Dispositions, Supervenience and Reduction Stephen Mumford The Philosophical Quarterly, Vol. 44, No. 177. (Oct., 1994), pp. 419-438. Stable URL: http://links.jstor.org/sici?sici=0031-8094%28199410%2944%3A177%3C419%3ADSAR%3E2.0.CO%3B2-2 The Philosophical Quarterly is currently published by The Philosophical Quarterly.
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7.h Philosophical Qyurterb Vol. 44, No. 177 ZSSN 0031-8094
October 1994
The Philosophical Quarterly DISPOSITIONS, SUPERVENIENCE AND
REDUCTION
I. INTRODUCTION
There'is good reason to believe that dispositional and categorical properties can be identical in their instantiations. This thesis can be called 'property monism'.' There is more than one way to interpret this 'property monism', though. It may mean: 1. Dispositions just are nothing over and above categorical properties, or
2. Categorical properties just are nothing over and above dispositions. It is one question whether or not we equate dispositions and their putative 'categorical bases'; it is another question which kind of property is fundamental and which reducible. In this paper I shall concentrate on the second question, and assume an identity thesis. I shall, however, consider some of the objections to identity in §V. Consider this question: if it is correct to identify the two types of property, should we go on to agree with Quine (The Roots of Reference p. 1 l), as follows? Each disposition, in my view, is a physical state or mechanism. A name for a specific disposition, e.g., solubility in water, deserves its place in the vocabulary of scientific theory as a name of a particular state or mechanism. In some cases, as in the case nowadays of solubility in water, we understand the physical details and are able to set
' See my article on dispositions and bases forthcoming in Ratio 8 (1995). Q The Editors of 7hc F'hilo5ophicd @mte75,1994. Published by Blackwell Publishers, 108 Cowley Road, Oxford OX4 IJF, UK and 238 Main S v e e ~Cambridge, MA 02142, USA.
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them forth explicitly in terms of the arrangement and interaction of small bodies. Such a formulation, once achieved, can thenceforward even take the place of the old disposition term, or stand as its new definition.
Though Quine discusses disposition 'terms' here, we can see that there is a firm ontological commitment: all that exists is (categorical) states, mechanisms, and bodies. Disposition terms are just vague, pre-scientific and inaccurate ways of talking about things which in reality are categorical properties. Of the two positions listed above, (1) corresponds to a Quinean categoricalproperty monism, (2) to a Popperian dispositionalproper&monism. Both, in including a 'nothing over and above' clause, make reductive claims, and in this paper I shall examine the justification for such reductions. I shall concern myself almost entirely with the reduction of dispositional to categorical properties, but if dispositional monism is offered as a serious ontological thesis then the argument I give will be applicable to it mutatis mutandis. I argue in this paper that reductionism of dispositions, in certain circumstances, is an empty claim, and Quine's reductionism is a case of this kind. I argue that reduction, in these cases, is respectable only as a logical or epistemological claim, not as a device for cutting away excess ontological baggage. That an ontological reduction in the case of dispositions proves to be empty ought to be regarded as a cause for concern about analogous reductionist claims in other domains. I shall be able to say very little about the general problem here, though I shall show where the problem lies. 11. REDUCTION
The form of reduction I discuss in this paper can be called 'ontological reduction', and can be understood, initially, as an application of the principle of Occam's razor, i.e., a method of eliminating unnecessary entities from our list of the world's contents. Let us examine the claim that one class is ontologically reducible to another. I shall call one (X)the reduced class and the other V ) the reducing class. What does a reductionist claim about K and J amount to? We can extract something general from the following: Reducibility, as usually understood, involves either the definitional equivalence or the nomological equivalence of property-expressing predicates; often it is construed as involving the underlying identity of the properties expressed by such equivalent predicates (Horgan p. 29). O The Editors of 7he Phthsophicol Qunrtob, 1994.
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[in temperature] we have a paradigm of a physical property, one that has also been cited as the paradigm of a successfully reduced property as expressed in the intertheoretic identity 'temperature = mean kinetic energy of constituent molecules' (Churchland p. 41).
These accounts make similar demands of reduction; a reduced term or class of terms must designate the same individual(s) as the reducing term or class of terms, so that inter-theoretic translations are possible between the two terms or classes of terms. I call this the co-extension requirement of reduction: [C] 7 ? co-extension ~ requirement: If a class Xis reducible to a classJ, then members of K must have identical extensions to members of J.
The translation takes the form of an identity statement connecting terms of the different classes, as exemplified in the identity statement 'temperature = mean kinetic energy of constituent molecules'. We can call these identity statements 'bridge laws', as they form the bridges between the two classes of terms.2 In the previous example we have a bridge between a term in the class of phenomenal physical terms and a term in the class of more sophisticated physical theory. All these features come into play in Fodor's characterization of reduction:
... A necessary and sufficient condition for the reduction of formula (1) to a law of physics is that the formulae (2) and (3) should be laws, and a necessary and sufficient condition for the reduction
of S to physics is that all its laws be so reduced.3
'PI' and 'P,' are supposed to be predicates of physics, and formula (3) is supposed to be a physical law. Formulae l i e (2) are often called 'bridge' laws. Their characteristic feature is that they contain predicates of both the reduced and reducing science (Synthese 1974 p. 1 12).
