13b. humphreys (1997) - how properties emerge

8/14/2019 13b. Humphreys (1997) - How Properties Emerge

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How Properties EmergeAuthor(s): Paul Humphreys

Reviewed work(s):Source: Philosophy of Science, Vol. 64, No. 1 (Mar., 1997), pp. 1-17Published by: The University of Chicago Presson behalf of the Philosophy of Science AssociationStable URL: http://www.jstor.org/stable/188367.

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How PropertiesEmerge*Paul Humphreyst$

Departmentf Philosophy,University f Virginia

A framework or representing specifickind of emergentproperty nstance s given.Asolution to a generalizedversion of the exclusionargument s then providedand it isshown that upwardsand downwards causation is unproblematical or that kind ofemergence.One real example of this kind of emergence s brieflydescribed and thesuggestionmade that emergencemay be more common than currentopinionsallow.

1. Introduction.Lurkingin the shadows of contemporaryphilosophyof mind is an argument widely believedto produceseriousproblemsfor mental causation.This argumenthas variousversions,but onepar-ticularlystarkformulation s this:(1) If an eventx is causallysufficient or an eventy, then no event

x* distinct from x is causallyrelevantto y (exclusion).(2) For every physical event y, some physical event x is causallysufficient or y (physicaldeterminism).(3) For every physical event x and mental event x*, x is distinctfrom x* (dualism).*ReceivedMarch 1996;revisedSeptember1996.tSend reprintrequests o the author. CorcoranDepartmentof Philosophy,521 CabellHall. Universityof Virginia,Charlottesville.VA 22903.$Previousversions of thispaperwerereadat VirginiaPolytechnicInstitute,Duke Uni-versity.The Universityof Virginia, he Universityof Pittsburgh, he BritishSocietyforthe Philosophyof Science,and an IUHPS meetingin Warsaw.Commentsandsugges-tionsfromthose audiencesand the two anonymousreferees romPhilosophyof Sciencewere very helpful in improvingthe paper. I am also gratefulfor conversations andcorrespondencewithRobertAlmeder,JamesBogen,RichardBurian,JohnForge,Da-vid Henderson,MartinJones,JaegwonKim,JamesKlagge,KenOlson,FritzRohrlich,and Abner Shimony.Research for this paperwas conductedpartlyunderNSF grantSBR-9311982and the supportis gratefullyacknowledged.Philosophy of Science, 64 (March 1997) pp. 1-17. 0031-8248/97/6401-0001$2.00Copyright 1997 by the Philosophy of Science Association. All rights reserved.

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PAUL HUMPHREYS(4) So: for everyphysicalevent y, no mental event x* is causallyrelevant to y (epiphenomenalism). Yablo 1992,247-248).1

This exclusionargument,as it is usuallycalled,has devastatingcon-sequencesfor any position that considersmentalproperties o be real,includingthose non-reductiveviewsthat supposementalproperties osuperveneupon physicalproperties.For if mentalpropertiesarecaus-ally impotentvis-a-visphysicalproperties, he traditionalworryaboutepiphenomenalismconfronts us: What is the point of having them inour ontology if they are idle? Abstract objects escape this worry, forwe do not expect them to do causal work, but mental propertiesareretainedin part because we believe them to affect the course of theworld. If the exclusion argument s sound, then ratiocination,qualia,and the hopes and fears of mankind are simply smoke on the fire ofbrainprocesses.This is badenough,but thereis a secondargument,devisedby Jaeg-won Kim, that in conjunctionwith the exclusion argumentseems torendernonreductivephysicalismnot merelyuncomfortablebutunten-able, for it has as a conclusion that nonreductivephysicalism s com-mitted to the view that some mental propertiesmust cause physicalproperties.Kim'sargument,whichI shallcall the downwardsausationargumentwas originallylevelledagainstboth nonreductiveand emer-gentistapproaches:

Butwhyareemergentismand nonreductivephysicalism ommittedto downwardcausation,causationfrom themental to thephysical?Here is a brief argumentthat shows why. At this point we knowthat, on emergentism,mental propertiesmust have novel causalpowers. Now, these powersmust manifest themselvesby causingeitherphysicalpropertiesor other mentalproperties.If theformer,that already is downward causation. Assume then that mentalpropertyM causes another mentalpropertyM*. I shall showthatthis is possible only if M causes some physical property.Noticefirst that M* is an emergent; his means that M* is instantiatedona given occasion only because a certainphysical propertyP*, itsemergencebase, is instantiated on that occasion. In view of M*'semergentdependenceon P*, then,what are we to think of its causaldependenceon M? I believe that these two claimsconcerningwhyM* is present on this occasion must be reconciled,and that theonly viable way of accomplishing t is to suppose that M caused1. See Yablo 1992,247, fn. 5 for a partiallist of versions of this argument hat haveappeared n the philosophical iterature. note here thathe doesnot endorsethesimpleversion of the exclusionargumentbecause it is unsound.

