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.
Nicolai Hartmann (1882–1950), one of the first modern philosophers to write on emergence, termed this a
categorial novum (new category).
Definitions This concept of emergence dates from at least the time of
Aristotle. In Heideggerian thought, the notion of emergence is derived from the Greek word
poiein, meaning "to make", and 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 illustrate
poiêsis as a threshold event where something moves from one state to another. Many scientists and philosophers have written on the concept, including
John Stuart Mill (
Composition of Causes, 1843) and
Julian Huxley (1887–1975). The philosopher
G. H. Lewes coined the term "emergent" in 1875, distinguishing it from the merely "resultant": 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.
Strong and weak emergence Usage of the notion "emergence" may generally be subdivided into two perspectives, that of "weak emergence" and "strong emergence". One paper discussing this division is
Weak Emergence, by philosopher
Mark Bedau. In terms of physical systems, weak emergence is a type of emergence in which 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 a school of fish, or the formation of galaxies). Crucial in these simulations is that the interacting members retain their independence. If not, a new entity is formed with new, emergent properties: this is called strong emergence, which it is argued cannot be simulated, analysed or reduced.
David Chalmers writes that emergence often causes confusion in philosophy and science due to a failure to demarcate strong and weak emergence, which are "quite different concepts". Some common points between the two notions are that emergence concerns new properties produced as the system grows, which is to say ones which are not shared with its components or prior states. Also, it is assumed that the properties are
supervenient rather than metaphysically primitive. Weak emergence describes new properties arising in systems as a result of the interactions at a fundamental level. However, Bedau stipulates that the properties can be determined only by observing or simulating the system, and not by any process of a
reductionist analysis. As a consequence the emerging properties are
scale dependent: they are only observable if the system is large enough to exhibit the phenomenon. Chaotic, unpredictable behaviour can be seen as an emergent phenomenon, while at a microscopic scale the behaviour of the constituent parts can be fully
deterministic.
Bedau notes that weak emergence is not a universal metaphysical solvent, as the hypothesis that
consciousness is weakly emergent would not resolve the traditional
philosophical questions about the physicality of consciousness. However, Bedau concludes that adopting this view would provide a precise notion that emergence is involved in consciousness, and second, the notion of weak emergence is metaphysically benign. Strong emergence describes the direct causal action of a high-level system on its components; qualities produced this way are
irreducible to the system's constituent parts. The whole is other than the sum of its parts. It is argued then that no simulation of the system can exist, for such a simulation would itself constitute a reduction of the system to its constituent parts. Physics lacks well-established examples of strong emergence, unless it is interpreted as the impossibility
in practice to explain the whole in terms of the parts. Practical impossibility may be a more useful distinction than one in principle, since it is easier to determine and quantify, and does not imply the use of mysterious forces, but simply reflects the limits of our capability.
Viability of strong emergence One of the reasons for the importance of distinguishing these two concepts with respect to their difference concerns the relationship of purported emergent properties to science. Some thinkers question the plausibility of strong emergence as contravening our usual understanding of physics. Mark A. Bedau observes: 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". Strong emergence can be 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: If M is the cause of M∗, then M∗ is overdetermined because M∗ can also be thought of as being determined by P. One escape-route that a strong emergentist could take would be to deny
downward causation. However, this would remove the proposed reason that emergent mental states must supervene on physical states, which in turn would call
physicalism into question, and thus be unpalatable for some philosophers and physicists. Carroll and 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.
Objective or subjective quality 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. The low
entropy of an ordered system can be viewed as an example of subjective emergence: the observer sees an ordered system by ignoring the underlying microstructure (i.e. movement of molecules or elementary particles) and concludes that the system has a low entropy. On the other hand, chaotic, unpredictable behaviour can also be seen as subjective emergent, while at a microscopic scale the movement of the constituent parts can be fully deterministic. ==In science==