We can sum up so far by saying that for any two terms k and j from the classes K and J, an ontological reduction requires that the state of 2 Thus our reduction corresponds to Peacocke's nomological, rather than semantic, reduction (Holistic Explanation p. 172). 3 is a transitive and asymmetrical relation which could be taken to mean 'causes'. '04' is a symmetrical relation to indicate co-extension. '-03
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affairs designated by k and j be the same. But is this a sufficient condition for reduction, as Fodor seems to suggest? We quickly see that it is not, and that the views canvassed thus far are wholly inadequate for an ontological reduction. An ontological reduction makes a claim about what there real& is and what there real& is A symmetrical relation, such as that of co-extension, is completely incapable of such a determination. Let us assume that j* and k* satisfy the co-extension requirement; which ofj* and k* is the reduced term and which is the reducing term? Put another way, which state of affairs, property or event is claimed to be real and which reducible, that designated by j* or that designated by k*3 O n the sole basis of co-extension there is no determination; j* may be reducible to k* or k* to j*. Clearly, if co-extension were the only requirement for reduction, reduction would be an empty relation to posit. If reduction is to mean anything at all it must be an asymmetrical relation. What are we to make of reductive claims which offer no more justification than an identity between two classes of terms specified in bridge laws? If this is the only justification, then the reductive claim is based on ontological prejudice, for example, on a faith in the primacy of one 'science' over another. If one were to say that all terms referring to mental events were translatable, through bridge laws, into terms referring to physical events, then a claim that the mental was reducible to the physical would reveal only an ontological bias towards physicalism. The 'bridge' of the inter-theoretic identity can be crossed both ways, so physical event terms can be translated into mental event terms and there would be equal justification for the reduction of the physical to the mental. All this has parallel relevance in the case of dispositions. We may grant Quine his claim that water-solubility, and every other disposition, is some 'physical state or mechanism', but if this is to be interpreted as an identity statement then it is also correct to say that some physical state or mechanism is water-solubility. The reducible term is underdetermined and Quine reveals his ontological bias towards categorical properties in claiming otherwise. What do we need to add to the co-extension requirement if we are to have a necessary and sufficient condition of reducibility? What must For instance: 'The general conceptual system not only provides the mechanism for explaining, for instance, the observed relations between calorific phenomena, but at the same time provides materials for acceptable claims as to what calorific phenomena "really" are' (Harre, Matter and Method p. 38). O The Editan of 7he Ailo~ophical(LumInb, 1994.
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be added is some notion of the supervenience of the reduced class on the reducing class: [ S ] 7 h e supelvenience requirement: If a class Kis reducible to a class 3 , then all K-terms must supervene on 3-terms.
Supervenience is understood to be an asymmetrical relation, which would therefore purport to add the asymmetry lacking from the notion of reduction thus far. Bringing the two requirements together, we have the following proposed necessary (and possibly sufficient5)conditions for reduction: [ R ] : A class of terms X i s reducible to a class of terms 3 if and only if i. each K-term is co-extensive with a 3-term, ii. such K-terms supervene on 3-terms.
The notion of supervenience itself cannot be taken as unproblematic. I shall show that supervenience suffers from all the same problems as reduction did when based solely on the co-extension requirement, and thus that it cannot save the notion from the vacuity into which it collapses.
111. SUPERVENIENCE
Supervenience can be understood as a relation of dependence of a 'supervenient' class upon a 'subvenient' class. How is such a dependence to be understood? Davidson's original formulation (for the case of psychophysical supervenience) was: supervenience might be taken to mean that there cannot be two events alike in all physical respects but differing in some mental respect, or that an object cannot alter in some mental respect without altering in some physical respect ('Mental Events' p. 214).
It should first be noted that the two disjuncts in this definition are not identical. The first would allow that at a time t,, both events el and e, were alike in the physical respect P, and therefore alike in the mental respect M, but at a later time t,, el and e, are still alike in respect of P, but are alike in a different mental respect M,. The first definition Charles and Lennon describe other proposed conditions of reduction, and Nagel gives a much longer' list than I. But I think that the requirements [S] and [C] are the only necessary conditions of the attempted reductions with which I am concerned. Whether they can be deemed' sufficient is a pointless debate because, as I shall show, [S] and [C] form an inconsistent set. O The Editors of 7he Phrlosophicd Qunrfer!~, 1994
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merely states that alikeness in physical respects entails alikeness in mental respects, but the mental respects in which physically type-identical particulars are alike may vary over time, and this is inconsistent with Davidson's second definition. The second definition does not entail the first either, for it would be consistent with two physically alike particulars' being unalike in their mental respects. The first definition has been repeated in numerous discussions of putative superveniences: Consider first the claim that psycho-physical predicates are supervenient on physical predicates, in the sense that there cannot be two situations agreeing in all physical respects but differing in some psychological respect (Peacocke p. 48).