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HOW PROPERTIES EMERGEM* by causing its emergence base P*. In general, the principleinvolved here is this: the only way to cause an emergentproperty tobe instantiated is by causing its emergence base property to be in-stantiated.And this means that the same-level causation of anemergent property presupposes the downward causation of itsemergentbase. That brieflyis why emergentism s committed todownward causation. I believe that this argumentremainsplausi-ble when emergence s replaced by physical realization at appro-priateplaces. (Kim 1992, 136)

Conjointhis secondargumentwiththefirst,andyou have more thanmere trouble for nonreductivephysicalismandemergentism,you havecontradictoryconclusions.(4) entails that there is no downwardscau-sation from the mental to the physical;the downwards causation ar-gumentconcludes that nonreductivephysicalismand emergentism e-quiresuch downwardscausation.Something must go if mental propertiesare to survive, and thatsomething is both arguments.Much is wrong with the exclusion ar-gument,but what it shareswith the downwardcausationargument sa pinched commitment to a dualist ontology, a laudable but usuallyunargued allegianceto the causal closure of the physical realm, and(nowadays)the idea that supervenience s the right way to representthe relation between the lower and higherlevels of the world'sontol-ogy. Each of these is popularand each is wrong.2. A WiderPerspective.The firstthing to note about these argumentsis that they are extremely general-they do not seem to rely on any-thing that is characteristicof mentalproperties,suchas intentionality,lackof spatial ocation,havingsemanticcontent,and so on, and indeedit is often mentionedin passingthat the argumentscan be generalizedto apply to a hierarchicallyordered set of properties,each level ofwhich is distinct fromeveryother level.2 f the exclusionargumentdoesgeneralizeto such hierarchies,and if, for example,chemicaland bio-logical events occupy higher levels than do physical events, then nochemical or biological event could ever causally influence a physicalevent, and if both argumentsso generalize,then nonreductivephysi-calismleadsto inconsistencieswhenappliedto thegeneralrealmof thenatural sciencestoo.

The situationis in fact more extremethan this, because most of ourphysicalontology lies above the most fundamental evel, and in con-sequenceonly the most basic physical propertiescan be causallyeffi-2. See, e.g., Yablo 1992, 247, fn 5.

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PAUL HUMPHREYScacious if these argumentsarecorrect.Indeed,unless we have alreadyisolated at least some of the most fundamentalphysical properties,every single one of our causal claims within contemporaryphysics isfalse and consequentlythere are at presentno true physical explana-tions that are groundedin causes.All of these are,of course,surprisingand unwelcomeconsequences.We tend to believe that currentelementaryparticlephysics does reli-ably describethe formative nfluenceson ourworld,that chemicalcor-rosion can cause the physicalfailure of an aircraftwing, and that thegrowthof a tree can causechangesin the ground temperaturebeneathit. Yet our beliefs on this scoremay well be wrong. Perhapsthecorrectformulation of physicalism s a strict one: if, as manyhold, everythingis composedof elementaryparticlesor fields,and the laws that governthose objects ultimatelydetermineall else that happens,then there arefundamentalphysical events that are causally sufficient for aircraftwing failures, changes in soil temperatures,and all other physicalevents. This is a positionthatrequires eriousconsideration,and indeedthose versionsof physicalismthat requireall non-physicalphenomenato supervene upon physical phenomena can be easily and naturallyadaptedto this kind of strictposition. So we need to examinein detaila generalizedversion of eachargument o see whether his radicalphys-icalist conclusioncan be supportedandwhetherthe problemsfor non-reductivephysicalismextendall theway down to the penultimate evel.Thereis a second reason for generalizing he arguments.It is pref-erable to examine argumentsin a form in which the contextual as-sumptionsare as transparentas possible.The relation betweenmolec-ular chemistryand physics, say, is much more easily assessed than isthe relation betweenphysics and psychology becausewe have clearlyarticulatedtheories for the firstpair, togetherwith a reasonablyclearset of constraintson the degreeof reducibilityof molecularchemistryto particlephysics,but those relations are muchmurkier n the case ofphysics and psychology. In addition, by focusing on the lower levelsof the hierarchy,we can avoid difficultproblemsinvolvingthe mentalthat are here irrelevantsimply by recastingthe argumentsin a formthat avoids reference o specificallymentalproperties.3To generatethe general arguments,we need a hierarchyof levels.For present purposes, I shall simply accept that this can be done in3. Thisallows,of course,that the realm of the mental doesgenerateadditionalpeculiarproblems.The exclusionand downwardscausationargumentsareentirely ndependentof thosepeculiarities,however,except perhaps or a prejudiceagainstthe mental.Wereit not for that prejudice,the exclusion argumentcould be run in reverse to excludephysicalcauses,a featureemphasized o me by PeterDlugos.

