EmergenceAuthor(s): Robert Michael FrancescottiReviewed work(s):Source: Erkenntnis (1975-), Vol. 67, No. 1 (Jul., 2007), pp. 47-63Published by: SpringerStable URL: http://www.jstor.org/stable/27667909 .Accessed: 06/02/2012 12:19

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Erkenntnis (2007) 67:47-63

DOI 10.1007/s 10670-007-9047-0

ORIGINAL ARTICLE

Emergence

Robert Michael Francescotti

Received: 17 January 2006 / Accepted: 27 March 2007 / Published online: 3 May 2007

? Springer Science+Business Media B.V. 2007

Abstract Here I offer a precise analysis of what it takes for a property to count as

emergent. The features widely considered crucial to emergence include novelty,

unpredictability, supervenience, relationality\ and downward causal influence.

By acknowledging each of these distinctive features, the definition provided below captures an important sense in which the whole can be more than the sum of

its parts.

Keywords Downward causation Emergent properties Novelty

Parts Predictability Relationality Supervenience Wholes

Fans of emergent properties believe that sometimes the whole is more than the sum

of its parts. Since talk of emergent properties continues to remain popular in the

philosophical literature (especially in the philosophy of mind), it would be nice to

know exactly what this slogan means. Then we could decide whether emergence

actually does obtain, and if so how pervasive it really is.

Here I provide an analysis of the concept of emergence that captures each of its

widely recognized ingredients. Sections 1 and 2 highlight three of these

ingredients?novelty, supervenience, and unpredictability?the second two of

which notoriously seem to conflict. The following sections consider various ways to render the supervenience and unpredictability claims compatible, ending in

section 5 with the definition I favor. It is then shown, in section 6, how the definition

proposed captures another commonly recognized ingredient, downward causal

influence, and how this feature, too, is rendered compatible with the supervenience

requirement. By capturing each of these widely recognized ingredients, the analysis

R. M. Francescotti (ISI)

Philosophy, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA

e-mail: rfrances@mail.sdsu.edu

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48 R. M. Francescotti

provided here describes an important sense in which the whole can be more than the

sum of its parts.1

1 Novelty

Novelty is considered crucial to emergence. John Stuart Mill (1843) notes that "[t]he chemical combination of two substances produces, as is well known, a third substance

with properties different from those of either of the two substances separately, or of

both of them taken together" (p. 234). Samuel Alexander (1920) claims that "[t]he

emergence of a new quality from any level of existence means that at that level there

comes into being a certain constellation or collocation of the motions belonging to

that level" (p. 45). Likewise, Lloyd Morgan (1923) tells us that "atoms combine to

form new units, the distinguishing quality of which is molecularity" while "on

another line of advance are organisms with a different kind of natural relations which

give the quality of vitality; yet higher, a new kind of natural relatedness supervenes and to its expression the word 'mentality' may ... be applied" (p. 35).

So emergent properties are novel, but in exactly what sense? One natural

suggestion is that the emergent properties of an object are novel in that they are not

exemplified by any of the object's proper parts. Bunge (1977), for instance, proposes that a property P is

' 'resultant or hereditary if P is a property of some components of

x;" and "otherwise, i.e., if no component of x possesses P, P is emergent, collective,

systemic, or gestalf '

(p. 502). It is easy to see, however, that this type of novelty?call

it novelty |?is not sufficient for emergence. Spencer-Smith (1995) has us imagine "an object x weighing 10 kilos, consisting of 10 components y each weighing roughly 1 kilo." Since "x has the property weighs 10 kilos which none of those y have,"

weighing 10 kilos is a novel] property of the whole. But Spencer-Smith notes that we

should not consider it emergent, for if we do, then we fail to honor "[t]he Gestalt

principle that the whole is not the sum of the parts," a principle that "embodies an

important part of what the concept of emergence is aiming at" (pp. 116-117). For a sense of "novel" that comes closer to capturing the idea that the whole is

more than the sum of the parts, one might turn to Mill's homeopathic/heteropathic distinction. Homeopathic laws govern cases in which "the joint effect of several causes is identical with the sum of their separate effects" (1843, p. 243). Suppose "a body is propelled in two directions by two forces, one tending to drive it to the

north and the other to the east." In that case, "it is caused to move in a given time

exactly as far in both directions as the two forces would separately have carried it."

Heteropathic laws, on the other hand, govern cases in which the joint effect

of causes is more than a simple sum of their effects taken separately, including

when the chemical combination of two substances produces a third substance

with properties different from those of either of the two substances separately.

1 While several well-known emergentist passages are quoted below, I do not provide a detailed historical

analysis. This has already been done by others, and much better than I can do here. See, for example,

Stephan (1992) and McLaughlin (1992). Also see Caston's (1997) brilliant discussion of the debate

between epiphenomenalism versus emergentism in the works of Aristotle and his contemporaries.

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Emergence 49

G. H. Lewes (1875) calls effects of the former sort resultant, while the latter warrant

the title "emergent."