A property P supervenes on a set of properties B if and only if when two entities are indiscernible with respect to their possession of B-properties, they are indiscernible with respect to their possession of P (Charles p. 267; see also Teller p. 145 and Horgan p. 40).
What is really important about supervenience, however, is not that two things do agree in all subvenient properties, but wb t h q would be alike in supervenient properties if they did agree; hence we are warranted in referring to other possible worlds to find a 'subveniently alike' counterpart. The reason why supervenient properties would be alike in such cases can be expressed as that the subvenient properties determine or 'fix' supervenient properties. This line is followed in a number of places: one class of properties supervenes on another if the presence or absence of properties in the former class is completely determined by the presence or absence of properties in the latter (Stich p. 574). once the descriptive or naturalistic properties of a given object are wholly fixed, its moral and evaluative properties are also thereby fixed (Kim 1984 p. 45; see also Kim 1978 p. 155).
In the case of reduction, such 'king' cannot be causal, for here we have co-extensive terms, i.e., an identity relation, and nothing can be the cause of itself. What, then, is the k i n g relation? The best we can say is this: if we identify a subvenient property by a J-term specification, we thereby limit ,the specification of the supervenient K-term. Because a J-term specification is satisfied a K-term is also satisfied, so there could not be a state of affairs correctly describable as, say, j*, which was not correctly describable as k*, though there may be some empirical investigation as to what K-term is to be correlated with what J-term in a bridge law. Put yet another way, we can express the relation as that whenever j * is the case k* must also be the case, but not vice versa. O The Editors of 7he Philosophical Quark+
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Why must the supervenience relation be asymmetrical? Reduction based on nothing more than a co-extension requirement was shown to be vacuous in that it could not distinguish the reduced from the reducing. Clearly the same applies to the supervenience relation. This must be an asymmetrical relation if the supervenient and subvenient are to be distinguished so that the relation can mean anything. I therefore take it that the defenders of supervenience intend the relation to be such that, if k* supervenes on j*, then necessarily it is not the case that j * supervenes on k*. This condition I am prepared to take as a necessary condition of the very significance of the concept. H.A. Lewis has suggested (p. 163) that this relation simply does not obtain in many cases: The formulations mentioned above invite us to entertain the possibility of another object or event that shares all (relevant, subvenient) properties with the first: such another would then share the supervenient properties. But for many examples of determination, this will not hold. Winning a race is determined by other properties, but if two people share all those properties, neither is the outright winner. The value of a rare postage stamp supervenes on its physical properties but is also determined by its uniqueness: the existence of a physically indiscernible stamp would lower its value.
Though I wish to argue against the notion of supervenience, I think such counter-examples fail. First, winning a race depends upon being the first to cross the line: what if two runners cross the line at exactly the same time? If both have this subvenient property then both would have the supervenient property of being winners, or joint winners. All that supervenience declares is that $two individuals are alike in subvenient properties then they are alike in supervenient properties. Being the outright winner of a race must be seen as a relational property, in that it is in part determined by no other runner's crossing the line either before or at the same time. The example is thus a loaded one, for no two runners could bear this relation to the rest of the field. We could imagine two runners in different races, both of whom had the relational property of crossing the line before anyone else in their own race. In this case they would be alike in subvenient properties and hence alike in supervenient properties. Likewise if two competitors both had the property of crossing the line at exactly the same time as one other competitor but before all others, then they would also be alike in respect of the supervenient property of being joint winners. Similar'points can be made against the postage stamp example. If there was a postage stamp, the penny green, previously believed to have been unique but now known to be one of two in the public O The Editors of % Philorophlcd Qumfnb, 1994
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domain, then these two stamps, if they are physically indistinct, ought to be of equal value, even though this value would probably be less than that of the previous 'unique' penny green. Thus 'alike in subvenient properties - alike in supervenient properties' holds. As with winning races, the matter is not that simple, however. Market prices depend on a host of relational properties. Contrary to classical economic theory, we are not 'rational' purchasers, and a wealthy collector may be prepared to pay a price for one penny green which no dealer could hope to see repeated for the second. Other relational properties may affect the market price; one stamp may have been manufactured before the other or one may have previously been among the collection of Elvis Presley: all such factors would have to be taken into account. A similar putative counter-example6 concerns the value of a painting. Suppose I manufactured a physically indiscernible copy of irhe Last Supper. Should not this copy have a market value equal to that of the original? Of course not; the market value of a painting is partly determined by its origin, a relational property, but one which nevertheless would have to be included in our subvenient 'base' of value. This is a defence of supervenience against some alleged counterexamples, but it does not constitute a justification of the notion: it only narrows down the scope of the attack. In the next section I shall make that attack, which will be seen as no less devastating despite our having excluded the alleged counter-examples. IV. DISPOSITIONS AND THE DIRECTION OF SUPERVENIENCE
If dispositions are identical with the intrinsic causes, in the object, of their manifestations given a stimulus, i.e., causes which are called, as is conventional though not necessarily ontologically accurate, categorical bases, what follows about supervenience? Identity alone would not secure the supervenience of dispositions upon categorical bases, nor the converse. If, however, dispositions can be shown to supervene on categorical bases, then a reduction of the dispositional is possible. I argue now that an alleged supervenience between the dispositional and the categorical is a n . empty notion; thus the reduction of dispositions to their putative bases is equally empty. Supervenience may, on occasion, be a useful notion. We can sensibly say that the writing of Plato's dialogues supervened upon Socrates' execution, or 'that the flame supervened upon striking the match. These Again from H.A. Lewis, in conversation. 8 The Fditon of 7hc Philosophical Quor&h, 1994.