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HOW PROPERTIES EMERGEwhateverway the reader finds most congenial. (The strata must cor-respondto some real differences n ontological levels rather than to amere set of epistemicdistinctions.)For concreteness,we can think interms of this assumption: L)There s a hierarchyof levels of propertiesL0,L1,... L,, . . . of whichat least one distinct evelis associatedwiththe subjectmatter of each specialscience,and Ljcannot be reducedtoLi for any i < j.I shallnot try here to give any additional criteria or distinguishinglevels.Rather,I am simply adopting,for thepurposesof theargument,the abstractassumptionof both argumentsthat there is indeed somesuch hierarchy.At the very least, one would have to considerthis anidealization of some kind, and we shall see that the assumptionthatthere is a discretehierarchyof levels is seriouslymisleadingandprob-ably false. It seems more likely that even if the orderingon the com-plexity of structuresrangingfromthose of elementaryphysicsto thoseof astrophysicsand neurophysiologyis discrete, the interactions be-tween such structures will be so entangled that any separationintolevels will be quite arbitrary.3. TheGeneralizedExclusionArgument.As a generalprinciple,premise(1) is false as we originallyformulated t, for it assertsthat, first,causalantecedents of x and, second, events causally intermediatebetweenxand y are causallyirrelevant o y, and this is obviously wrong.So, let us use the preliminarydefinition:An eventz is causallyconnected o a second event x if and only if xcausesz or z causesx. z is causallydisconnectedromx just in casez isnot causallyconnectedto x, The properformulationof (1) is then:

(1') If an eventx is causallysufficient or an eventy, thenno eventx* distinctfrom x and causallydisconnected romx is causallyrelevant to y. (exclusion)4

To make the revisedprincipletrue requiresa strictcriterion of eventidentityso that in particular, he exact time and way in which an eventoccurs is crucial to that eventhavingthe identityit does. This criterionis needed to exclude cases wherex is sufficientfor y but x*, which iscausally disconnectedfrom x, bringsabout (a somewhat earlierana-logue of) y beforethe connectingprocessfromx has broughtabouty.4. I am here setting aside overdetermining vents as genuineexamplesof causation.Although some discussionsof the exclusionargumentsee acceptanceof overdetermi-nation as a way out of the difficulty,this is not a convincingmove, and I shall notfollow that route. Not the least reasonfor this is that casesof simultaneousoverdeter-minationare exceedinglyrare.

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PAUL HUMPHREYSSuch a strictcriterion,called 'fragility'by David Lewis,5 s controver-sial,andrightlyso, butI shallacceptit heresimplybecause tsadoptionavoids distractingissues and does not affect the essential features ofthe argument.Supposenow that we accept principle(L) and ask whether an ana-logue of premise(2) is plausiblefor each level L. What I shall call i-determinism whichis what a generalizationof (2) asserts) s differentfrom i-closure,the thesis that all events that arecausallyrelevantto agiven i-level event are themselves -level events: i-determinism s com-patible both with upwardsand with downwardscausation,whereani-level event causes another i-level event through a chain involvingevents at other levels. To see that (2) is not true when generalized,consider(2) with 'physical'replacedwith 'biological'.It mightnow betrue that for everyfuturebiological event there is some biologicalan-tecedent that guaranteesit. But to assert biological determinism orevery biological event in the history of the universe would be to ruleout what is commonly believed, which is that biological phenomenawere not always present duringthe developmentof the universe.6Thefirstbiological event, underwhatevercriterionof 'biological'you sub-scribeto, musthave had a non-biologicalcause. So a generalizationof(2) is not plausiblefor any level above the most fundamental evel ofall, which we call the O-level,and so we shall restrict ourselves to aformulationof (2) for that level only, the level of whateverconstitutesthe most fundamentalphysical properties,viz..

(2') For everyO-levelevent y, some O-levelevent x is causallysuf-ficient for y. (O-leveldeterminism)7The third premiserequiresa criterion of distinctness of events (as

does (1')). This cannot be done in terms of spatiotemporaldistinctness5. See Lewis1986,PostscriptE. Lewisrejectsextremeversionsof thefragilityapproach.6. This temporaldevelopmentgivesrise to evolutionaryemergence.I shall not pursuethat topic here but the readercan easilydevelopsuch an account from materials n thispaper.7. Premise 2') is, on currentevidence,false becausefundamentalphysics appears o beindeterministicn certainrespects.I have preserved he originalform of the argumentto keep things simple,but to allay worriesabout the truth status of (2'), one can re-formulatethe argument husly:Replace causallysufficient n (1') and (2') by caus-ally complete, event by set of events, and x by {xi}, where causallycompletemeans either that all eventsnecessary n the circumstancesor y are included n the setor that all events that areprobabilistically elevantto y are in the set. See, e.g., Lewis1986for one accountof the former,Humphreys1989 for one account of the latter.(3),(4) remain as they are. (2') will be false if the universehad a first uncausedevent,butthat fact is irrelevanthere.