To honor Mill's homeopathic/heteropathic distinction, we need to find a sense of

novelty that does not apply to mere resultants. Spencer-Smith proposes that "a

property P is novel in x if x has P, and there are no determinates P' of the same

determinable as P, such that any constituents of x have P' (1995, p. 117). Call this

brand of novelty, novelty2. Weighing 10 k is novel b but it is not novel2 since 10 k

and 1 k are both determinates of the determinable, weight. So novelty2 helps us

correctly classify the weight of our 10 k composite.2 While talk of novelty2 expresses a sense in which the whole is more than the sum

of its parts, there is a problem with including it in a definition of emergence. It seems that novelty2 is not necessary for emergence, and for the same reason

novelty! is not necessary. Many proper parts of you and me have mental properties,

including properties of the conscious variety. Consider me minus my left thumb or

you minus a toenail; these proper parts are conscious just as the whole is conscious.

Since we share conscious properties with some of our proper parts, thereby having determinates of the same determinable, consciousness is neither novel j nor novel2

for you or me as a whole. But it should not follow, at least not from this fact, that consciousness is non-emergent.3

To ensure a necessary condition, suppose we settle for novelty3. A property is

novel3 just in case not all proper parts have determinates of the same determinable. While some of our proper parts have conscious features, not all of them do; consider

the right knee or the left toenail. So with novelty3, consciousness is not prevented from being emergent. The problem now, however, is that while novelty3 is

necessary for emergence, we no longer have an interesting sense in which emergent

properties are novel. Consciousness and being alive are novel3, but so, too, are a

wide variety of run of the mill properties. Not all of the proper parts of a beer bottle, a bucket, a heap, or a boulder have determinates of the same determinable; but these features do not seem emergent.

Of the three senses of novelty considered thus far, novelty2 comes closest to

capturing the idea that the whole is something more than the sum of its parts. We saw, however, that it fails to provide a necessary condition for emergence.

2 Note that Spencer-Smith does not consider novelty2 sufficient for emergence. He introduces it as the

sort of novelty that, together with other features, yields emergence. The definitions he presents on pages 117-121 add to the novelty criterion. What he calls the radical conception of emergence adds that no

physical theory of the components of x can explain or predict x's having the emergent property. The

notion of epistemic emergence is theory-relative, adding that theory T can neither predict nor explain x's

having the emergent property. And the interactional conception of emergence he mentions requires that x's having the emergent property is explained by interactions between x's components. 3

Moreover, Crane (2001) notes that Spencer-Smith's definition (what we've called novelty3) is not

necessary for what we would ordinarily consider novelty. "[Consider a uniformly blue object O that can

be divided into two parts, both of which are blue. Here O has a color, and two of its parts have a

determinate property?blueness?of the determinable color. ... Yet a color is something objects can have

only when they reach a certain size, so surely it ought to be classified as novel" (p. 211). This example is meant to show that being novel2 is not necessary for what we would normally consider novel, since the

color of object O is not novel2 but is novel at least in the sense that it arises only at a certain level.

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50 R. M. Francescotti

To identify a more suitable sense of "novelty," perhaps we first need to consider

the other typical ingredients.4

2 Unpredictability and supervenience

CD. Broad (1925) claims that when hydrogen and oxygen combine to form water

"we have a clear instance of a case where, so far as we can tell, the properties of a

whole composed of two constituents could not have been predicted from a knowledge of the properties of these constituents taken separately, or from this combined with a

knowledge of the properties of other wholes which contain these constituents"

(p. 63). If we insist that emergent properties cannot be predicted from knowledge of

the properties of the parts, then we avoid classifying weighing 10 k as an emergent

property of x. Assuming that the weight of x is a straightforward sum of the weight of

its parts, then x's weight is easily predicted from the properties of the parts.

The importance of unpredictability to the concept of emergence is one thing that

makes the concept especially difficult to understand, for the unpredictability constraint seems to conflict with another feature typically considered essential. Alexander claims

that "[o]ut of certain physiological conditions nature has framed a new quality mind, which is therefore not itself physiological though it lives and move s and has its being in

physiological conditions" (1920, p. 8, emphasis added). And Broad notes that "the

properties of silver-chloride are completely determined by those of silver and of

chlorine; in the sense that whenever you have a whole composed of these two elements

in certain proportions and relations you have something with the characteristic

properties of silver-chloride" (1925, p. 64). Alexanderand Broad are expressing what

Kim ( 1993) calls mereological supervenience, according to which, the properties of an

object supervene on the properties of the object's parts. To say that emergent

properties supervene on the properties of an object's parts is to say that if x and y have

parts with all of the same properties, then x and y have all the same emergent

properties. Equivalently, x and y can differ with respect to emergent properties only by

differing with respect to the properties of their parts.5,6

4 One sense of novelty that was not considered here is historical novelty, an example of which might be

emergent evolution. Unlike the brands of novelty I discussed, historical novelty is diachronic in character?

i.e., the properties of the whole at one time are novel with respect to the properties of the parts at some earlier

time. This differs from synchronie novelty, where the properties of the whole at one time are novel with

respect to the properties of the parts at that same time. More will be said about synchronie versus diachronic

relations between parts and wholes at the end of Sect. 3 in connection with supervenience. 3

The properties of the parts include relational properties. Kim says mereological supervenience is "the

thesis that properties of wholes supervene on the properties and relations characterizing their parts"

(p. 166). Note also that the thesis is plausible only if the supervenience base includes relations the parts bear to items external to the whole. For example, if the externalist regarding mental content is correct, then the content of a mental process supervenes on relations the process bears to the external items that it

represents. Or suppose that the function of certain biological features is to be understood in terms of their

ancestry, the work these features evolved to perform. In either case, the base on which the emergent

property supervenes needs to include relations the parts bear to what lies outside of the organism. 6

While most accounts consider supervenience an important part of emergence, there are exceptions. For

example, Humphreys (1997a, b) describes emergence in terms of 'afusi?n process, in which the subvenient

lower-level property-instances go out of existence when they become fused as they give rise to higher-level

emergent property-instances. So the former no longer exist to serve as a supervenience base for the latter.