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cases could be challenged as to their truth-value, but not as to their informative content, for, unlike the cases I am concerned with, they say something significant. Equally, we could say that the value of a postage stamp supervenes upon its physical properties and its relation to certain facts about demand and supply. These alleged superveniences differ from the cases I wish to consider in that they are not allegations of superveniences between identicals. Plato's writing the dialogues was not the same event as Socrates' drinking the poison: hence the supervenience involved could have a causal aspect. Similarly, value is not the same property as the physical and relational properties of a postage stamp. For the ontological reduction that the reductionist wants, we must allege a supervenience between identicals, given that, on the above analysis, both identity and supervenience are necessary conditions of such a reduction. It is thus only supervenience within identity which is the target of my attack. It should therefore be noted that I am not attacking the explicit supervenience claim which Prior (1985 p. 89) makes for dispositions upon categorical bases; dispositions and bases are not identical in. her ontology. The target of my attack, rather, is the implicit superveniences suggested by the reductive identity theories of Quine (pp. 8-1 5), Armstrong (pp. 85-8) and Mackie (ch. 4). Let us consider the alleged supervenience of a disposition on a socalled categorical base. I begin with a simple example to illustrate my argument: the disposition (d*) of a billiard ball to roll in a straight line on a flat surface when struck. Allegedly, this disposition supervenes upon the 'actual' (categorical) properties of the billiard ball (I take it that there is just as good a case for saying that dispositions are actual properties). But clearly this is not precisely what is intended here,7 for d* does not supervene upon all the categorical properties of the billiard ball; many of its properties will be irrelevant to the possession of the disposition. These properties, we shall say, are impotent with respect to the determination of d*. Following Griffin, we can call this the 'relevance requirement'. Which properties can we discard as irrelevant? We could discard, for instance, the material composition of the billiard ball, for the same disposition can be possessed whether the ball is made of ivory or plastic. We can discard the colour of the billiard ball, for whether it is red or white or any other colour the same disposition is possessed. Such properties, which we discard from our list of candidate subvenient properties, may well 'support' other dispositions, different from d*. For instance, they may support its disposition of impenetrability or its disposition to reflect light in a certain way. Indeed, there is a strong case Cf.H.A. Lewis pp. 16CFl; and Griffin p. 314. O The Editon of 7 h e Philmphud QuorUrb, 1994.
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for the claim that any real property must 'support' at least some disposition. Our concern, however, must be only with the properties relevant to the determination of d*, though the same argument will apply to all other dispositions. Various things can roll, but what something must possess if it is to have the disposition is a surface, various points of which come into contact, at different times, with the surface upon which it rests, so that a change of location is possible. The disposition to roll an indefinite distance, under suitable circumstances, is possessed by both wheels and billiard balls; all that is necessary for this disposition is the possession of a single circumference which is rigid to a certain degree. Thus a further disposition of the material which composes the object is relevant here, for it must not crumble as soon as it begins to move. A billiard ball can do something a wheel cannot, however: it can roll instantly in any direction, according to where it is struck, whereas a wheel is limited to certain directions. There must be some difference in the actual properties of the ball and wheel which accounts for this difference of disposition and the obvious difference is that the ball has an infinite number of circumferences. Finally we must add to our list of candidate subvenient properties something to account for the ball rolling in a straeht line. It does so because it is composed of a substance of even mass throughout; its centre of gravity is at the geometrical centre of its circumferences. If it did not have this property, it would roll in an arc. I have arrived at a plausible candidate for the categorical property to which the disposition d* is identical, namely, the possession of an infinite number of hard circumferences and a centre of gravity equidistant from all points on them. We could call this the 'property-complex' of being an equally balanced rigid sphere, or 'complex c*'. The full details of c* can only be discovered by empirical investigation, which I leave to others. What justification have we for the claim that c* names a subvenient property and d* a supervenient property? Thus far, we have succeeded only in flling in some of the details of the identity statement for d* and c*, but the direction of supervenience is undecided. What is the determination with respect to the following three supervenience criteria?
