The Atlas of Reality
Page 78
We can now replace (14) and (15) with our final pair of necessities:
(16) If PnT, then: (i) if p, then PnFnp, and (ii) if PnGnp, then p.
(17) If FnT, then: (i) if p, then GnPnp, and (ii) if FnPnp, then p.
We will assume that we can limit our attention to that case in which ‘p’ corresponds to some simple, atomic (positive) proposition. If we can explain the universal and necessary truth of (16) and (17) in that case, it seems likely that the other cases (negations, disjunctions, quantificational propositions) can also be handled.
The necessity of (16) could be grounded in the temporal structure of the process or processes that link the present time with the past of n units ago. We have to assume that Tensers embrace an Aristotelian Modality (14.2A.5), and we have to assume that it is somehow necessary that only possible events occur. That is, if the truthmaker of p is part of a process P, it must be the case that P had p's truth among its possibilities from the very beginning. That is, if P was initiated m units of time ago, P must have included a truthmaker of Fmp at that time. All that we need is for the process also to have contained FmPnFnp at that time. Since we have Fmp, we will also have F(m-n)Fnp trivially. If we can appeal to the universal necessity of (17), we can replace ‘Fnp’ with ‘GnPnFnp’, resulting in F(m-n)GnPnFnp. We can now collapse the ‘F(m-n)Gn’ back to ‘Fm’, resulting in FmPnFnp. Thus, the fact that p and PnFnp would be simultaneously the case was already in the cards of process P from the very beginning.
If this is on the right track, then the necessity of (16) can be explained by combining Aristotelian Modality with the necessity of (17), on the assumption that possibility satisfies Actuality Entails Possibility:
Actuality Entails Possibility. Necessarily, if it is (now) the case that p, then it has always been possible that p be true now.
In addition, the necessity of (16) could be explained by reference to the necessity of causation. If every event in time must be preceded by a cause, Tensers could hypothesize that the cause of an event consists in some prior process with the power of producing that event. If the present event corresponds to p, such a prior process would have to have included a truthmaker for Fp, thus explaining PFp as a necessary consequence of p.
Let's turn then to the necessity of (17). Here we think Tensers must appeal to some fundamental, brute necessity. The passage of time just consists in the fact that actual, present nexuses successively ossify into higher-order nexuses involving some pastness trope. This is certainly a costly assumption about necessity (PMeth 1.2). Whether or not it is a decisive objection depends on whether Anti-Tensers can offer a simpler account of the flow of time.
21.7 Conclusion
Tensers have reasonably good responses to several of the standard objections lodged against them by Anti-Tensers, including the problem about the rate of the flow of time and McTaggart's paradox. Truthmaker objections are a serious challenge to Presentism and to Growing Block Tensism, but they pose no challenge to other versions of Tensism. In addition, Presentists have a variety of plausible ways of meeting this challenge, including past-tensed properties and tensed copulas.
There are a limited number of brute necessities that are inseparably part of the Tensers' account of the flow of time. Whether Anti-Tensism offers a simpler account is a matter that we will take up in Chapters 27 and 28, where we consider the problem of causal direction.
Special relativity offers the most straightforward objection to Tensism, at least as special relativity is usually interpreted by physicists and philosophers of physics. Tensers must suppose that there are metaphysical facts about absolute simultaneity that are empirically undetectable. This is a real cost. How significant it is depends on one's view of the weight of scientific practice as a criterion for metaphysical theory.
Part VII
Unity
22
Material Composition: The Special Question
In Part VII, composed of Chapters 22–25, we examine the problem of unity. In particular, we consider how it is possible for one thing to exist in and through a plurality of parts or phases. The unity problem has two dimensions, one spatial and the other temporal. In the spatial case, one worries about how a plurality of things can compose a single whole at the same time. In the temporal case, the problem concerns how a series of intrinsically variegated phases can be stages in the existence of a single, persisting thing. The spatial dimension occupies us in this chapter and the next, and the temporal dimension occupies us in Chapters 24 and 25. In fact, Chapter 25 combines both dimensions of the problem of unity, since we consider there the persistence through time of spatially composite things.
This chapter begins with a general discussion of the existence of composite things (Section 22.1). Then we consider (in Section 22.2) the view that composite entities are always an “ontological free lunch”, things that can be freely posited without incurring any cost in relation to ontological economy or Ockham's Razor. Next, we look at the issue of causal redundancy (Section 22.3), a consideration which suggests that positing composite entities as fundamental things is in fact quite costly, something to be undertaken only with strong reasons.
In the next three sections we examine three candidates for fundamental composite entities: heaps (Section 22.4), artifacts (Section 22.5), and organisms (Section 22.6). We finally turn to the question of which sorts of composite things exist at all, whether fundamentally or derivatively. This involves a search for an intelligible principle of composition (Section 22.7).
In the following chapter, Chapter 23, we will investigate the nature of the part-whole relation itself.