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Emergence 51

The tension between the supervenience and unpredictability constraints should be

obvious. Suppose property F of the whole supervenes on (i.e., is guaranteed by)

properties G, H and I of the parts. In that case, it should be possible, at least in

principle, for us to learn enough about G, H and I to predict that if the parts have

those properties, then the whole has F. And given supervenience, we should be able

at least in principle to learn that this conditional is true prior to actually seeing parts

coming together with properties G, H and I. So it seems that supervenience allows

precisely what the unpredictability claim denies.

3 An appeal to superdupervenience

To say that one set of properties supervenes on another is to say that the two sets of

properties covary in the following way: there is no difference in the former set

without some difference in the latter. But Kim admits that saying only this much does not tell us what grounds the covariance. We learn that mental properties, for

example, depend on physical properties without learning why this dependence relation obtains. As a result, the mind-body supervenience thesis is compatible with

a type-identity theory (since every set of properties trivially supervenes on itself) as well as certain varieties of substance dualism (versions holding that changes in the immaterial soul require changes in the associated physical body). So materialists/

physicalists should not be content with the supervenience claim. They should also endorse what Horgan (1993) calls "superdupervenience," "viz., ontological

supervenience that is robustly explainable in a materialistically acceptable way" (p. 566).

If a property were not explainable in a materialistically acceptable way, then it would not be predictable in a materialistically acceptable way either. So the notion of superdupervenience shows how supervenience might obtain without predictabil ity. The proposal would be that emergent properties are those that supervene without

superdupervening. That is,

(1) F is an emergent property of composite x =df F nomologically supervenes on the properties of x's proper parts, but this fact cannot be explained in a

materialistically acceptable way.

What would count as a materialistically acceptable explanation? The functional model of explanatory reduction provides one example. Levine (1993) notes that on one model at least, "explanatory reduction is, in a way, a two-stage process." The

first stage involves "working the concept of the property to be reduced 'into shape' for reduction by identifying the causal role for which we are seeking the underlying

mechanisms," and the second stage "involves the empirical work of discovering

just what those underlying mechanisms are" (p. 132). Kim's (1999) model of

explanatory reduction adds a third stage. Kim notes that the explanation is not

complete until the third step, which is to find a theory telling us how it is that the realizers of a functional property play the causal role definitive of that property.

If one considers the functional model as definitive of explanatory reduction, one

might conclude from (1) that emergent properties are best characterized as those

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52 R. M. Francescotti

that elude the functional model. Thus, Kim (1998) proposes that "a property M is

emergent relative to a given domain D of properties just in case M is not

functionalizable in terms of properties in D" (p. 19). Suppose, for example, that

Levi ne is correct about the explanatory gap between the physical and the

phenomenal. Then the third step of Kim's functional model is not fulfilled where

phenomenal (qualitative) states are concerned, in which case they qualify as

emergent on his definition.

As noted above, if a property were not explainable in a materialistically

acceptable way, then it would not be predictable in a materialistically acceptable

way either. So it seems that definition (1) makes supervenience perfectly compatible with unpredictability. There is, however, one major problem with the definition. The

notion of explanation is an epistemic notion. To explain why a certain phenomenon

obtains is to enable one to understand why it obtains; a phenomenon has not been

successfully explained until it has been made comprehensible. But there are worries

about treating emergence as an epistemic affair. Broad characterizes emergent

properties as those that could not be predicted even in principle: they are properties of a whole that "could not, even in theory, be deduced from the most complete

knowledge of the behavior of its components, taken separately or in other

combinations, and of their proportions and arrangements in this whole" (1925,

p. 59). Since talk of predictability "in theory" is meant to abstract away from

epistemic limitations, it seems that ontological emergence is the notion of interest

here?and perhaps rightly so, for as Spencer-Smith claims, "[e]mergent nature is

not something which should change over time" (1995, p. 121). It would seem, then, that against viewing emergence as supervenience without superdupervenience, one

can complain with Reuger (2000) that "the doctrine of emergence, if explicated in

terms of a failure of explainability, seems to turn from a metaphysical position into

an essentially epistemic doctrine" (p. 471). Since the notion of emergence is a piece of technical jargon and a sufficiently

unclear piece at that, we should hesitate to say that emergence must never be

considered an epistemic affair. In certain contexts, it might be legitimate and even

useful to have an epistemically loaded account.7 Still, it would be nice if we could

find a consistent account of genuine ontological emergence, since being more

than the sum of the parts (a very common way of thinking about emergence) does

seem to be an ontological matter. Stephan notes that "[i]f we leave open whether it

is possible to deduce or predict the properties considered, and ask whether

the system properties are determined by the properties of the parts we take the

ontological stance" (1992, p. 30). Let's follow Stephan's advice and replace the

unpredictability constraint with the following underdetermination thesis: the

emergent properties of the whole are underdetermined by the properties of its

proper parts.