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HOW PROPERTIES EMERGEalone, because on supervenienceaccountsthe supervening ventis spa-tiotemporarycoincidentwith the subvenientevent(s).So the burdenofcharacterizingdistinctivenesswill have to lie on principle (L) and weshall take as a sufficient condition for two events being distinct thatthey occupy different levels in the hierarchy.With this understandingwe have:

(3') For every0-level eventx and everyi-level eventx* (i > 0) x isdistinct from x*, (pluralism)Then it follows immediately hat:

(4') For every 0-level event y, no i-level event x* (i > 0) that iscausallydisconnectedfrom every0-leveleventantecedent o yis causallyrelevantto y.This modifiedconclusion shows how nonreductivephysicalismcanavoid the conclusion of the simpleversion of the exclusionargumentand hence can also avoid the overall contradictionwith the conclusionof the secondargument,because the conclusion(4') allowshigher evelevents to causallyaffect 0-level events if the formerarepart of causal

chains that begin and end at the 0-level.8In order for us to use thatpossibility to argue for emergentproperties,we need to addressthesecond argument,which amongst other things, precludeshigherlevelcausal chains that do not involve 0-levelevents.4. Generalizations f the DownwardsCausationArgument. n lookingat generalizationsof the downwardscausationargument, t is worth-while to again lay out explicitlythe assumptionswhichunderlie t. Thefirst is a supervenienceassumptionthat permeatesthe contemporaryliteratureon nonreductivephysicalismand is retainedby Kimfor emer-gent properties.9

(5) Every emergent property is supervenient upon some set ofphysical properties.One naturalgeneralizationof this is:

(5') Everyj-level property(j > 0) is supervenientupon some set ofi-levelproperties, or i < j.8. More complex versions of the argumentobviously allow similarpossibilitiesforcausalchainsbeginningand endingat higher evels than 0.9. Kim actuallyexamines both the realizabilityand the supervenienceapproaches.Irestrictmyselfto the latter.

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PAUL HUMPHREYSStrictphysicalistsmightwant to insist that allhigher evelpropertiessuperveneupon O-levelproperties.However,unlike the firstargument,

where premise (2) was true only for O-levelproperties,here we canmaintainfull generality.In fact, if there are emergent properties,thestrictphysicalistposition will be false, and we shallhave to leave roomfor some (non-emergent)properties o superveneuponj-level emergentpropertiesbut not upon O-levelpropertiesalone.Next, the assumptionexplicitlycited by Kim:(6) The only way to causean emergentproperty o be instantiatedis by causing its (set of) emergencebase propertiesto be in-stantiated.

Its generalizationwill be (assuming hat superveniences a transitiverelation):(6') The only way to cause a j-level propertyto be instantiated sby causing a set of i-level properties(i < j), the subvenientbasis, to be instantiated.

Premises(5') and (6') are closely related, for the plausibilityof (6')rests on accepting something like (5'), the idea being that emergentpropertiescannot exist separatelyfrom whateverphysical propertiesgive rise to them.Then we have the importantcondition:

(7) A property s emergentonly if it has novel causalpowers10We can retain this unchangedfor the generalizedargument.5. An EmergentistAnswerto the SecondArgument.How can we nowescape the conclusion of the downwardscausationargument?We canbegin by refiningthe event ontology used in the argument,which ap-peals to propertiesas causes. This way of speaking, about propertycausation, is clearly an abbreviationfor an instance of one propertycausingan instance of anotherproperty.We shall have to resort hereto a certain amount of notational clutter. This will not be pretty,butit has a certainsuggestiveness hatmay be helpful.Fromhereon I shalltalk of i-levelpropertiesand entities,Pi andxi, respectively, or i - 0.I call a property(entity)an i-levelproperty (entity)if i is the first level10. In fact, as MartinJonespointedout to me (pers. comm.), the noveltyof the causalpowers seems to play no role in Kim's central argument.Even if mental propertiesproducedfamiliarphysical consequences hat could also be broughtabout by physicalproperties, he argumentwould still hold. The use of noveltyis primarily n character-izingthe differencebetweenemergentandnonemergentproperties, or it is an essentialfeatureof emergentproperties hat they be new.