22.1 The Existence of Composite Things
Much of this chapter will be concerned with three questions. First, do any composite things (things having parts) exist at all, and, second, if so, which ones? These two questions should be distinguished from a third question: are any composite things metaphysically fundamental (as in, G-fundamental Def D3.5)? A fundamental entity is one whose existence and intrinsic character are not grounded in other things. We look at this third question Sections 2.3 through Section 2.6, returning to the first two in Section 2.7.
In Material Beings (van Inwagen 1990a), Peter van Inwagen introduced the distinction between the general and special composition questions:
General Composition Question: what is it for one thing to be a part of another?
Special Composition Question: when do some things compose a further thing?
We take up the General Composition Question in Chapter 23. This chapter focuses on the Special Composition Question. There are two versions of the Special Composition Question, one Narrow and one Broad. The Broad version asks, when do some things compose anything at all? The Narrow version asks, when do some things compose a fundamental thing?1
We consider three positive answers to the Narrow version: (1) things compose something fundamental when they are spatially connected or continuous, (2) things compose something fundamental when they are parts of an artifact, and (3) things compose something fundamental when they compose a living organism. And we consider a negative answer, Priority Atomism, according to which nothing ever composes anything fundamental. Before arriving at these answers, however, we consider two issues about composite things, namely, whether they are an “ontological free lunch” (Section 22.2), and whether they are redundant vis-à-vis their parts (Section 22.3).
22.2 Are Composite Things an “Ontological Free Lunch”?
David Armstrong (1997) argued that we should treat composite entities as an “ontological free lunch”. In other words, the number and variety of composite entities that are entailed by a theory shouldn't count against its simplicity. We shouldn't apply Ockham's Razor (PMeth 1), which directs us to prefer the more economical or parsimonious theory, on the basis of a theory's commitment to composite entities. Only atomic entities, entities without parts (or ‘proper parts’, as modern mereologists prefer to put it), should be counted.
There are two possible reasons for embraci
ng Armstrong's free lunch principle: (1) facts about wholes and facts about their parts are really the very same facts: differences between truths at different mereological levels are metaphysically equivalent, and only conceptually different, or (2) facts about wholes are always reducible to (wholly grounded in) facts about their parts. The first possibility requires something very like the theory of composition as identity, proposed by Donald Baxter (1988), according to which wholes just are their parts, taken collectively. Thus, if we have some things, then to say that something exists that contains them as parts is just another way of saying that those same things exist. We examine Composition as Identity (23.1T.1.1) in more detail in Chapter 23.
This first option also requires that there be no metaphysical priority of parts over wholes or of wholes over parts. Something cannot be prior to itself, so if wholes just are their parts, then neither level can be prior to the other. Here is a breakdown of the relevant theses:
22.1T Universal Compositional Priority. Whenever some parts compose a whole, either the parts are wholly grounded in the whole, or the whole is wholly grounded in the parts.
22.1T.1T Universal Bottom-Up Priority. Whenever some parts compose a whole, the whole is wholly grounded in the parts.
22.1A No Universal Compositional Priority. There are cases of composition in which neither the whole is wholly grounded in the parts, nor are the parts wholly grounded in the whole.
22.1A.1T No Compositional Priority. In cases of composition, the whole is never wholly grounded in its parts, nor are the parts wholly grounded in the whole.
22.1A.1T.1 Compositional Equivalence. In cases of composition, truths about the whole and truths about the parts are metaphysically equivalent.
Given these theses, we can identify the two ways of defending the free lunch principle: Compositional Equivalence (22.1A.1T.1) and Universal Bottom-Up Priority (22.1T.1T). Compositional Equivalence forces us to clarify what could be meant by ‘metaphysical equivalence’. We could take it as a new primitive, conveying the idea that two true propositions say the same thing about the world. If we adopt some form of Truthmaker Theory (2.1T/2.1A.1T), metaphysical equivalence can be having the same truthmakers in every possible situation. Finally, if we adopt some form of Real Grounding (3.1T), we could suppose that two propositions are metaphysically equivalent just in case they are both wholly grounded in the truth of some third proposition. We presently take up this last possibility.
If all truths concerning composite entities and their parts are wholly grounded in other truths, then the fundamental truths must describe a composition-free world. What could such a world be like? It would seem that there are just two possibilities. It could be a Nihilist (11.1A) world, or it could be a world in which all the fundamental truths are truths about simple entities. If the fundamental truths of the world include truths about things at all (whether one or many), and these fundamental truths are composition-free, then those fundamental things will count as mereological atoms (as simple entities), in which case those atoms will necessarily be metaphysically prior to all composite entities. In order for the fundamental truths to be composition-free, it must be the case that the fundamental atoms never combine into fundamental wholes. In fact, it seems that they could not (consistent with Compositional Equivalence) combine into wholes at all. If they did, wholes would be wholly grounded in their parts. So, on this view, either there are no fundamental entities at all, or the fundamental entities are all uncombinable atoms. In either case, the fundamental level of reality wholly grounds all the facts about composition and parthood. Thus, there are two versions of Compositional Equivalence:
22.1A.1T.1.1 Nihilistically Grounded Composition. All truths about wholes and their parts are wholly grounded in a class of nihilistic truths (truths that do not entail the existence of anything).
