In system’s theory Emergence is often described as the increasing complexity of a system. While not always clearly defined in the history of the literature, emergence is associated with the notion of downward causation. That is, while upward causation, from lower-level micro phenomena to macro phenomena is usually uncontroversial, the supervenience of macro phenomena on micro phenomena is a more contested claim. The major contention here is with regards to the epistemological or ontological characterization of emergence, and the issue of macro-micro relations, and whether macro-level entities may be reductively characterized in terms of micro level entities. However, if we take emergent entities to be purely consequences of analytic reasoning without ontological significance, they lack any consequential explanatory power and appear to only be mirages of intelligence.

In social theory emergence may be contrasted with methodological individualism, placing social organization (or as Durkheim wrote “social facts”) as levels of organization which explain lower level social behavior and properties. A classic analogy amongst emergence theorists is the distinction between water and its constituting parts: water, though nothing more than the joining of hydrogen and oxygen, displays fluid properties and effects which neither of the two elements does alone. Similarly, Durkheim draws an analogy between the formation of social facts and biochemistry:

But it will be argued that, since the sole elements that make up society are individuals, the primary origin of sociological phenomena can only be psychological. By reasoning in this way, we can just as easily establish that biological phenomena are explained analytically by inorganic phenomena. Indeed, one can be quite certain that in the living cell there are but molecules of crude matter. But these molecules are connected, and it is these connections which cause the new phenomena that characterize life. It is impossible to find even the germ of this connection in any one of these elements. This is because a whole is not the same as the sum of its parts; it is something different, whose properties differ from those displayed by its constituent parts.

(Durkeheim [Thompson], p. 60)