii) would admit that condition 1 is satisfied in the case of the pacemaker, the idea that 1 and 2 both obtain does not presuppose that x is a part of body y.

My analysis of bodily parthood is not being offered as a definitional truth; it is not intended to be an account of the very meaning of ‘part’ or ‘body part’. The word ‘necessarily’ in my analysis does, of course, indicate necessity, but I do not insist that it is conceptual/analytic necessity. That is, conditions 1–3 are offered as necessary and jointly sufficient conditions, but they are not being proposed as conceptually/analytically so. They are proposed as metaphysically necessary and sufficient. Note, however, that even if 1–3 were conceptually necessary and sufficient for x’s being a part of body y, the analysis would still be highly informative. For example, one might initially be tempted to believe that the splinter is a part of one’s body simply because it is within the spatial boundary of the body. But by reflecting on whether the splinter is involved in the body’s contribution to the instantiation of its properties, one might decide that it is not a part of the body. One might start to think that the splinter itself is not involved in the contribution the body makes to the body’s mass, or its density, or its circulatory processes, etc., and as a result, one might conclude that the splinter is not a body part. Or we might have no idea whether the fetus should count as a part of the pregnant person’s body until we reflect on whether the fetus is involved in the contribution the containing body makes to the instantiation of the body’s properties. The fetus causally contributes in various ways to the properties of the pregnant person’s body. But is the former involved in the very contribution that the latter makes to the instantiation of those properties? Here arguments can be given on either side. The debate would not be easy, and the results would be informative, even if conditions 1–3 were conceptually necessary and sufficient for x’s being a part of body y. So even if I were offering my analysis as a conceptual truth, which I am not, there would be no unacceptable circularity (no more circularity than what is found in any accurate conceptual analysis (or valid argument)).

6. Recap

Based on the insights of others who have thought about parthood, I offered an analysis of bodily parthood in Section 4. Drawing on the core idea that what makes something a part is how it contributes to the whole, I presented an account that identifies what contribution to a body at a certain time is necessary and sufficient for being a part of that body at that time. My analysis does not emphasize the contribution to characteristic features of the whole. According to my account, the right sort of contribution to the features of a body, whether or not those features are characteristic, is sufficient for making something that lies within its spatial boundary a part of that body. More specifically, the contribution to the properties of a body that makes something a part of that body, on my account, is to be understood in terms of involvement in the instantiation of the body’s properties, i.e., the presence of the item being among that in which the instantiation of (at least some of) the body’s properties consists. And since internal items that are non-parts can contribute synchronically to properties of the body, my analysis requires that the parts are those that are involved in the body’s contribution to the instantiation of (some of) its properties.

In addition to hopefully providing some insight into the nature of parthood generally, the account of bodily parthood offered here helps to show that talk of the body is perfectly intelligible, contrary to the claims of some philosophers (mentioned in Section 1 and endnote 1); the account of bodily parthood provided reveals exactly what a body is, i.e., the aggregate of those parts the account tells us it has. The analysis of bodily parthood developed here might also be of some help when addressing philosophical questions regarding how we relate to our bodies (e.g., whether we are identical with them, are constituted by them, have them as proper parts, or are proper parts of them). Also, on the assumption that at least many of the parts of our bodies count as parts of us, the account can help us decide which items within the spatial boundaries of our bodies (e.g., a pacemaker, a brain implant, or a fetus) count as parts of us.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

The author declares no conflict of interest.