1. If K-terms supervene upon J-terms, then there cannot be two particulqrs alike in all J-respects but differing in K- respect^.^ Davidson's first definition above, followed by Peacocke, Teller, Charles, Horgan and Kim's first definition (1984 p. 45). O The Editors of 7hc Hihophicol @In&,
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2. If K-terms supervene upon 3-terms, then an object cannot alter in some K-respect without altering in some J-re~pect.~ 3. If K-terms supervene upon 3-terms, then the specification of all J-terms fixes, i.e., completely determines, all K-terms.lo Can we determine, employing these criteria, the subvenient and supervenient among d* and cX? Does rolling when struck supervene on being an equally balanced, rigid sphere, or vice versa? Criterion I: According to the analysis of d* I have given, there is indeed no way two particulars could be alike in possessing c* and yet differ in respect of possession of d*. But this does not suffice for the conclusion that c* is a reducing U) term and d* a reducible (X)term, for the converse equally holds. No two particulars could be alike in possession of d* and differ in respect of possession of c*. Any particular which possesses the disposition to roll when struck must have the categorical properties I have suggested, any other categorical properties it possesses being incidental. It may be wondered what modality is involved here. The categorical property c* to which d* is correlated is indeed correlated contingently, but only in so far as the laws of physics are contingent. Given certain laws of nature, the correlation of c* to d* is necessitated (more on this in the next section). According to criterion 1, therefore, d* has as good a claim to be the reducing property and c* the reducible property as contrariwise. Therefore criterion 1 fails as a criterion of supervenience. Criterion 2: Does the second criterion prove any more successful? Certainly if some object alters in respect of gain or loss of d*, it must alter in respect of gain or loss of c*, but again the converse holds. A gain or loss in respect of C*would be a gain or loss in respect of d*, and the required asymmetry of supervenience is lost. In effect, if the disposition to roll when struck was lost then the categorical property which we identified with the disposition must also have been lost, a fact which, contrary to the categorical monists, would make categorical properties supervenient on a disposition. Criterion 3: Here we have perhaps the most natural sense of supervenience - that of determining or 'fixing': we quickly see that it fares little better. Fix the categorical properties of a particular and we thereby fix its Davidson:~second definition, followed by Papineau @. 66): 'such categories as the psychological, the biological, the meteorological, the chemical, and so on, suparae on the physical, .in the sense that two situations cannot differ psychologically, or biologically, or whatever, without differing physically'. l o Stich; and Kim 1984. 6 The Editon of % Philosophlcd (Lunrtnh, 1994.
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dispositional properties; but the converse now holds also. In my billiard ball example I did begin by fixing or specifying a dispositional property, and I was then able to arrive at the categorical properties necessary for this disposition. By fixing the dispositional property I fixed the categorical property, which, under criterion 3, would have made dispositions subvenient, but as the same criterion could render the categorical properties subvenient simultaneously, we had better say that the criterion is inadequate. AU three criteria have failed for the same reason: failure to distinguish the subvenient and the supervenient. It is worth noting that the argument applies whatever the modality involved, i.e., it applies for weak and strong and all other brands of supervenience. The modality is not the issue. We cannot accept a notion of supervenience which allows two particulars to supervene upon each other, for such a notion is completely empty (and the same problem destroys the 'asymmetry guarantors' listed by Charles and Lennon, editorial introduction p. 16). It seems that we must give up our claims to supervenience, and reduction as well. Before I complete the argument, however, I need to consider some possible objections to the account.
V. OBJECTIONS I shall deal with two possible objections to the account: that the example I have given cannot be generalized to other dispositions; and that the putative identities do not hold. 1. Generalizing the Account. I illustrated my account of the problem of supervenience with a relatively simple example, but it may be wondered how the account could possibly be generalized to all dispositions. What is significant about the identity I drew between d* and c* is that the disposition and its putative base were QpcQpe identical. A strong case can be made for the claim that if identity relations between dispositions and bases are to hold at all they must be tokentoken identities. Dispositions appear to be 'multiply realized' in the way that Mackie suggests (p. 148): a cloth's disposition to absorb water has two different bases, absorbing water into the fibres and also into the spaces .in between the fibres. Further examples are salt and sugar, which possess the same disposition of solubility despite differing in their O The Editon of '& Htlosophicol (Lunr&&, 1994.
