Emergence

Emergence plays a central role in theories of integrative levels and of complex systems. For instance, the phenomenon of life as studied in biology is arguably an emergent property of chemistry and physics.

In philosophy

Philosophers often understand emergence as a claim about the etiology of a system's properties. An emergent property of a system, in this context, is one that is not a property of any component of that system, but is still a feature of the system as a whole. Emergent wholes are often described as "more than" or "different to" the sum of their parts.

History

This concept of emergence dates from at least the time of Aristotle. Since then, many scientists and philosophers have written on the concept.

Anglophone philosophy

The first philosophers to use the term "emergent" in its philosophical sense were the "British Emergentists", who characterised life as an emergent phenomenon. This tradition has been dated back to John Stuart Mill's Composition of Causes (1843). In 1875, G. H. Lewes distinguished "emergent" from merely "resultant" phenomena:

Every resultant is either a sum or a difference of the co-operant forces; their sum, when their directions are the same – their difference, when their directions are contrary. Further, every resultant is clearly traceable in its components, because these are homogeneous and commensurable. It is otherwise with emergents, when, instead of adding measurable motion to measurable motion, or things of one kind to other individuals of their kind, there is a co-operation of things of unlike kinds. The emergent is unlike its components insofar as these are incommensurable, and it cannot be reduced to their sum or their difference.

Other philosophers associated with "British Emergentism" include Samuel Alexander, C.D. Broad, and Julian Huxley.

Continental philosophy

Heidegger has been interpreted as referencing emergence with his notion of poiêsis. Derived from the Greek word poiein, meaning "to make", poiêsis refers to a bringing-forth that encompasses not just a process of crafting (techne) but also the broader sense of something coming into being or revealing itself. Heidegger used emerging blossoms and butterflies as examples to describe poiêsis as a threshold event where something moves from one state to another.

Nicolai Hartmann (1882–1950) termed emergence a categorial novum (new category).

Philosophy of mind

An ongoing debate in philosophy of mind concerns the question of whether mental states can be considered emergent properties of the brain. Some philosophers have argued that consciousness is an emergent phenomenon.

Variations

Weak and strong

Usage of the notion "emergence" is often subdivided into two perspectives: "weak emergence" and "strong emergence". Philosopher David Chalmers writes that emergence often causes confusion in philosophy and science due to a failure to demarcate weak and strong emergence, which are "quite different concepts".

Both "weak" and "strong" positions hold that emergent properties are dependent on lower-level phenomena while nevertheless being in some sense autonomous from them.

Weak emergence describes scenarios in which emergent properties, while autonomous, do not introduce novel forces or causes "beyond" their constituent components. A property might count as autonomous if it is the result of interaction rather than aggregation (for example, how the behaviour of an ant colony is produced by exchanges among individuals); if it is sufficient to explain and predict a system (for example, how the path of a tornado can be deduced without reference to its molecular components); or if it can be multiply realised by systems possessing different components (for example, how similar mental states can be produced by different brains). Philosopher Mark Bedau writes that in cases of weak emergence the emergent property is amenable to computer simulation or similar forms of after-the-fact analysis (for example, the formation of a traffic jam, the structure of a flock of starlings in flight, or the formation of galaxies).Although new properties arise in systems as a result of the interactions at a fundamental level, the properties can be determined by observing or simulating the system as a whole, without requiring a reductionist analysis. At large enough scales, seemingly chaotic, hard-to-predict behaviour can emerge, while at a microscopic scale the behaviour of the constituent parts can be fully deterministic.

Strong emergence, by contrast, obtains when a high-level emergent system is autonomous by virtue of being novelly causal, such that it exerts downward influence on its constituent parts. This means that the emergent entity can act on the world in such a way that cannot be deduced from an analysis of the interactive operations of its components. As Chalmers writes, in cases of strong emergence "truths concerning that phenomenon are not deducible even in principle from truths in the low-level domain." Bedau argues that for strongly emergent properties no simulation of the system can exist, for such a simulation would itself constitute a reduction of the system to its constituent parts. The system will evolve in a way that is fundamentally unpredictable, rather than merely difficult to predict.

Subjective and objective

Weak and strong emergence are often described as compatible with "subjective" and "objective" accounts of emergence respectively (sometimes termed "epistemic" and "ontological" emergence). Subjective accounts maintain that emergence requires the impossibility in practice, rather than in principle, to explain the whole in terms of the parts. This position is defended by its advocates on the grounds that it does not imply the appearance of mysterious forces, but simply reflects the limits of individuals' capabilities. Physicist James Crutchfield regards the properties of complexity and organization of any system as subjective qualities determined by the observer:

Defining structure and detecting the emergence of complexity in nature are inherently subjective, though essential, scientific activities. Despite the difficulties, these problems can be analysed in terms of how model-building observers infer from measurements the computational capabilities embedded in non-linear processes. An observer's notion of what is ordered, what is random, and what is complex in its environment depends directly on its computational resources: the amount of raw measurement data, of memory, and of time available for estimation and inference. The discovery of structure in an environment depends more critically and subtly, though, on how those resources are organized. The descriptive power of the observer's chosen (or implicit) computational model class, for example, can be an overwhelming determinant in finding regularity in data.

