Emergence is a notorious philosophical term of art. A variety of theorists have appropriated it for their purposes ever since George Henry Lewes gave it a philosophical sense in his 1875Problems of Life and Mind. We might roughly characterize the shared meaning thus: emergent entities (properties or substances) ‘arise’ out of more fundamental entities and yet are ‘novel’ or ‘irreducible’ with respect to them. (For example, it is sometimes said that consciousness is an emergent property of the brain.) Each of the quoted terms is slippery in its own right, and their specifications yield the varied notions of emergence that we discuss below. There has been renewed interest in emergence within discussions of the behavior of complex systems and debates over the reconcilability of mental causation, intentionality, or consciousness with physicalism.2. Epistemological Emergence
3. Ontological Emergence
3.1 The Standard Ontology of Emergence: Supervenience Emergentism
3.2 Alternative Conceptions of Ontological Emergence
3.3 Objections to Emergence
4. Possible Applications
5. Emergent Substance
Bibliography
Further Reading
References
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[size=30]1. A Brief History
British emergentists of the late-nineteenth and early-twentieth centuries may not have been the first to embrace emergentist ideas (Caston 1997 provides evidence that Galen was an emergentist), but they were certainly the first to work out a comprehensive emergentist picture. Much of the defense of emergentism in this era was centered on chemistry and biology. The question was whether or not the constitutive principles and features of these sciences were reducible to those of the corresponding ‘lower level’ sciences of physics and chemistry, respectively. Reduction-minded ‘mechanists’, who supposed that the processes of life were governed wholly by physical-chemical principles, contended with the extreme anti-reductionist ‘vitalists,’ who posited an entelechy, a primitive substance or directing principle embodied in the organism which guided such characteristic vital processes as embryonic development and the regeneration of lost parts.
[1] Emergentists sought to develop a middle way, eschewing vital substances but retaining — in
some sense — irreducibly vital qualities or processes.
1.1 J.S. Mill
Here is the early exponent of emergentism, J.S. Mill:
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- اقتباس :
- All organised bodies are composed of parts, similar to those composing inorganic nature, and which have even themselves existed in an inorganic state; but the phenomena of life, which result from the juxtaposition of those parts in a certain manner, bear no analogy to any of the effects which would be produced by the action of the component substances considered as mere physical agents. To whatever degree we might imagine our knowledge of the properties of the several ingredients of a living body to be extended and perfected, it is certain that no mere summing up of the separate actions of those elements will ever amount to the action of the living body itself. (A System of Logic, Bk.III, Ch.6, §1)
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In analyzing such phenomena, Mill introduces the notion of a
heteropathic effect and the attendant notion of a heteropathic law, in contrast to
homopathic effects and laws. He does this by way of contrasting two modes of the conjoint action of causes, the ‘mechanical’ and ‘chemical’ modes. Mill says that the essence of the mechanical mode is that the total effect of several causes acting in concert is identical to what would have been the sum of effects of each of the causes acting alone. The laws of vector addition of forces, such as the parallelogram law, are for him the paradigm example of the conjoint action of causes in the mechanical mode. The total effect of two forces
F and G acting in concert on a particle
p just is the effect of
F acting on
pfollowed by
G acting on
p. In imitation of the principle of ‘Composition of Forces’ operative in physics, Mill named the corresponding principle for causes the ‘Composition of Causes.’ In Mill's terminology, effects of multiple causes produced in the mechanical mode — i.e. in accordance with the Composition of Causes — are known as ‘homopathic effects.’ Laws which subsume such causal relations between causes and their homopathic effects are known as ‘homopathic laws.’
By contrast, the chemical mode of the conjoint action of causes is characterized by a violation of the Composition of Causes: the joint action of multiple causes acting in the chemical mode is not the sum of effects of the causes had they been acting individually. This mode of conjoint action of causes is named after the chemical reactions which typically exhibit it, e.g.:
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- اقتباس :
- NaOH + HCl → NaCl + H2O
(Sodium hydroxide + hydrochloric acid produces sodium chloride + water)
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The product of this neutralization reaction, water and a salt, is in no sense the sum of the effects of the individual reactants, an acid and a base. These are ‘heteropathic effects,’ and the causal laws which subsume them are ‘heteropathic laws.’ Heteropathic laws and effects correspond to a class of laws and effects that the later British Emergentists dubbed ‘emergent.’ Mill clearly believed in the existence of heteropathic laws within chemistry and biology, while supposing it conceivable that psychology generally could be reduced to physiology.
Within each level, however, there are also numerous homopathic laws characterizing causal interactions which obey the Composition of Causes. One might wonder how homopathic and heteropathic laws interact. On Mill's account, higher-level heteropathic laws will supplement but not supplant lower-level laws (whether homopathic or heteropathic). Regarding the relations between lower-level and higher-level laws in the case of vegetable and animal substances, Mill writes:
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- اقتباس :
- Those bodies continue, as before, to obey mechanical and chemical laws, in so far as the operation of those laws is not counteracted by the new laws which govern them as organized beings. (1843, p. 431)
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The compatibility of higher-level and lower-level laws is due in some cases to lower-level laws containing
ceteris paribus clauses, and in others to the fact that lower-level dynamical laws will simply sum over more causes. For example, Newton's second law,
F =
ma, does not state that only
physical forces count. If any basic chemical or biological forces exist, they will be summed with whatever physical forces there are in the dynamical context, and that will be the value of
F in the equation.