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categorical properties; fragility, too, is present in all sorts of objects which differ structurally. How could every instance of breakability be identical to one particular type of categorical property-complex, when so many different things can break? These considerations seem to tempt us towards a multiple realizability thesis: that various different categorical properties could realize or produce or instantiate the same dispositional property. If we are to remain property monists and accommodate this claim, then we have little option but to admit only token-token identities, that is, to claim that although we cannot say that all instances of a disposition D are identical to a type of categorical property C, we can preserve the identity relation if we allow that each instance or token di is identical to an instance or token of a categorical property c, ... c,. How are we to accommodate the apparent counter-examples in our defence of type-type identity? We do so by adopting the strategy, in all cases, of disregarding properties impotent with respect to determining the disposition. Once this is done, we find in each case that just, a single categorical correlate, no matter how general, can be found for each disposition. As P. Smith notes (p. 39), just because type-type identities are inconceivable at one level, this does not mean that there cannot be type-type identities at a higher level of abstraction. This can be illustrated with a completely theoretical example. Suppose we have a disposition, which various substances possess, which we can call 'A-combinability', namely an ability to combine with substance A to form compounds. Suppose now we have two structurally differing substances, B and C, both of which are A-combinable. What are the properties of B and C that are relevant to being A-combinable? This will be an a posten'on' matter, in that empirical investigation will be necessary for its discovery. However, let us imagine that B and C differ in their chemical composition, but in each case there is some component with enough vacant positions in its outer shell of electrons to allow A-particles to make bonds. We need be no more specific than this, for only this property is relevant for the disposition, and the inclusion of irrelevant properties may make us feel obliged to give up type-type identities. It may be thought that the categorical property which we correlate with the disposition is hopelessly vague; but on the contrary, such vagueness is a virtue. A disposition term such as 'breakability' is itself a vague term, and we are entitled to offer a categorical correlate of equal broadness,' for instance, 'consisting of structural bondings too weak to withstand pressures above degree f' (call this c,). Many different substances may have such 'weak bondings', but what substances they are O The Editors of 7ht Philosophical Q u r L n ~ ,1994.
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is irrelevant to the object's breakability; the one property it must have, if it is breakable, is c,. The more we narrow down the vagueness of the disposition term, however, the more we can be expected to sharpen the property term of its categorical correlate. With each disposition we follow this same method in our reasoning. We identify the disposition only with those properties relevant to its determination. In this way type-type identities could be preserved, so I shall not multiply examples any further. Obviously this method falls well short of a proof of the type-type identities I advocate. I shall say more in favour of such identities later, but it should be noted that such identities are recommended only in virtue of being the most plausible solution to our problem.
2.
Objections to Identip. It may be argued, by the supporters of super-
venience, that as supervenience clearly does hold between the categorical and dispositional, the argument has gone wrong somewhere .- and where it has gone wrong is in the identification of dispositions with their bases. Prior, Pargetter and Jackson give three arguments for distinctness. I shall take the three in turn. The first argument is that we cannot identify dispositional and categorical properties, because dispositions can have different bases in different objects or substances. I hope it is now clear how this objection is to be answered: we deny that dispositions can have different bases. They only have the appearance of permitting different bases through admission of irrelevant properties into the alleged base, which is clearly not what is intended by a base of a disposition. Second, even if we can identify a categorical property c,, present whenever a disposition dl is present, it is argued that we still cannot identify c, and dl because of the possibility that something may possess c, but not dl because it also possesses a property c, which 'swamps' the effect of c,. If such a 'swamping' property is possible then the categorical correlate with which we type-identify our disposition must be one which excludes c,. We could, for instance, submit a wineglass to heat treatment so as to make it considerably less fragile; but in doing so we do not add another (c,) property to its c, property that is the candidate categorical correlate of fragility. Rather, the case is that c, and c, are incompatible properties and in gaining c,, c, must be lost. c, consists of all propertie$ relevant to breaking upon a relatively slight impact. Thus a necessary condition of c, is not-c,. Therefore the second argument is no real threat to identity. O The Editors of 7he Pkilosophkd QuorLerP, 1994
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We now come to the most serious argument offered by Prior, Pargetter and Jackson. Property names are rigid designators, so if fragility is identical with c,, it is so necessarily, i.e., at all possible worlds. But there are possible worlds where fragility is not identical to c,; therefore 'fragility = c,' is a necessary falsehood, i.e., false at all possible worlds, including the actual world. This argument trades on the seemingly undeniable fact that it is contingent what the 'base' or categorical correlate of a disposition is. This argument can be countered, however, by observing that the authors commit a surprising mistake. It is surprising because Elizabeth Prior accuses A.D. Smith of a very similar error." The error is this. An object may be non-fragile in our world - call this property 'nonfragility,'. It may be the case that if we transport the object to another possible world - let us call it Neptune, purely for convenience - it breaks there upon the slightest of impacts. Does this mean that the object is now fragile, as A.D. Smith suggests? In a sense it is, but not in