Notes

1	Olson (e.g., [2] (pp. 144–148)), ref. [5] (p. 247–248)) mentions and rejects what he calls the Cartesian Account of what it is to be one’s body, according to which, one’s body is that material object one can directly move and of which one is directly aware. Van Inwagen [1] objects to attempts to define one’s body as the bearer of one’s physical properties or as the bearer of physical properties commonly predicated of one. See Michael Tye’s [6] definition of ‘x’s body’, which aims to avoid van Inwagen’s objections. And see Olson’s [2] (pp. 148–149) objections to Tye’s account. See also David Hershenov’s [7] (p. 46) objections to Sydney Shoemaker’s characterization of a person’s body as “constituted by certain relations of causal dependence between states of that body and sensory and volitional states of the person” [8] (p. 287). See, also, Lynne Rudder Baker’s ([9] (p. 112), ref. [10] (p. 651)) proposals on what makes something one’s body.
2	Olson gives the label ‘biological minimalism’ to the view that “things (or at least material things) compose something if and only if their activities constitute a life” [13] (p. 226).
3	Olson makes the stronger claim that “no animal—no biological organism—could be partly or wholly inorganic” [5] (p. 253).
4	Vanessa Triviño and Javier Suárez [14] mention, in connection with Marie Kaiser’s [15,16] account of biological parthood, that “there are many units in the organism that contain proper parts that do not contribute to its function, as it happens with cysts in some organs” and “there does not seem to be any problem in accepting that macroorganisms can possess proper parts, such as organs, with deleterious functions, or with no function at all” [14] (p. 4).
5	I reject what Olson calls “corpse eliminativism,” the view that “strictly speaking there are no corpses, but only particles arranged corporeally” after your death [17] (p. 94); also see [18] (p. 268). And since I believe that a successful account can be given of the parts of non-living bodies, I do not agree with Hershenov that “a nonbiological analysis of the terms ‘body part’ and ‘foreign body’, that is, an analysis that does not identify body parts with being part of the living organism, is a massive confusion of conflicting intuitions which can only be ‘saved’, if it can, by some ad hoc conceptual gerrymandering resulting in a disjunctive account” [7] (p. 47).
6	Gillett [21] (ch. 2) also uses the labels ‘working entities’ and ‘working components’.
7	Peter Simons writes, “A part of a concrete individual […] is something which plays a distinct, unified and identifiable causal or, more broadly, functional role within the individual or its life” [23] (p. 609). Simons recognizes that the contribution might be to features of the individual other than life.
8	In what follows I will liberally quote from Kaiser’s 2018 paper [16], although some of the points quoted are also made in her 2015 book [15].
9	Kaiser [16] (p. 79) mentions and critiques Carl Craver’s [24] (pp. 139–160) account of “constitutive relevance.” Craver proposes that “X’s ϕ-ing is constitutively relevant to S’s ψ-ing if the two are related as part to whole and the relata are mutually manipulable” [24] (p. 154).
10	Kaiser [15] (p. 181) addresses the fact that Mackie presents the idea of INUS-conditions in an account of causation but parthood is typically considered non-causal. As Carl Gillett points out, “Compositional relations are non-causal determination relations that are synchronous” [20] (p. 317), “non-productive determination relations that are synchronous” [21] (p. 80). To capture the idea of synchronic determination, Gillett speaks of the properties of the parts realizing properties of the whole, and processes grounded by the properties of the parts implementing processes grounded by the properties of the whole [20,21,22] (ch. 2 of [21]).
11	Stuart Glennan’s [26] analysis of “corporeal composition,” discussed in some of what follows, includes time indices. (See Kaiser and Beate Krickel’s [27] discussion of constitutive mechanistic phenomena.)
12	As Triviño and Suárez mention, “Parthood relations in composite objects only concern the “glue” that is established among the parts of the composite object, irrespective of what happens in other objects” [14] (p. 5).
13	See also the passages from Triviño and Suárez [14] (p. 4) quoted above in endnote 4.
14	Glennan’s analysis is “(CC) X is a corporeal component of S during period t if, and only if (1) X and S are objects (2) S has a set of characteristic behaviors and capacities (hereafter CBCs) (3) X is a member of a set of at least two objects (X₁,…Xn) where each member of the set, by its CBCs, a. jointly and directly contribute to some of the composite’s CBCs during t, and b. exhibit cohesion with each other during the life of the composite” [26] (p. 11446). My analysis, presented in Section 4, avoids reference to characteristic behaviors or capacities. Another major way in which my proposal differs from Glennan’s is mentioned in Section 5.