An observer who could see the precise micro-scale dynamics of every system - such as Laplace's Demon - would not see properties as emergent, as it would understand the exact dynamics giving rise to them. Cognitively limited beings like humans, however, must rely on "coarse-grained" descriptions of the world, and these descriptions can be both predictive and explanatory.

Subjective accounts of emergence are closely related to probability as described in statistical mechanics and Information theory, in which the emergent tendency of entropy to increase over time is a reflection of observers' ignorance of the total system.

Macro-level and micro-level relations

Sean Carroll and Achyuth Parola propose a taxonomy that classifies emergent phenomena by how the macro-description relates to the underlying micro-dynamics.

• Type‑0 (Featureless) Emergence: A coarse-graining map Φ from a micro state space A to a macro state space B that commutes with time evolution, without requiring any further decomposition into subsystems.
• Type‑1 (Local) Emergence: Emergence where the macro theory is defined in terms of localized collections of micro-subsystems. This category is subdivided into:
  • Type‑1a (Direct) Emergence: When the emergence map Φ is algorithmically simple (i.e. compressible), so that the macro behavior is easily deduced from the micro-states.
  • Type‑1b (Incompressible) Emergence: When Φ is algorithmically complex (i.e. incompressible), making the macro behavior appear more novel despite being determined by the micro-dynamics.

• Type‑2 (Nonlocal) Emergence: Cases in which both the micro and macro theories admit subsystem decompositions, yet the macro entities are defined nonlocally with respect to the micro-structure, meaning that macro behavior depends on widely distributed micro information.
• Type‑3 (Augmented) Emergence: A form of strong emergence in which the macro theory introduces additional ontological variables that do not supervene on the micro-states, thereby positing genuinely novel macro-level entities.

Criticisms

Violation of physicalism

Some thinkers propose that emergence contravenes physicalism, and thus common understandings of physics. Mark Bedau observes:

Although strong emergence is logically possible, it is uncomfortably like magic. How does an irreducible but supervenient downward causal power arise, since by definition it cannot be due to the aggregation of the micro-level potentialities? Such causal powers would be quite unlike anything within our scientific ken. This not only indicates how they will discomfort reasonable forms of materialism. Their mysteriousness will only heighten the traditional worry that emergence entails illegitimately getting something from nothing.

The concern that strong emergence does so entail is that such a consequence must be incompatible with metaphysical principles such as the principle of sufficient reason or the Latin dictum ex nihilo nihil fit, often translated as "nothing comes from nothing". For physicalists, the principle of sufficient reason generally implies the causal closure of the physical realm. Strong emergentism seems to violate causal closure by introducing novel causal entities that cannot be accounted for at the microscale. Emergentists may respond to this challenge by embracing a weaker form of emergentism, rejecting physicalism (see substance dualism), or rejecting physical causal closure. Indeed, some thinkers claim that the phenomenon of emergence itself provides evidence against physical causal closure, pointing out that there is precedent in physics for embracing unintuitive conclusions when empirically required.

Overdetermination

Emergence has been criticized for leading to causal overdetermination. The canonical example concerns emergent mental states (M and M∗) that supervene on physical states (P and P∗) respectively. Let M and M∗ be emergent properties. Let M∗ supervene on base property P∗. What happens when M causes M∗? Jaegwon Kim says:

In our schematic example above, we concluded that M causes M∗ by causing P∗. So M causes P∗. Now, M, as an emergent, must itself have an emergence base property, say P. Now we face a critical question: if an emergent, M, emerges from basal condition P, why cannot P displace M as a cause of any putative effect of M? Why cannot P do all the work in explaining why any alleged effect of M occurred? If causation is understood as nomological (law-based) sufficiency, P, as M's emergence base, is nomologically sufficient for it, and M, as P∗'s cause, is nomologically sufficient for P∗. It follows that P is nomologically sufficient for P∗ and hence qualifies as its cause...If M is somehow retained as a cause, we are faced with the highly implausible consequence that every case of downward causation involves overdetermination (since P remains a cause of P∗ as well). Moreover, this goes against the spirit of emergentism in any case: emergents are supposed to make distinctive and novel causal contributions.

If M is the cause of M∗, then M∗ is overdetermined because M∗ can also be thought of as being determined by P. The possibility that emergent phenomena may simply be determined by their base properties is known as the problem of "collapse".

One way in which a defender of emergence could respond to the problem of collapse would be to reject downward causation, and so reject strong emergence. Alternately, a defender strong emergence may reject physical causal closure, and so the account of causation on which Kim's argument rests. Philosopher Carl Gillet has responded to the problem of overdetermination by proposing that emergence is better understood as the introduction of novel causal powers of components of wholes, rather than the wholes themselves.