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HOW PROPERTIES EMERGEat which instances of Pm(xi) occur. i-level propertiesmay, of course,also have instances at higherlevelsas for example,physical propertiessuch as mass and volume, do. We need to keep distincti-levelentitiesand i-level properties,for it is possible that, in general,i-level entitiesmay possessj-levelproperties, or i ? j. However,for simplicity nwhatfollows we shall assume that i-levelpropertiesareinstantiatedbyi-levelentities. So we have that Pi(xi)(tl) causes Pi(xi)(t2) where t2 > t, andxi, xi, the entities possessing the properties, may or may not be thesame.'1Here Pi is the mth i-level property;xi is the rth i-level entity,and Pi(xr)(tk) denotes the instantiation of Pi by xi at time tk.Suppose now that the i-level properties constitute a set I =P ..... . .. .2 and that these i-levelpropertiesarecompletein thesense that I is exhaustive of all the i-levelproperties.Now introduceafusion operation .*.], such thatifP(xi)(tl), Pn(xi)(tl)are i-levelpropertyinstances,then [Pi(xi)(tl)*Pi(xi)(t)]is an i + I-levelproperty nstance,the result of fusing Pm(xr)(tl)and Pn(xi)(t,). I want to emphasizeherethat it is the fusion operation on the propertyinstances that has therealimportance or emergence.Usually, the fusionoperationactingonobjectswill merelyresultin a simpleconcatenationof the objects,hererepresentedby [(xi) + (xi)],withinwhich the individualsxi and xi retaintheir identities. However, as we noted earlier, for full generalitywe would need to allow for the possibility of new i + I-level ob-jects.'3Moreover,fusion usually is not instantaneous,and we shouldrepresent that fact. So I shall represent the action of fusion by[pi(xi(tl)*Pn(xs)(t,)] = [Pm*Pi][(xi) + (xi)](t1).4 For simplicity,I shallassumeherethat * itself is an i-leveloperation (i.e., that it is an opera-tion of the samelevel as the property nstanceswhich it fuses.)11. Kim asserts(1992, 123)that the emergentistsof the 1920s held thatno new entitiesemergedat new levels of the hierarchy,only new properties.Allowing that to be his-toricallyaccurate, t is as well to allow, at least notationally,that we might have newentitiesemergingas well as properties.12. The cardinalityof this set is unrestricted-the integer subscriptsare used for con-venienceonly.13.Supervenience dvocateshavealso recognized he need for this. See,e.g., Kim 1988.14. Thereis a notationallyharmlessbut metaphysically mportantambiguityherebe-tween fusion operationson propertyinstancesand on properties.The latteris meta-physicallyderivative romthe former n that when[Pi(xi)(ti)*Pi(xi)(tl)]xists,then thereis by virtueof this an instanceof a novel property,signifiedby Pm*Pn,t level i + 1.This disambiguationsits most happilywith the position that fusion bringsinto beingnewproperties,a positionthat seems to fit well with the idea of emergence.Those whosubscribe o the view thatthere are eternalemergentproperties hat areuninstantiatedprior to some time can think of Pm*Pnas a mere notational device indicatinga moveto a previouslyuninstantiatedpropertyat a higher evel.

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PAUL HUMPHREYSBy a fusion operation, I mean a real physical operation, and not amathematical or logical operation onpredicative representations of prop-

erties. That is, * is neither a logical operation such as conjunctionordisjunctionnor a mathematicaloperation such as set formation.15need not be a causal interaction,for it can represent nteractions ofquite differentkinds.The key feature of [Pi*Pi][(x) + (xi)](t) is that it is a unifiedwholein the sense that its causal effects cannot be correctly represented nterms of the separatecausal effectsof Pi(xi)(tl) and of Pi(xi)(t). More-over, within the fusion [Pi*P ][(xi) + (xi)](t) the originalproperty n-stancesPi(xi)(tQ),Pi(xi)(tl)no longerexist as separateentities andtheydo not have all of their i-level causal powers available for use at the(i + l)st level.16Some of them, so to speak, have been 'used up' informingthe fused propertyinstance.Hence, these i-level property n-stances no longer have an independentexistence within the fusion. Inthe course of fusing they become the i + I-level propertyinstance,ratherthan realizingthe i + I-level propertyin the way that super-venience theorists allow the subvenientproperty nstances to continueto exist at the same time as the supervenientpropertyinstance. Forexample,thecuspedpanellingandbrattishing hat makes the fan vault-ing of the King's College chapelarchitecturally ranscendentexists si-multaneouslywith the supervenientaestheticgloriesof that ceiling.Incontrast,whenemergenceoccurs,the lower levelproperty nstancesgoout of existencein producingthe higherlevelemergent nstances.Thisis why supervenienceapproacheshave great difficulty n properlyrep-resenting emergenteffects. To see this, consider the following formu-lation of strongsupervenience:17

A strongly supervenesupon B just in case, necessarily,for each xand each propertyF in A, if x has F, then there is a propertyG inB such that x has G and necessarily f any y has G, it has F. (Kim1984, 165)Now let A be the fusion [Pi*Pi][(xi) + (xs)](t). Upon what can this

15. In contrast,it is standard n the literatureon supervenienceo construethe subven-ient basis in terms of sets of properties,or in terms of a disjunctivenormal form ofproperties,where it is assumedthat it makes sense to perform logical operationsonproperties.These devicesareinappropriateor characterizing mergentpropertiesandare a legacyof the continuingbut, in myview,fruitlessattemptto reconstruct ausationand associatedconcepts logicallyratherthan ontologically.16. As mentionedearlier,the objectsthemselveswill often retain theirseparate denti-ties.17. This argumentcarriesover, with simplemodifications,to the definition of weaksupervenience.

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HOW PROPERTIES MERGEsupervene?Because we are hereconsideringonly the abstractpossibil-ity of emergent features, consider a very simple world in whichPi(xi)(tl) andPi(xi)(tl)are the only i-levelproperty nstancesoccurringat tl, and in which there are no i-levelpropertyinstancesat tl. Then,trivially,there is nothing at t' at the i-levelupon which [Pm*Pi][(xi)(xi)](tl) can supervene.Faced with this, the supervenienceadvocatecould try a differentstrategy,one that relies on the fact that the defi-nition of strong superveniencedoes not requirethe supervenientandsubvenient instances to be simultaneous. So one could use the earlierinstancesPi(xi)(tl) andPi(xi)(tl)themselvesas the baseuponwhich thelater [Pi*Pi][(xi) + (xi)](t1) upervenes.Yet once one has allowed thistemporalgap, the supervenience elation s in dangerof collapsing ntoan ordinarycausal relation.In orderfor the base instances to (nomo-logically)necessitatethe fusion instance,the absence of all interveningdefeaterswill have to be includedin the subvenientbase, and thiswillgive us a base that looks very much like a Millian unconditionalcause.18Whatever the superveniencerelation might be, the way it isused in nonreductivephysicalismis surely not as a causal relation,because thatwouldimmediatelyconvertnonreductivephysicalismntoold-fashionedepiphenomenalism.