The supervenience thesis Kim has in mind, and the one often considered crucial

to emergence, is designed to express a synchronie relation; if x has emergent

7 For epistemically loaded accounts of emergence other than Kim's, see Cunningham (2001) and

Newman (2001). One might even argue for the value of a pragmatic conception of emergence, e.g.,

Pihlstrom and Nino-El-Hani (2002).

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Emergence 53

property F at time t, the properties of the parts on which F supervenes are also

exemplified at t.8 The underdetermination claim should also be viewed as

expressing a synchronie relation. The question is not whether the properties of

the parts at one time underdetermine the properties of the whole at a later time, for

causal indeterminacy should not automatically guarantee the presence of emergent

properties. The crucial question is whether the properties of the parts at one time

underdetermine the properties of the whole at that same time.

Given that we are concerned with synchronie underdetermination, the conflict

with the supervenience relation is especially threatening. We are being asked to

imagine that the emergent properties of the whole at a certain time are determined

by, and yet not determined by, the properties of the parts at the very same time. One

might conclude from this that the notion of emergence is simply incoherent. But this

is too hasty. Perhaps we should conclude instead that in one sense of "determined,"

emergent properties are determined by the properties of the parts, and in another

sense, emergent properties are not determined by the properties of the parts.

The task, then, would be to figure out what these two different senses are.

4 Nomological versus logical necessity

A determination relation might obtain as a matter of logical necessity or it might obtain only as a matter of nomological necessity. Suppose that mental properties supervene on physical properties as a matter of nomological necessity. Then the

facts about which physical properties are exemplified together with the laws of nature entail all the facts about which, if any, mental properties are exemplified. Are there possible worlds with different laws of nature, perhaps even laws that allow

disembodied minds? If so, then while mental properties nomologically supervene on

physical properties, they do not logically supervene.

Applying the distinction between logical and nomological supervenience to

emergent properties, we might accept van Cleeve's (1990) proposal that "[i]f P is a

property of w, then P is emergent iff P supervenes with nomological necessity, but not with logical necessity, on the properties of the parts of w" (p. 222). That is,

(2) F is an emergent property of composite x =df F nomologically supervenes, but does not logically supervene, on the properties of x's proper parts.9

Definition (2) entails that given the laws of nature, any two composites with

indistinguishable parts will be alike in terms of emergent properties. What (2)

8 One good reason for treating supervenience as synchronie is to allow the underdetermination of effects

by their causes. If causes underdetermine their effects, then the properties exemplified at one time do not

guarantee which properties are exemplified at some later time, in which case, the latter set of properties does not supervene on the former. Yet, even if causes underdetermine their effects, we still might wonder

what it is about an individual at a particular time that guarantees the individual has certain emergent

properties at that time. (Although, O'Connor 2000, argues that the type of supervenience relevant to

emergence should be considered a diachronic relation.) 9

Like (1), definition (2) mentions proper parts. It is trivially true that any property of any object is

exemplified by the object's improper part, and also that every property logically supervenes on itself. So

without reference to proper parts, we risk classifying all properties as non-emergent.

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54 R. M. Francescotti

denies is that the laws of logic alone guarantee this. So the definition satisfies two

common intuitions about emergent properties: that they supervene even though they are underdetermined.

However, O'Connor (1994) claims that van Cleeve's definition "counts a wide

range of properties as ?mergents that quite clearly do not belong to that category"

(p. 96). It seems, for example, that "the potentiality of a knife to slice a loaf of bread

is a macro-property that supervenes on the properties of its molecular constituents

with nomological necessity only" (p. 96). The bread-cutting potential of a knife

does not seem to be the sort of property emergentists have in mind when they claim

that the whole is more than the sum of its parts. So van Cleeve's analysis appears to

give the wrong result in this case. O'Connor might also refer to our 10 k object as a

counter-example, since the weight of this object is determined by the weight of its

parts only together with the laws of nature.

Can van Cleeve be defended against this type of objection? Whether we can

logically derive the fact that the knife has bread-cutting ability from facts about the

knife's parts depends on which properties of the parts we are allowed to consider.

Suppose that knife x contains part y. Then y has the property, is a part of knife x

which possesses bread-cutting ability. So the fact that the knife has bread-cutting

ability is logically entailed by facts about the parts after all, in which case, the

knife's bread-cutting ability is not emergent according to (2). Likewise, the weight of our 10 k object is logically entailed by the following property of its parts: is part

of an object weighing 10 k. So weighing 10 k is not classified as emergent.

Unfortunately, this defense of van Cleeve's analysis reveals a truly fatal flaw

with (2). For any property F of any composite x, and any part y of x, there is a fact

about y that logically entails that x has F, namely, the fact that y is such that x has F.

So, according to (2), there are no emergent properties!