a sense opposed to non-fragility,. If it were fragile in a sense opposed to non-fragility, then we would have a very curious situation, for a disposition would have been gained, and another lost, solely by removal to a different location. But an object's dispositional properties are surely intrinsic, and its environment is not to be included in the bases of its dispositions. We can avoid the odd result if we insist that dispositions are not held relative to location: all that an environment can do is encourage or hinder the man$station of a disposition, not determine the possession of the disposition itself. Let us re-examine the objection. The essential contention that does the important work is that 'there are worlds where fragile objects do not have ... [c, - the putative base property to which fragility is allegedly identical], for it is contingent as to what the basis of a disposition is'. Certainly I did commit the identity account to the thesis that disposition-categorical property identities are a posteriori, but does this mean they are contingent? If so then there are possible worlds where the identity does not hold. Such identities are contingent, I hold, but only in so far as the laws of nature and environmental conditions, which are at work in the manifestation of a disposition, are contingent. Given a set of laws and a set of environmental conditions, and given a specification of a categorical property,. then dispositions are physically necessitated. Hence the following analysis is possible, and more plausible than that of the Prior I'
See Prior, AJP 1981; Smith, Mind 1977
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et al. objection. All our disposition ascriptions are Earth-relative, that is, relative to our operative, contingent, laws of nature and background conditions. Thus when we speak of fragility and non-fragility we refer to Earth-bound dispositions fragility, and non-fragility,, and such properties can be type-identical to specific categorical properties. It could be, however, that an object which is non-fragile, would break easily at Neptune. An object which breaks easily at Neptune does not necessarily have the disposition fragility,, but may have a different disposition, fragility,, if laws or conditions differ at that world; of course, there is the possibility that the conditions and laws at another world coincide with our own. In this case, fragility, and non-fragility, are not mutually exclusive; something could be both fragile, and non-fragile, at the same time. We can say, therefore, that if fragility, is type-identical with c, at our world, then it is so at all possible worlds. Consider now the trans-world disposition ascription: x may have the property c, which is identical with fragility,. Locate x at a possible world w, where conditions are such that no manifestation of this disposition is possible. This does not mean that the disposition to break easily at Earth is lost, just as c, is not lost; thus trans-world disposition ascriptions are no objection to type-type identities. Fragility, is identical with c, at all possible worlds, even those which make its manifestation impossible. VI. REDUCTION AGAIN
It is now time to develop some of the implications of the argument. I have made the following claims:
1. Identifjnng dispositional and categorical properties is, on its own, neutral as to which are the 'real' properties, i.e., it is neutral between dispositional monism and categorical monism. 2. Both dispositional and categorical monism make ontologically reductive claims that certain concepts do not refer to real properties. Categorical monism states, for instance, that categorical properties are the 'real' properties and dispositional properties are not, and hence that all dispositional terms are to be reduced to categorical property terms. 3. An identity relation between the dispositional and the categorical would b e insufficient for an ontological reduction, for identity is a symmetrical relation, whereas ontological reduction, if it is to mean anything at all, must be a n asymmetrical relation. We O The Rditors of 7he Philosophical (Luor!m&, 1994.
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must therefore analyse reduction into two individually necessary and (possibly) jointly sufficient conditions: (a) co-extension of the reduced and reducing terms, and (b) supervenience of the reduced on the reducing terms. 4. Supervenience can be understood in various ways, but essentially supervenience must, if it is to have any significance, be an asymmetrical relation so that the subvenient and supervenient can be distinguished. We can explicate the relation in terms of subvenient properties 'fixing' the supervenient properties. 5. Supervenience within identity is quickly exposed as an empty concept, however. We can make a case for type-type identities between dispositional and categorical properties, in which case the alleged 'fixing' relation could go either way. If asymmetry cannot be maintained, then supervenience holds in neither direction. 6. Therefore, the dispositional is not reducible to the categorical, nor is the opposite true. My argument can be stated simply. If two things, such as properties or events, are identical, then supervenience is out of the question, for it requires the subvenient and supervenient to be distinct. If we are looking for an ontological reduction, then we must hold the absurd position that something can supervene upon itself. The notion of an ontological reduction comes out of two conflicting desires: to say that two things are actually identical, but then to say that one of them exists while the other does not. Such a conjunction is impossible, for we are concerned with two co-extensive terms, not two entities. Hence all that can really be reduced is terms or predicates, and only here where they have co-extensive reference. Reductionists cannot, therefore, have the sort of reduction they want. A categorical monism like Quine's becomes, on this argument, an incoherent position. If a disposition just is a particular state or mechanism, then we cannot say that the categorical property exists but the dispositional property does not, for the two are admitted to be a single thing. Thus all that Quine could hope to reduce is disposition terms, which would fail to give the ontological primacy to the categorical which categorical monism claims. A reduction of disposition terms is not even possible, though. Given type-type identities, to which Quine assents, no asymmetry of 'fixing', in the sense I have explained, exists for terms. Quine's thesis can, at best, be interpreted as saying something (false) about two forms of discourse, not as saying anything about ontology. At O The Editors of 7he Philosophical Qumfnb, 1994.