[2]It is important to note that
both homopathic and heteropathic laws for Mill are
causal laws, and homopathic and heteropathic effects are effects of
causal interactions. Thus, Mill's
dynamicalaccount of emergence (heteropathic interactions) differs importantly from the synchronic, noncausal covariational account of the relationship of emergent features to the conditions that give rise to them that C. D. Broad was to espouse in
Mind and Its Place in Nature (1925). Mill's account is thus an important precursor to the atypical dynamical accounts of emergence in the literature today. (See the discussion of Humphreys' and O'Connor's accounts in Part IV below.)
1.2 C. D. Broad
British Emergentism reaches its zenith with C.D. Broad's monumental
The Mind and Its Place in Nature (1925), reworked from his Tarner lectures delivered at Cambridge in 1923. It is interesting to note that the aim of the Tarner Benefaction was to found a course of lectures on “the relation or lack of relation between the various sciences.” This is none other than the familiar contemporary question of the autonomy of the special sciences (Fodor 1974). We suggest below that Samuel Alexander's conception of emergentism is actually the closest parallel to the modern view known as nonreductive physicalism.
Broad sees his inquiry as aimed at answering a general question of which the debate between the Mechanists and Vitalists about living organisms is a particular instance: “Are the apparently different kinds of material objects irreducibly different?” (1925, p. 43) Broad is not merely interested in resolving the Mechanist-Vitalist controversy, but in answering the broader question of whether the special sciences are reducible to more general sciences (e.g. biology to chemistry), and ultimately to physics. He writes:
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- اقتباس :
- [One] wonders whether the question ought not to have been raised long before the level of life … The question: Is chemical behaviour ultimately different from dynamical behaviour? seems just as reasonable as the question: Is vital behaviour ultimately different from non-vital behaviour? And we are much more likely to answer the latter question rightly if we see it in relation to similar questions which might be raised about other apparent differences of kind in the material realm. (1925, p. 44)
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He suggests that two types of answers to the reducibility question can be given, mechanism and emergentism. Broad characterizes the purest form of the Mechanist position thus:
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- اقتباس :
- [There] is one and only one kind of material. Each particle of this obeys one elementary law of behaviour, and continues to do so no matter how complex may be the collection of particles of which it is a constituent. There is one uniform law of composition, connecting the behaviour of groups of these particles as wholes with the behaviour which each would show in isolation and with the structure of the group. All the apparently different kinds of stuff are just differently arranged groups of different numbers of the one kind of elementary particle; and all the apparently peculiar laws of behaviour are simply special cases which could be deduced in theory from the structure of the whole under consideration, the one elementary law of behaviour for isolated particles, and the one universal law of composition. On such a view the external world has the greatest amount of unity which is conceivable. There is really only one science, and the various “special sciences” are just particular cases of it. (1925, p. 76)
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As Broad notes, it is easy to see that there are weaker Mechanist positions which are still consistent with the idea and spirit of Mechanism, though for economy's sake we shall not explore such variants here.
The Emergentist position taken by Broad rejects the deep ontological unity posited by the Mechanist position. If emergence obtains, theorists would be forced to rest content with a hierarchy of various sciences ranging from the universal — physics — to the most specific (1925, p. 77). While Emergentists, too, are physical substance monists (“there is only fundamentally one kind of stuff”), they recognize “aggregates [of matter] of various orders” — a stratification of kinds of substances, with different kinds belonging to different orders, or levels. Each level is characterized by certain fundamental, irreducible properties that emerge from lower-level properties. Correspondingly, there are two types of laws: (1) ‘intra-ordinal’ laws, which relate events within an order, i.e., a law connecting an aggregate of that order instantiating a property of that order at a time with some aggregate of that order instantiating some other property at a certain time; and (2) ‘trans-ordinal’ laws, which characterize the emergence of higher-level properties from lower-level ones. Emergent properties are identified by the trans-ordinal laws that they figure in; each emergent property appears in the consequent of at least one trans-ordinal law, the antecedent of which is some lower-level property:
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- اقتباس :
- A trans-ordinal law would be one which connects the properties of aggregates of adjacent orders. A and B would be adjacent, and in ascending order, if every aggregate of order B is composed of aggregates of order A, and if it has certain properties which no aggregate of order A possesses and which cannot be deduced from the A-properties and the structure of the B-complex by any law of composition which has manifested itself at lower levels … A trans-ordinal law would be a statement of the irreducible fact that an aggregate composed of aggregates of the next lower order in such and such proportions and arrangements has such and such characteristic and non-deducible properties. (1925, pp. 77-78)
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Trans-ordinal laws are what we now call ‘emergent laws,’ fundamental, irreducible laws that describe a synchronic, noncausal covariation of an emergent property and its lower-level emergent base. Emergent laws are not metaphysically necessitated by any lower-level laws, boundary conditions and any lower-level compositional principles. On the epistemological status of emergent laws, Broad comments that:
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- اقتباس :
- There is nothing, so far as I can see, mysterious or unscientific about a trans-ordinal law or about the notion of ultimate characteristics of a given order. A trans-ordinal law is as good a law as any other; and, once it has been discovered, it can be used like any other to suggest experiments, to make predictions, and to give us practical control over external objects. The only peculiarity of it is that we must wait till we meet with an actual instance of an object of the higher order before we can discover such a law; and that we cannot possibly deduce it beforehand from any combination of laws which we have discovered by observing aggregates of a lower order. (1925, p. 79)
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Here we see the unpredictability element of Emergentism that is often discussed. The idea is that even the ideal theorist — Broad's mathematical archangel — with complete knowledge of the lower-level aggregates and properties will be helpless at predicting what might emerge from a specific lower-level structure with certain properties prior to observing the actual instantiation of the complex, higher-level event. This unpredictability, however, is not constitutive of emergence, but rather a consequence of the metaphysical irreducibility of the emergent properties and the trans-ordinal laws they bring in their train.
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