If we were to amend van Cleeve's analysis, we would need to identify some

special type of property had by the parts, and then say that emergent properties

nomologically supervene, but fail to logically supervene, on properties of that

special type. But, then, why bother with logical supervenience at all? Perhaps we

can isolate some special type of property of the parts on which ?mergents

nomologically supervene, and without which they fail to nomologically supervene. In that way, we can still honor both the supervenience and the underdetermination

constraints.10

10 Or we might say, instead, that with respect to one class of properties, ?mergents logically supervene,

but relative to another they do not. But this does not seem right, for whether a property is emergent should

not be solely a matter of logic. Even if a property were emergent in all of its actual exemplifications (for

example, even if life or consciousness always turned out to be emergent), it is arguable that this fact

should have something to do with the laws of nature that actually obtain. Suppose that x and y have

qualitatively identical proper parts that are related to one another in all the same ways. Also suppose that

x and y both have property F, and that F is emergent for x. It should not be logically inevitable that F is

emergent for y. The laws of nature that obtain at a world affect how the parts and their interrelations give rise to the properties of the whole at that world. So a difference in inter-level laws (trans-ordinal laws, as

Broad calls them, 1925, p. 77 ff.) might yield a difference not only in the properties of the whole but also

a difference in how the properties of the whole depend on the properties of the parts and their

interrelations. Thus, a change in inter-level laws from one logically possible world to another might make

a difference in which properties are emergent at that world.

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Emergence 55

5 An appeal to relationality

Relationality seems crucial to emergence. As Broad notes, "the emergent theory

asserts that there are certain wholes, composed (say) of constituents A, B, and C in a

relation R to each other; that all wholes composed of constituents of the same kind

as A, B, and C in relations of the same kind as R have certain characteristic

properties" (1925, p. 61). Likewise, Teller (1992) proposes that "[a]n emergent

property of a whole is one which transcends, in the sense of not reducing to, that is

not being explicitly definable in terms of, the non-relational properties of the parts"

(p. 144).n Causal relations might be considered especially important. What Searle (1992)

calls causally emergent system features are features of a system that "cannot be

figured out just from the composition of the elements and environmental relations;

they have to be explained in terms of the causal interactions among the elements"

(p. 111).12 But let us leave open whether the requisite relations between the parts are

causal relations and simply propose that

(3) F is an emergent property of composite x =df F nomologically supervenes on the properties of x's proper parts, but not on the intrinsic properties of those

parts,

where the intrinsic properties of an object are those the object has not in virtue of its

relation to anything external to itself. According to (3), there is a sense in which

emergent properties supervene and a sense in which they do not. They supervene if the supervenience base includes relational properties of the parts; otherwise, they do

not supervene.

Definition (3) improves on (2) by allowing a wide range of ontologically

emergent properties. Unfortunately, it allows too wide a range. Recall object x that

weighs 10 k. There are nomologically possible worlds at which those 10 parts each

weigh 1 k but x does not weigh 10 k because not all of those parts are parts of x or

perhaps because x has more than those ten parts. So the fact that each of the ten

components weighs 1 k does not entail that x weighs 10 k without the assumption that those ten components are parts of x along with the additional assumption that

they are the only parts of x. Since x's weight supervenes only with the help of non

intrinsic properties of the parts, (3) misclassifies weighing 10 k as an emergent

property of x.

Although (3) fails, by highlighting relationality it does bring us closer to an

adequate definition. A property's being emergent does have a lot to do with the

relational properties of the object's parts. It's just that some restrictions must be

placed on the relations that secure supervenience. We should expect that there is

some special type of relationality that is essential to emergence. What special type of relationality might that be? Morgan provides an answer:

11 Also see Teller (1986) for more on the importance of relationality to emergence.

12 Searle labels this concept of emergence, emergent], which is "to be distinguished from a much more

adventurous conception, call it 'emergent2.' A feature F is emergent2 iff F is emergent 1 and F has causal

powers that cannot be explained by the causal interactions of a, b, c ..." (p. 112).

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56 R. M. Francescotti

when some new kind of relatedness is supervenient (say at the level of life), the way in which the physical events which are involved run their course is

different in virtue of its presence -

different from what it would have been if

life had been absent. (1923, p. 16, emphasis added)

If being alive is emergent, then it supervenes on the properties of an object's proper

parts, and Morgan says, these properties include those the parts would lack if they were not parts of a living object. If this is correct, then the properties that give rise to

life are dependent on, had in virtue of, the presence of life itself. Thus,

(4) F is an emergent property of composite x =df (i) F nomologically supervenes on the properties of x's proper parts; and (ii) for any set Z of

properties of x's proper parts, if F nomologically supervenes on Z, then there

is at least one member of Z the parts would lack if they were not parts of a

whole with F.

