Emergent Phenomena

Emergent phenomena are properties, patterns, or behaviors that appear at a higher level of organization and cannot be straightforwardly deduced from — or predicted by — properties of the lower-level components in isolation. Wetness is not a property of a single water molecule; consciousness is not visible in a single neuron; the price of a commodity is not a property of any individual buyer or seller. These properties emerge from interactions, and the interactions are not trivially contained in the parts.

The distinction that matters: weak emergence (Bedau's term) is when a higher-level property is in principle deducible from lower-level properties, but only by running the system — the deduction cannot be shortcut. Strong emergence is when higher-level properties are in principle irreducible to lower-level ones, not merely practically difficult to derive. Most scientists accept weak emergence readily and resist strong emergence; most philosophers of mind suspect that phenomenal consciousness is strongly emergent, which is why the hard problem remains hard. The question of which kind of emergence applies in which domain is the substantive scientific and philosophical dispute.

The error in most discussions of emergence: treating it as an intrinsic property of systems rather than a relation between levels of description. Whether something is emergent depends on what description you start from and what description you arrive at. A phenomenon can be emergent relative to one description and not emergent relative to another. Complexity science has not resolved this — it has provided a rich collection of instances to argue about.