15	The notion of being involved in utilized in my account might seem similar to the notion of helping make up that Catherine Sutton [29] uses to define composition, which she then uses to characterize constitution. But it is different. For Sutton, ‘x helps make up y’ = df. “Anything that overlaps x also overlaps y; and in the absence of y, x is matter or a thing that can be used to help form an instance of the y-kind into existence” [29] (p. 88). This is not the sense of being involved in that I am using to analyze bodily parthood, for my account allows that the following could obtain even if x is not actually a part of body y: x is spatially contained in body y, and in the absence of y, x could be used to form an instance of a body.
16	It is not clear that the minimally sufficient qualification solves the stomach + cotton ball problem even within the confines of Kaiser’s account. The stomach + cotton ball combo is engaged in a biological process, digestive activity, that is a necessary contribution to a condition, digestion occurring within body y, that is minimally sufficient for digestion occurring within body y, which is characteristic behavior of body y.
17	The motivation for this view is the belief that while the person and the body wholly spatially coincide, they differ in persistence conditions—for instance, with the person coming into existence at some point after the body does and typically ceasing to exist before the body does, much as the piece of marble exists before being sculpted into a statue and can outlast the statue by losing its statuesque form. Among the many supporters of the person-body constitution theory are two prominent defenders mentioned earlier in this paper: Baker, e.g., [9,30] and Shoemaker, e.g., [8,31].
18	Olson [13] (pp. 168–171) labels the view ‘compound dualism’ and emphasizes the word ‘soul’ in describing the view. Andrew Bailey gives the label ‘union dualism’ to the view that “we are amalgams: part material animal and part immaterial soul” [32] (p. 869); see also Bailey and Peter van Elswyk [33] (p. 406). To be clear, Olson, Bailey, and van Elswyk do not endorse either this or the next substance dualist view.
19	Olson labels it ‘pure dualism’ and describes it as “the view that we are souls and that we have bodies that are not parts of us” [13] (p. 168). Bailey gives the label ‘pure dualism’ to the view that “we are wholly immaterial souls, distinct from any animal” [32] (p. 869); and see Bailey and van Elswyk [33] (p. 406).
20	Bailey and van Elswyk [33] (p. 406) give the label ‘brainism’ to the view that “We are brains that are proper parts of animals.” See also Bailey [32] (p. 869). Supporters of a view along these lines include, among others, Jeff McMahan [34] (pp. 92–94), Tim Campbell and McMahan [35] (pp. 289–290), Derek Parfit [36], Roland Puccetti [37], Thomas Nagel [38] (pp. 40–41), and Michael Tye [39] (p. 143).
21	See Kaiser’s objections to interactionist accounts of parthood (e.g., [15] (pp. 179–180), [16] (pp. 77–81)).
22	In discussing potential problems for their bound state (“living objects”) view of organisms, Margarida Hermida and James Ladyman [40] (p. 23) mention living organisms with non-living and metabolically inert parts, including the outer layer of skin of most animals, which is composed of dead skin, and the outer parts of tree bark. While metabolically inert, Hermida and Ladyman point out that they do play a role in self-maintenance. However, it is not clear that these inert parts qualify as significantly interactive with other parts of the organism.
23	While Waechter and Ladyman [41] and McKenzie and Muller [42] offer bonding (of the right sort) as a necessary and sufficient condition for composition, Husmann and Näger [43] offer a disjunctive analysis on which composition arises if and only if there is bonding or the parts constitute a life.
24	McKenzie and Muller mention that Teller offered this counter-example during their presentation of the paper at the EPSA 2015 conference.
25	I do not address here whether being in a common bound state is sufficient for composing an object or for being a part of that composite. Van Inwagen [12] (pp. 56–71) rejects various criteria of composition involving some sort of physical bonding, including cases of fastening, cohesion, and fusion, claiming that “it is pretty clear that one cannot bring a composite object into existence by bonding two human beings—or two living organisms of any sort—to each other” (p. 62). I leave open here whether bound state theorists do or can adequately answer van Inwagen on this point. (For discussion see, e.g., Husmann and Näger [43] (pp. 68–71) and van Inwagen [45] (pp. 211–217).) But even if being in a common bound state is sufficient for forming a composite, it does not seem sufficient for being a part of the composite. In discussing potential problems for their bound state (“living objects”) view of organisms, Hermida and Ladyman mention, as an example of an inert object in a bound state with the living parts of an organism, that “chickens are known to swallow stones which play a functional role in breaking down food in the gizzard”; and as an example of a non-functional object that can be in a bound state with parts of the organism, they mention “a splinter lodged under the skin” [40] (p. 23). It seems to me that these are not parts of the body of the organism, despite being in a bound state with other parts of the body.

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