A second reason why supervenienceseems to be an inappropriaterepresentationof certain cases of fusion is given by the physicalex-amplesin Section 6, and I thus refer the reader to that section.How-ever, because my purpose here is not to attack supervenience,butrather o providea solution to theproblemof upwardsanddownwardscausation,I now return to that issue.It has to be said that theunity imposed by fusionmightbe an illusionproducedin all apparentcases by an epistemicdeficit,and that whenproperly representedall chemical properties,for example, might berepresentable n terms of the separable (causal) propertiesof theirchemicalor physicalconstituents. But whetherthis can be done or notis, of course, the issue aroundwhich emergentismrevolvesand I shalladdressit explicitlyin a moment in termsof some examples.What Imaintainhereis this: that one comprehensibleversion of emergentismasserts that at least some i + 1-levelproperty nstancesexist, thattheyare formed by fusion operationsfrom i-level propertyinstances,andthat the i + 1-levelpropertyinstances are not supervenientupon thei-levelproperty nstances.With thisrepresentationof theemergent +1-levelproperty,let us add a claim that is characteristicof many ver-sions of non-reductivephysicalism,especiallythose motivatedbymul-tiple realizability onsiderations; he tokenidentityof i + 1-levelprop-18. See Humphreys1989,Section25, for a discussionof this condition.

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erty instances and fusions of i-level property instances. That is,althoughwe cannot identify the propertyPi+ with [Pi*Pi] when Pil+is multiplyrealizable,we canidentifysome instancesof P+1 with someinstances of [Pi*P]. It is importantto remember or the purposesofthe present argumentthat we areconcernedwith causaland otherin-teractions,and not with the problemof how properties hemselvesarerelatedacross levels. The latteris the focus of greatestconcern withinnonreductivephysicalism,but ourproblemscan be solved without ad-dressing the interlevelrelationshipsof the propertiesthemselves.Infact, given that the higher level propertiesare emergent,there is noreason to identify them with, or to reduce them to, combinationsoflower level properties. Coupled with our previousreminderthat it ispropertyinstances that are involvedin causalrelations,and not prop-erties directly, we now have a solution to the downward causationproblemfor the case of emergentproperties.19Supposethat P+ I(x+ )(t') causesPik+xik+)(t2),whereboth of theseinstancesare at the i + 1-level.What we have is that the i-levelpropertyinstances Pm(xr)(tl) and Pi(xs)(tl) fuse to produce the i + I-levelproperty instance [Pm*Pi][(xi)+ (XS)](tl),which is identical withPi+(x+ 1)(tD). his i + I-levelproperty nstance then causes the secondi + I-level property instance P+ 1(xik+)(t2). his second i + I-levelproperty nstance,if it is also emergent,will be identicalwith,althoughnot result from, a fusion of i-level property instances [Pi*Pj][(xi)+(xv)](t2).But there is no directcausallink fromthe individualpropertyinstancesPm(xr)(tl)and Pi(xi)(tl) to the individualdecomposedprop-erty instancesPi(xi)(t3)and Pi(xi)(t3).Diagrammatically,we then have:

Pi+ (xi+ )(t') -causes-+ lx+ 1)(t)I I

(is identicalwith) (is identicalwith)[Pi*Pi[(xr (x) +]() [Px) + ()](t2)? ,\ ,/ \'

(fuses) (decomposes)Pi(Xir)(tl) Pln(XD)(tl) Pi(X)(t3) Ps(X (t3)19. I want to emphasizehere that what follows is to be construedonly as a represen-tation of the correctrelationshipbetweenemergentpropertyinstances and propertyinstanceson lower levels when causal sequencesare involved. It is not to be construedas an argumentthat in all cases where we have different evels of property nstances,emergentismholds. Supervenience oes have some restricteduses.

