Emergence

The appearance of properties at one level of organisation that the parts do not have and that were not obviously predictable from them.

Theme: Being and reality
Tradition: Modern
Term fixed: 1875

In plain terms

A single water molecule is not wet. Wetness is something a lot of them do together, and there is no smaller amount of water that is slightly wet. Properties like that - real at one scale, absent at the scale below - are called emergent.

The cheap version of this idea is that the whole is more than the sum of its parts, which is true of almost everything and explains nothing. The interesting version asks whether the new property is merely surprising, or whether it is genuinely not derivable from the parts even in principle.

That distinction is the whole subject. If emergence only means we cannot do the calculation, it is a fact about us. If it means the higher level does work the lower level does not fix, it is a fact about the world - and a much harder one to defend.

As a philosopher would put it

The standard division is between weak and strong emergence. Weak emergence: the higher-level property is unexpected and not tractably derivable, but is fixed by the lower-level facts, and simulation is often the only route to it. Strong emergence: the higher-level property is not determined by the lower-level facts at all, and may exert downward causation on them.

Strong emergence is the contested one, because it appears to require either overdetermination or gaps in the lower-level dynamics. Kim's exclusion argument is the standard objection: if every physical event has a sufficient physical cause, a distinct higher-level cause has nothing left to do.

The historical record is not encouraging for strong claims. The British emergentists - Alexander, Morgan, Broad - offered chemical bonding as the paradigm case of a property not derivable from physics, and quantum mechanics derived it within a decade. Consciousness is the case that keeps the position alive, being the one where the derivation has not been produced and where it is disputed whether it could be.

Where you meet it

In 2008 a group at Nagoya University put twenty-two cars on a single-lane circular track 230 metres round and asked the drivers to hold thirty kilometres an hour and keep an even distance.

For a short time it worked. Then small fluctuations - a driver braking slightly, the one behind braking a little harder - amplified into a full stop-and-go wave that travelled backwards around the ring at about twenty kilometres an hour while the cars continued forwards. There was no obstacle, no accident, no bottleneck and no bad driver. Sugiyama and colleagues published the result, and the footage is the clearest demonstration of a phantom jam ever produced.

The wave is a real object. It has a position, a speed and a direction, all different from any car's. It is entirely made of drivers doing ordinary things, none of whom is doing anything wave-like, and nothing about a single driver would let you predict it. Whether that makes it emergent in any strong sense is exactly the argument - the wave is fully determined by the cars, and it is still the right thing to talk about.

What is actually disputed

Whether strong emergence is coherent.

Reductionists hold that every apparent case is either weak emergence or an unfinished explanation, and point to the record: the British emergentists chose chemistry as their example, and chemistry fell. On this view emergence tracks the limits of current derivation, which is a fact about the state of science.

Against that, the exclusion argument's premise - that the physical is causally closed - is itself contested, and the demand that higher-level properties earn their keep by being derivable may set the bar in a place no special science could clear, including ones nobody doubts. Consciousness remains the hard case in both directions: the one property for which no derivation exists and about which reasonable people disagree whether one is even possible.

Commonly confused with

the whole is more than its parts True of almost anything and empty as it stands. The claim only has content once you say whether the extra is unpredictable in practice or undetermined in principle.

Defined against

Determinism Strong emergence claims the lower level does not fix the higher, which is where the two questions meet

Philosophers

Alfred North Whitehead Novelty as basic to process rather than an anomaly in it
Henri-Louis Bergson Creative evolution, and the argument that novelty is real
John Stuart Mill The distinction between homopathic and heteropathic effects, which is the idea before the word
Karl Raimund Popper Emergence defended against the reductionist programme

Works

Creative Evolution Real novelty, argued against mechanism
The Conscious Mind The case that consciousness will not reduce
Consciousness Explained The case that it will
The Logic of Scientific Discovery The methodological background to the reduction dispute

Schools

Process Philosophy Where novelty is fundamental
Vienna Circle Where the unity of science and reduction were the programme
Atomism The picture emergence claims is incomplete
Pittsburgh School (Sellarsian Realism) Where levels of description are taken seriously without dualism

Related concepts

Change c. 500 BC · Relationality c. 150 · Causation c. 330 BC · Explanation 1948 · Consciousness 1641

The term is George Henry Lewes's, in 1875, distinguishing emergent from resultant effects; the British emergentists of the 1920s made it a position, and it was largely abandoned when quantum chemistry explained the cases it rested on.