The properties of the parts that secure supervenience will certainly include relations

that the parts bear to one another. According to (4), they also include relations the

parts bear to the whole, especially the relational feature noted by Morgan?that the

parts would differ if they were not parts of an object with the emergent property. Note that (4) says "for any set Z of properties of x's proper parts" rather than

"for some set Z of properties ..." With only the existential quantifier, every property

of a composite would count as emergent. Take any property F of any composite x,

and take any set of properties of the proper parts on which F supervenes. Now add

the property, is part of a whole that has F. F also supervenes on this slightly larger set, a set that includes a property the parts would lack if they were not parts of a

whole with F. So with only the existential quantifier, F is classified as emergent. The

universal quantifier is required to capture the idea that if F is emergent, its

supervenience always involves parts that are as they are because they are parts of an

object with F, that no arrangement of parts could guarantee the presence of F

without their being parts of a whole that is F.

What about our 10 k composite? There are certain properties that must be

included in the supervenience base if x's weight is to supervene on the properties of

its parts. For example, the weight of each of the individual parts must be included,

along with the relational property of being parts of the same whole. But none of the

requisite features depends on the parts being parts of a whole weighing 10 k. Each

part might still weigh 1 k even if it were part of a smaller or larger whole, and the

parts might still be parts of the same whole even if they were not parts of a whole

weighing 10 k. So in this case, there is a class of properties of the parts on which the

weight of x supervenes, and which does not include a property the parts have in

virtue of being parts of a whole with that weight. In this case, then, (4) avoids

classifying the composite's weight as emergent.

However, there is a complication. Suppose that F supervenes on a set of

properties, Z. Then Z guarantees the presence of F; that is, Z -> F. So if an object were to lose F, the parts would have to undergo some change with respect to the

properties in set Z; that is, ~F -> ~Z. It is inevitable, then, that there is at least one

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property in Z the parts would lack without the presence of F. So it follows from (4) that whenever a property supervenes on the properties of the parts, it is emergent!

To avoid this unwelcome result, we should rephrase clause (ii).

(4*) F is an emergent property of composite x =df (i) F nomologically supervenes on the properties of x's proper parts; and (ii) for any set Z of

properties of x's proper parts, if F nomologically supervenes on Z, then Z

includes, as a proper subset, at least one property the parts would lack if they were not parts of a whole with F.

With the "proper subset" qualification, we avoid the worry that (ii) is trivially satisfied by every set of properties on which F supervenes. Many sets of properties

will satisfy (ii). For any set Z* on which F supervenes, add the property, is part of a

whole with F, and call this larger set, Z**. Since Z** contains Z*, F supervenes on

Z** as well. Also, since F supervenes on Z* and Z* is a proper subset of Z**, it

follows that there is a proper subset of Z** whose presence guarantees that the

whole is F. So Z** is one subvening set that satisfies condition (ii). However, it need not be this way with every subvening set. Suppose that F is the property, weighs 10 k, and suppose that Z* is a minimal supervenience base.13 That is, suppose Z*

contains only those properties that are required for the whole to weigh 10 k; for any

property of Z*, if that property were not exemplified, the whole would have a

different weight. In this case, whatever proper subset of Z* we choose, that subset

could obtain in the absence of F. As noted above, it is possible for each of the parts to weigh 1 k without the whole weighing 10 k, for they might have been parts of

different wholes. Even assuming they are parts of the same whole, F could still have

been absent, for there could have been more than ten parts. So in this case, the word

"any" in condition (ii) together with the proper subset qualification prevents us

from classifying x's weight as emergent.

Condition (ii) states that emergent properties supervene on the properties of the

proper parts, but only if we include properties the parts have in virtue of being parts

of a whole with F. We thereby honor the idea that the subvening events proceed as

they do in virtue of being parts of a whole with the emergent property. As Morgan said, the way the subvening events run their course is different in virtue of its

presence. Condition (ii) also explains Broad's claim that the emergent property "could not have been predicted from a knowledge of the properties of these

constituents taken separately, or from this combined with a knowledge of the

properties of other wholes which contain these constituents" (1925, p. 63, emphases added). The emergent property supervenes on the properties of the parts, and it is

therefore possible, at least in principle, to predict its presence on the basis of those

properties?but only if the properties of the parts include properties they have in

virtue of being parts of a whole with the emergent property. Otherwise, the

emergent property does not supervene, in which case it is underdetermined and

therefore unpredictable.

Teller (1986), Humphreys (1997a), and Silberstein (1998), among others, have

argued that quantum mechanics provides strong evidence for the existence of

13 Kim (1984, p. 164) introduces the idea of maximal and minimal bases.

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58 R. M. Francescotti

emergent properties. If they are correct, then emergence is indeed ubiquitous.

Definition (4*), however, shows that examples of emergence are far easier to come

by. If (4*) is correct, then the British emergentists were right to classify the property of being H20 and the property of being silver-chloride as emergent. While each of

these properties supervenes on features of the constituent atoms, the features of the

atoms on which it supervenes include features that the atoms have only by virtue of

being parts of that compound. The atomic interrelations that give rise to the

compound would not obtain if the atoms were parts of a different molecular type. (4*) also classifies life as emergent. An organism is alive in virtue of certain features

of its parts, and at least some of those features are dependent on being parts of a

living organism, dependent in that the parts would lack those properties if they were

not parts of a living organism. The capacity for metabolic activity, in particular, is

emergent. For as Jones (1972) notes, this capacity is a "property which the human

body, considered as a complex whole, possesses by virtue of the particular

combination and arrangement of its constituents, but which is not possessed by the

constituents in isolation or in other non-living combinations" (p. 425).