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HOW PROPERTIESEMERGEI note here that decomposition does not have to occur. The systemmight stay at the (i + 1)stlevel while it producesfurther(i + 1)-leveleffects.Nor is it necessarythatPi+1be an emergentproperty.When itis not, the identity on the right side of the diagramwill not hold, andthe lower two tiers on the right will be missing. Perhapssome i + 1propertyinstancesareprimitive n this way, but this is doubtfulgivenwhat we know of the evolution of our universe.One further source of concern exists and it relates directly to as-sumption(6') of the downward causationargument.Is it possiblefori + 1-level instances to directly produce other i + 1-level instanceswithout synthesizingthem from lower level instances? These higherlevel instances are usually emergent,and so it might be thought thatthey must themselves be formed by fusion from lower level instancesand not by direct action at the higherlevel. This concern fails to givesufficientcredit to the ontological autonomy of emergentproperty n-stances. Recall that i-level instances no longerexist withini + 1-levelinstances-the higher level instances act as propertyinstance atomseven though they may, under the rightcircumstances,be decomposedinto lower level instances. It is perfectlypossible for an i + 1-levelinstance to be directlytransformednto a different + 1-level nstance(oftenwith the aid of otherproperty nstances)or to directly ransformanother,alreadyexisting,i + 1-levelpropertyinstance(againusuallywith the aid of other propertyinstances.) Simply because the i-levelinstances no longerexist, they can play no role in this causal transfor-mation.We can now see what is wrong with premises (5') and (6'). (5')misrepresents he way in which emergent propertyinstancesare pro-duced, for as we have seen, the relationshipbetween the higherandlower levels is not one of supervenience.A last reply is available tosupervenienceadvocates insisting on the need for relations betweenproperties.If theemergent nstance s producedby a causalinteraction,they can insist that causesrequire aws and that the generality nherentin laws requirespropertiesas well as instances. This is not somethingthat a thoroughgoing ontological approachneeds to accept. Singularcausescan be taken as fundamental,20nd whether or not causal laws(or their statements)can then be formulated n termsof relations be-tweenproperties(predicates)dependsupon the complexityof the partof the world involved. Sometimesthey can be, often they cannot.

We have alreadyseen the problemwith (6'): it is false to say thatthe i-levelproperty nstances co-occurwith the (i + l)st levelpropertyinstance. The formerno longerexist when they fuse to form the latter.20. See Humphreys1989,Section25.

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HOW PROPERTIES EMERGEthat a robustlyontic attitude towardsemergentproperties,rather hanthe more common logical approaches, can give us a sense of whatemergentfeaturesmight be like. Most importantof all, I think, is tostop thinkingof these issues exclusively n terms of mentalproperties,and to look for examplesin more basic sciences.In addition,construingthe arguments n terms of multiple ayersofproperty nstancesremindsus of two things:that therearemany, manylevels of propertiesbetweenthe most fundamentalphysicallevel andthe psychological,and that it is left unacceptablyvaguein much of thephilosophical literaturejust what is meant by 'physical'. Being re-minded of the largevarietyof property evelsbelow the psychological,some of which are arguably emergent,should at least make us awareof the need to be more explicit on that score, and that some of themysteriessurrounding he physical/mental leavageareperhaps he re-sult of an inappropriatedichotomy.

6. FromMetaphysics o Physicsand Back. Thus far, the discussionhasbeen completelyabstract.My intention has been simplyto show howone sort of emergentfeature can avoid variousdifficulties nherent nsupervenience reatments.What we have thus shown is the possibilityof propertyinstancesbeing emergent,free from the difficultiesstem-ming from the exclusion and downwardscausation arguments.Evenif there were no actual examplesof fusion, the account of emergencegiven here would be useful becauseit providesa coherentaccount ofa particularkindof emergence hat is devoidof themysteriesassociatedwith earlierattemptsto explicatethe concept. Thereis, of course,thefurtherquestion of whether our world contains examplesof emergentpropertyinstances. The answer to this is a reasonablyconfident'yes'.I shall here only sketch the form that such examples take, referringinterestedreadersto more detailed sources for a richerdescription.It frequentlyhas been noted that one of the distinctive featuresofquantumstates is the inclusion of non-separablestatesfor compoundsystems, the feature that Schrodinger called quantum entangle-ments. 21That is, the composite systemcan be in a purestate whenthecomponent systemsarenot, and the state of one componentcannotbecompletely specifiedwithout referenceto the state of the other com-ponent. Furthermore, he state of the compound systemdetermines he21. The discussion of nonseparability goes back at least to Schr6dinger 1935.d'Espagnat1965is anotherearlysource and more recent discussions can be found inTeller 1986, Shimony 1987, French 1989,Healey 1991, and d'Espagnat1995, amongmany others.