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best it is therefore a far weaker thesis than may at first appear. At worst, it makes an incoherent ontological claim. A further corollary should be mentioned. I have spoken of identities between dispositions and their 'putative bases'. We can now see why 'putative base' needs to be taken with a pinch of salt. 'Base' gives the suggestion that one property is the primary determiner or fixer of a disposition. If such determining goes both ways, then neither category of property can claim primacy so as to be 'base' properties of another category. It must therefore be regarded as ontological prejudice to speak of categorical bases of dispositions. We might just as well speak of dispositional bases of categorical properties, but better still we can drop the notion of anything 'basing' a property to which it holds a relation of identity. What of philosophy of mind: is reduction possible here? One important question in philosophy of mind is whether we make type-type or token-token identifications between the mental and the physical. If like David Lewis we opt for type-type identifications, then reduction is not possible. Such an ontology suggests that a single event is describable in both mental and physical terms. Reduction, if it is to be considered at all, can concern only these terms, not the events themselves. I have shown that a certain sense of reduction - that of an ontological reduction between identicals - is empty. Is there any respectable use for the notion of reduction? Likewise, what are the acceptable uses of supervenience? I deem the following uses to be acceptable: 1. a can supervene upon b when a and b are not identicals, as where Plato's writing dialogues supervenes upon the death of Socrates. However, as a and b are not identical, reduction is out of the question. 2. Reduction and supervenience, taken as epistemological or logical notions, are respectable, though they indicate nothing about ontology (that is, nothing more than the identity relation indicates). The epistemological notion, for instance, concerns the perspicuity of our explanations. It may lead us to try to reduce our concepts to simple conceptual systems, as Harri: (1972 p. 141) suggests; for example, we minimize the number of basic terms in our conceptual system when we reduce to three types the number of basic units composing all the atoms. It may.just be that we find terms of one class more 'epistemologically accessible'. For instance, if the property which d and c both 6 The Editors of 7he Philosophical Quorlnly, 1994
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denote causes x to change, this change may be more easily explained in C-terms rather than D-terms. Ontologically speaking, it would be correct to say both that d and c are causes of the change, but epistemologically we may prefer an explanation in terms of c. Nagel suggests a reduction in such circumstances, a reduction of the kind where we translate terms of one class into terms of a class we find more explanatory. Regarding dispositions, it may be more epistemologically accessible to explain changes in dispositional properties in terms of changes in categorical properties, but any objection to explaining categorical changes in terms of dispositions can only be pragmatic, thus revealing nothing about ontology.l2
REFERENCES Armstrong, D.M. 1968: A Materialist 77zeoly ofthe Mind (London: Routledge). Charles, D. 1992: 'Supervenience, Composition, and Physicalism', in Charles and Lennon, pp. 265-96. Charles, D. and Lennon, K. (eds) 1992: Reduction, Explanation and Realism (Oxford: Clarendon Press). Churchland, P.M. 1984: Matter and Consciousness (Cambridge, Mass.: MIT Press). Davidson, D. 1970: 'Mental Events', in Essays on Actions and Events (Oxford UP), pp. 207-25. Fodor, J.A. 1974: 'Special Sciences, or the Disunity of Science as a Working Hypothesis', Synthese 28, pp. 97-1 15. Griffin, J. 1992: 'Values: Reduction, Supervenience, and Explanation by Ascent', in Charles and Lennon, pp. 297-322. Harrt., R. 1964: Matter and Method (London: Macmillan). -1972: 77ze Philosophies ofSciace (Oxford UP). Horgan, T. 1982: 'Supervenience and Microphysics', Pm$c Philosophical Quarter& 63, pp. 29-43. Kim, J. 1978: 'Supervenience and Nomological Incommensurables', American Philosophical Qarter& 15, pp. 149-56. - 1984: 'Supervenience and Supervenient Causation', Southem .Tournal of Philosophy 22, pp. 45-56: Lewis, D. 1980: 'Mad Pain and Martian Pain', in N. Block (ed.), Readigs in Philosophy of Psychology, Vol. I (London: Methuen), pp. 216-22. Lewis, H.A. 1985: 'Is the Mental Supervenient on the Physical?', in B. Vermazen and M. Hintikka (eds), Essays on Dauzdron: Actions and Events (Oxford: Clarendon Press), pp. 159-72. Mackie, J.L. 1973: Truth, ProbabiliQ and Paradox (Oxford UP). Mumford, S.D. 1995: 'Dispositions, Bases, Overdetermination and Identities', Ratio 8, forthcpming. -
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12 My thanks to Robin Le Poidevin and a referee for 7he Philosophical &a&& for comments on earlier versions of this paper. I also thank Harry Lewis for the discussions which prompted this work.
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Nagel, E. 1961: 'The Structure of Science (London: Routledge & Kegan Paul). Papineau, D. 1990: 'Why Supervenience?', Anabsis 50, pp. 66-7 1. Peacocke, C. 1978: Holistic Explanation (Oxford: Clarendon Press). Prior, E.W. 1981: 'Smith on Dispositions', Australasian Journal of Philosophy 59, pp. 206-10. --- 1985: positions (Aberdeen UP). Prior, E., Pargetter, R. and Jackson, F. 1982: 'Three Theses about Dispositions', American Philosophical Quzrt~b19, pp. 25 1-7. Quine, W.V. 1974: ?he Roots ofRejirence (La Salle: Open Court). Smith, A.D. 1977: 'Dispositional Properties', Mind 86, pp. 439-45. Smith, P. 1992: 'Modest Reductions and the Unity of Science', in Charles and Lennon, pp. 19-43. Stich, S. 1978: 'Autonomous Psychology and the Belief-Desire Thesis', Monist 61, pp. 573-91. Teller, P. 1983: 'A Poor Man's Guide to Supervenience and Determination', Southern Journal OfPhilosophy, Suppl. Vol. 22, pp. 137-62.
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