Definition (4*) allows us to agree with Sperry (1976) that consciousness is

emergent, for while mental properties supervene on neural properties, the

"conscious subjective properties ... have causal potency in regulating the course

of brain events; that is, the mental forces or properties exert a regulative control

influence in brain physiology" (p. 165). So the neural processes on which

consciousness supervenes are themselves dependent on the role they play within the

conscious system. The neural events instantiate properties that enable them to give

rise to consciousness, but at the same time at least some of those properties are

features the neural events would not instantiate had they not occurred within a

conscious system. Various properties of the social sciences are also classified by

(4*) as emergent. The property of social cohesion, for example, depends on the

behavior of the individual members of the group. At the same time, the behavior of

the individual members is dependent on the interrelations that give rise to social

cohesion.14 It seems, then, that if (4*) is an accurate definition, emergence is hardly an isolated phenomenon; there would appear to be countless instances across a wide

range of scientific disciplines.15 What (4*) does preclude are properties of purely mechanical systems, where

"the behaviour of the whole could, in theory at least, be deduced from a sufficient

knowledge of how the components behave in isolation or in other wholes of a

simpler kind" (Broad, 1925, p. 59). Consider the behavior of a traditional clock, for

example. "We know perfectly well," Broad says, "that the behavior of a clock can

be deduced from the particular arrangement of springs, wheels, pendulum, etc., in it,

and from general laws of mechanics and physics which apply just as much to

material systems which are not clocks" (1925, p. 60). What makes the behavior of

the clock non-emergent, according to (4*), is that the properties of the parts on

14 See Sawyer's (2004) detailed discussion of how social properties emerge.

13 Dynamic systems theory is also thought to illustrate emergence. See, of example, Cummingham

(2001) and Newman (2001), the latter of whom further argues that the brain is a chaotic, nonlinear

dynamic system. Also see Silberstein and McGeever's (1999) discussion of whether nonlinear dynamic

systems are evidence of emergence.

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Emergence 59

which the behavior of the whole (e.g., telling the correct time and striking on the

hour) supervenes are properties the parts could still have in isolation from the

whole. It is precisely for this reason that the behavior of the clock could, in theory at

least, be deduced from a sufficient knowledge of how the components behave in

isolation or in other wholes of a simpler kind. The same is true of any other purely mechanical system. Suppose the behavior of a system can be deduced from

sufficient knowledge of how the components behave in isolation or in other wholes

of a simpler kind (thereby qualifying the system as purely mechanical). Then the

properties of the parts on which the behavior of the whole supervenes are properties the parts could still have independently of the system, which are precisely the

properties (4*) classifies as non-emergent.

It was shown how (4*) makes the supervenience thesis compatible with the

underdetermination constraint. It is now time to revisit the novelty issue. Of the

three varieties of novelty discussed in section 1, novelty2 comes closest to capturing

the idea that the whole is something more than the sum of its parts. Recall, however,

that novelty2 is not necessary for emergence since the emergent properties of an

object might be exemplified by parts of the object. Thanks to definition (4*), we are

now in a position to identify a more suitable brand of novelty.

6 Novel and downward causal influence

Alexander insists that an emergent property is not epiphenomenal, for to suppose it

lacks causal powers is to suppose "something to exist in nature which has nothing to do, no purpose to serve, a species of noblesse which depends on the work of its

inferiors, but is kept for show and might as well, and undoubtedly would in time be abolished" (1920, p. 8). Sperry (1976) takes "the stand that wholes and their

properties are real phenomena, and that these and their causal potency are just as

important as the properties of the parts ...," since "the spatial and the temporal

relationships of the constituent parts of a system have in themselves important causally efficacy over and above the properties of the parts per se" (p. 167). And Silberstein (1998) characterizes emergent properties as "qualitatively new proper ties of systems or wholes that possess causal capacities that are not reducible to any

of the causal capacities of the parts" (p. 468). It seems, then, that we should add to our list of criteria that emergent properties

have causal powers and novel causal powers as well, novel in the sense that they are

distinct from the causal powers of the object's parts. Or, focusing on Sperry's talk of

"causal efficacy over and above the properties of the parts per se," perhaps we

should say that emergent properties have causal powers that are novel in the sense

that they are distinct from the causal powers of the object's parts taken in isolation

from the whole.

The novel causal powers constraint may already be entailed by definition (4*). Clause (ii) tells us that at least some of the subvening properties would not be

exemplified without the relevant parts being parts of a whole with the emergent

property. This entails that the emergent property has a novel influence, novel in

being distinct from the influence of the parts taken in isolation from the whole.

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60 R. M. Francescotti

Whether this novel influence is also thought to be a causal influence depends on

one's theory of causation. For example, if a counterfactual account of causation

were correct, the influence of emergent properties would qualify as causal (since we

are assuming that if the emergent properties were not present, the parts would be

different). In any case, suffice it to say here that if one does not think (4*) entails

novel causal powers, one can modify clause (ii) to make the requirement clear.

(4**) F is an emergent property of composite x =df (i) F nomologically supervenes on the properties of x's proper parts; and (ii) for any set Z of

properties of x's proper parts, if F nomologically supervenes on Z, then Z

includes as a proper subset at least some properties that are causally dependent

on being parts of a whole with F.