22.1A.1T.1.2 Atomistically Grounded Composition. All truths about wholes and their parts are wholly grounded in a class of truths about atomic things that never compose anything.
Nihilistically Grounded Composition can be readily combined with a certain metaphor or picture: that of reality as a mass of undifferentiated dough that we divide (by means of our conceptual cookie-cutters) into discrete things, some of which can be parts of others. On this view, the fundamental level of reality consists in this thing-free dough, and all things are derivative in status.
For now, let's turn to the second idea, that wholes are free lunches because their existence and their properties are reducible to those of their parts. The idea is that composite entities are nothing “over and above” their parts, as Armstrong puts it.
What do we mean by ‘reducibility’? As we saw in Section 3.1.5, it is not enough that the existence and the properties of the whole supervene (Def D2.6) on those of the parts. Supervenience merely tells us that we can't have any change in the property of the whole without some corresponding change in the properties of the parts. However, supervenience is not asymmetric, and reduction must be (see Section 3.1.5).
Cases of reduction are cases in which the reduced facts are wholly grounded in the reducing facts, as we argued in Section 3.1.5. Reduced facts exist by virtue of the existence of their reducing facts. If wholes were reducible to their parts, then it would follow that only atomic or partless things are fundamental. This would make wholes, if not a free lunch, at least an ontological cheap lunch, since Ockham's Razor (PMeth 1) applies most forcefully at the level of fundamental things. When a theory entails the existence of additional reducible things without entailing the existence of additional fundamental things, we do not usually count this against the theory (or, at least, not very much; see Section 3.9).
What about those, like Quine, who reject metaphysical fundamentality? Let's assume that they also reject Composition as Identity. Such philosophers must deny Armstrong's free lunch principle.
There are, however, two necessary qualifications to this otherwise happy result. First, we might find some grounds for believing that composite things of kind K do or do not exist simpliciter, grounds that do not depend on their supposed fundamentality. So, we will have to distinguish hard and soft anti-realists. Hard anti-realists about some kind of thing deny that such things exist at all, while moderate or reductive anti-realists about some kind merely deny that such things are fundamental. We must track this difference.
Second, some philosophers reject both fundamentality and Ockham's Razor. It is hard to find anyone who is completely indifferent to Ockham's Razor. Most agree that it is problematic if a theory posits the existence of fairies, round squares, phlogiston, ordinary matter that travels faster than light, and so on. However, one might adopt a more limited version of Ockham's Razor, one that exempts kinds of things whose existence is a matter of common sense. We might value theories that agree with common sense or with ordinary experience, without insisting that such things are fundamental in some metaphysically serious way.
22.3 Redundancy
We often think that composites are not fundamental. One reason for thinking so is that the whole does no further work, above and beyond the work done by its parts. To use the language of Chapters 4 through 6, all of the powers of the whole consist in the possession of fundamental powers by its parts. Imagine, for example, a block of stone sliding along the surface of an icy lake. The stone possesses a certain kind of causal power to move things, based in its total momentum and kinetic energy. The momentum and energy of the whole stone, however, is nothing but the sum of the momenta and energies of its constituent atoms. The stone as such adds nothing new. We could describe the result of the block's striking another block on the lake by referring only to the fundamental particles making up the two blocks. Their inertia and mutual interactions could fully explain the results we observe. There is no scientific reason to introduce either block as a further agent, in addition to their constituent parts.
This observation suggests a methodological principle: a theory should posit fundamental entities of a certain kind only if they are needed in giving a
complete inventory of the world's causal powers. This principle is defended by Trenton Merricks (2003). Here's a first draft of such a principle:
Redundancy. Reject any theory that posits fundamental entities whose causal powers are redundant, given the other fundamental entities posited by that theory.
As we saw in Chapter 6, causal powers come in four varieties: active, passive, and immanent powers, and tendencies. Are all four kinds of power relevant to Redundancy? The one kind that seems questionable in this respect is that of passive powers. Suppose that a kind of entity K is wholly redundant with respect to its active and immanent powers and its tendencies, but which had passive powers that could not be accounted for in terms of the passive powers of its parts. One possible example of this would be the human soul as conceived of by the theory of epiphenomenalism. According to epiphenomenalism, the soul has no active or immanent power, and so no tendency. Everything that happens happens because of the action of one or more material bodies. However, the soul is affected by the state of the body in ways that cannot be accounted for in physical terms. The soul has experiences and feelings that are irreducible, on this account.
One of the difficulties with epiphenomenalism is that it is hard to see how we could know that we were having experiences in our soul if these soulish experiences had no active causal power over anything, including other states of the soul. How can we explain introspective belief and knowledge if the experiences we're introspecting are causally inert? This point might be resisted by positing a form of knowledge, namely, direct acquaintance, that doesn't require any causal efficacy on the part of the object. Logical and mathematical knowledge is often supposed to be of this kind, on the assumption that logical and mathematical entities are causally inert. (For a different view, see Koons 2000.)