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PAUL HUMPHREYSstates of the constituents,but not vice versa.22This last fact is exactlythe reverse of what superveniencerequires,which is that the statesofthe constituents of the system determinethe state of the compound,but when the superveningpropertiesare multiplyrealizable,the con-verse does not hold. I believe that the interactions which give rise totheseentangledstates lend themselves o the fusion treatmentdescribedin the earlierpart of this paper, because the essentiallyrelational in-teractionsbetweenthe 'constituents' whichno longercan beseparatelyindividuated within the entangled pair) have exactly the features re-quiredfor fusion. Onemightbe hesitant to usequantumentanglementsas an argumentby themselves because of the notorious difficulties n-volved in providing a realist interpretation or the theory. But whatseems to me to be a powerful argumentin favor of the existence ofthese emergentfeatures is that these quantumentanglementsare thesourceof macroscopicphenomenathat aredirectlyobservable.Inpar-ticular, the phase transitions that give rise to superconductivityandsuperfluidityn helium are a direct result of nonseparablestates.23It is a questionof considerable nterestwhether,and to whatextent,fusion occursin other areas. It would be a mistake to speculateon suchmatters,because the existenceof suchinteractions s a contingentmat-ter, to be settledby scientific nvestigation.There is indeed,within thatpart of metaphysicsthat can be (partially)naturalized,an importantbut neglected principle: certain metaphysical questions cannot be an-swered (yet) because we do not know enough. On the basis of this prin-ciple, those readers who want an answer as to whether,for example,mentalphenomenaare emergent n the above sense will, I am afraid,have to be patient.There is one other way in which fusion can occur, and it is neithera matter of speculationnor somethingdirectlyamenableto empiricalinquiry.To see it, one simplyneeds to be remindedof somethingthathas been lost in the avalancheof logical reconstructionsof causationand otherconceptsin thiscentury.It is thatsingularcausal interactionsbetween propertyinstances,construedrealistically,provide 'horizon-tal' examplesof the kind of novelty that has here and elsewherebeendiscussedin 'vertical' erms.By 'construedrealistically', mean'takento be sui generis features of the world, the propertiesof which arefundamentallymisrepresentedby reductiveanalysesor (humean)su-pervenience reatmentsof causation'.24 his is not theplaceto persuade22. See, e.g., Beltramettiand Cassinelli1981,65-72.23. See Shimony1993,221.24. I focus on causalinteractionshereonly becauseof theirfamiliarity.Other kindsofinteractionscan, one assumes,produce genuine novelty.

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HOW PROPERTIES EMERGE 17readersof the benefits of the realist singularview,25 o I shall simplynote that the issues of 'horizontal'and 'vertical'noveltyareconnected,for the explaining away of the former, especially by supervenience,tends to gainits plausibility rom a sparseontology of spacetimepointspossessinga restrictedset of primitivephysicalproperties.If you be-lieve, in contrast, that solid state physics (for example)is more thanjust advancedelementaryparticle physics, you will begin to ask howphenomenafrom the two fields interact.You should thenbe preparedto find that emergencemay be complicated,but that it is neithermys-teriousnor uncommon.26

REFERENCESBeltrametti, E. and G. Cassinelli (1981), The Logic of QuantumMechanics. Reading, MA,Addison-Wesley.d'Espagnat, B. (1965), Conceptionsde la physiquecontemporaine.Paris: Hermann.. (1995), VeiledReality. Reading, MA., Addison-Wesley.French, S. (1989), Individuation,Supervenience,and Bell'sTheorem ,PhilosophicalStudies55: 1-22.Healey, R. (1991), Holism and Nonseparability , Journalof Philosophy 88: 393-421.Humphreys, P. (1989), The Chancesof Explanation.Princeton: Princeton University Press.. (1996), Aspects of Emergence , PhilosophicalTopics24 (1), 53-70.--. (1997), Emergence, not Supervenience , Philosophy of Science 64 Supplementaryvolume, PSA96 Part II (in press).Kim, J. (1984), Concepts of Supervenience , Philosophy and PhenomenologicalResearch45: 153-176.. (1988), Superveniencefor Multiple Domains , Philosophical Topics 16: 129-150..(1992), 'Downward Causation' in Emergentismand Nonreductive Physicalism ,in A. Beckermann,H. Flohr, and Jaegwon Kim (eds.), Emergenceor Reduction:Essayson the Prospects of Nonreductive Physicalism. New York: Walter de Gruyter, pp.119-138.- . (1993), The Nonreductivists's Troubles with Mental Causation , in J. Heil and A.Mele (eds.) Mental Causation. Oxford: Oxford University Press, pp. 189-210.Lewis, D. (1986), 'Causation' and 'Postscripts to Causation' , in D. Lewis, PhilosophicalPapers, VolumeII. Oxford: Oxford University Press, pp. 159-213.Schrodinger, E. (1935), Discussion of Probability Relations between Separated Systems ,Proc. of the CambridgePhil. Soc. XXXI: 555-563.Shimony, A. (1987), The Methodology of Synthesis: Parts and Wholes in Low-EnergyPhysics , in R. Kargon and P. Achinstein (eds.). Kelvin's BaltimoreLectures and Mod-ern TheoreticalPhysics. Cambridge, MA.: MIT Press, pp. 399-423.. (1993), Some Proposals Concerning Parts and Wholes , in A. Shimony, Searchfor a Naturalistic WorldView, VolumeII Cambridge:Cambridge University Press,pp.218-227.Teller, P. (1986), Relational Holism and Quantum Mechanics , British Journalfor thePhilosophyof Science 37: 71-81.Yablo, S. (1992), Mental Causation , The PhilosophicalReview 101: 245-280.

25. For a partial account, see Humphreys 1989, Section 25.26. Since this paper was first drafted in 1991 I have realized that the term 'fusion' hasa standard use in the mereological literature that is almost opposite to its use here. Ibelieve that my use is better justified etymologically, but mereology was there first. Thereader is hereby advised never to confuse the two uses.

13b. humphreys (1997) - how properties emerge

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