By endorsing supervenience, we require that emergent properties are entirely a

function of the properties of the parts and their interrelations. But if they are, then

how could they have a novel causal influence? The way underdetermination was

reconciled with supervenience in section 5 shows how to answer this question.

Remember: an emergent property F supervenes on the properties of the proper parts,

but only if we include properties the parts have in virtue of being parts of a whole

with F. This also applies to F's causal powers. F's causal powers supervene only if

we include properties the parts have in virtue of being parts of a whole with F. So

these causal powers supervene, and yet they are novel?novel in the sense that they are distinct from the causal powers of the object's parts taken in isolation from the

whole.

So we get novel causal powers, but do we also get novel causal powers with a

downward influence?an influence on the properties of the parts? Sperry (1991) notes that supervenience is compatible with downward causal influence, provided

that "the higher-level phenomena in exerting downward control do not disrupt or

intervene in the causal relations of the lower-level component activity." They

supervene "in a way that leaves the micro interactions, per se, unaltered" (p. 230).

But how can downward causation, causation directed toward the parts, not involve

an alteration or disruption of the parts? To say that F has a causal influence on the

properties of the parts implies that the properties of the parts somehow differ in

virtue of F's presence. This certainly sounds like some sort of intervention.16

To avoid the conflict, an emergentist might settle for downward causation of the

diachronic variety. Recall that the supervenience relation is supposed to be

synchronie; the properties of the parts at a time guarantee the presence of the

emergent property at the same time. This synchronie upward determination is

perfectly compatible with the emergent property causally influencing the properties that the parts will have at some later time. However, the notion of an emergent

property seems to imply something stronger than diachronic downward causation.

Emergentists seem to be claiming that while life, mentality, and molecular

composition are secured by the properties of the parts, these emergent properties

16 The type of downward causation at issue here is what Kim (1998, 1999) calls reflexive downward

causation (as opposed to the causal influence of a whole on the proper parts of a distinct whole, which is

no threat to mereological supervenience). Also note that this conflict is a purely logical conflict. For a

discussion of empirical objections to emergence, see McLaughlin (1992).

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Emergence 61

simultaneously orchestrate the behavior of the parts. The heart is not functioning as

it does because it was part of a living organism; it is functioning as it does because it

is currently part of a living organism. The property of being alive, exemplified by the whole organism, influences the current functioning of the individual organs. At

least, that is what the notion of emergence seems to imply. So the question remains:

how can we make sense of influencing in a novel way without altering or

disrupting?

Shoemaker (2002) says

to say that the causation is 'downward' is just to say that the causal powers

activated in it are ones that are activated only when their possessors are in such

a combination, and are such that the effects of their activation turn on

precisely what sort of emergence engendering combination they are involved

in. (p. 58)

Shoemaker says this to support the possibility of diachronic downward causation.

Yet, while he rejects the synchronie variety, what he says here seems to support that

as well. The idea that the effects of downward causation "turn on precisely" the

emergent engendering combination involved sounds a lot like Broad's idea that the

way in which the parts run their course is different in virtue of the presence of the

emergent property. This point is captured by clause (ii), which tells us that the

emergent property F that enables the whole to direct the behavior of the parts is a

property in virtue of which the parts are able to guarantee the presence of F. Now, downward causation is a threat to supervenience only assuming that the subvening

properties of the parts are independent of emergent property F, independent in that

each might be present on its own in the absence of F. Yet, (ii) says that this is not the

case; the subvening properties already include properties of the parts that are a

function of the whole's having F. This is what makes downward causation

compatible with supervenience.

7 Conclusion

Definition (4**) captures several ideas considered crucial to emergence. An

emergent property F supervenes on the properties of the parts. But this is only if the

supervenience base includes properties the parts have in virtue of being parts of a

whole with F. This explains the sense in which F is unpredictable. The behavior of

the parts crucial to the whole's having F is itself dependent on F. So if we consider

the behavior of the parts in isolation from the whole, if we consider them taken

separately or in other combinations, then we will miss certain facts that are crucial

for reliably predicting the presence of F.

Emergence, then, is a function of relationality. Emergent property F supervenes

only given relations the parts bear to one another. Also important are relations the

parts bear to the whole, since F supervenes only with the help of properties the parts would lack were they not parts of a whole with F. This latter fact is what makes it

possible for F to supervene and at the same time exert a novel and even downward

causal influence. The influence of F supervenes on, and therefore is solely a function

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of, the properties of the parts. Yet the influence is novel in that it goes beyond (is not

solely a function of) the properties of the parts when taken in isolation from the

whole. And because F supervenes only with the help of properties the parts would lack were they not parts of a whole with F, the base on which F supervenes is

dependent on the presence of F itself. In this way, F influences the properties of the

parts without violating the supervenience relation.

Whether (4**) captures everything everyone wants from the notion of

emergence, it does recognize each of its most popular ingredients. It thereby

captures an important sense in which the whole might be more than the sum of its

parts.

Acknowledgements Thanks to Mark Wheeler and the referees at Erkenntnis for valuable comments on

earlier drafts of this paper.

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