Emergence occurs when interactions among objects at one level give rise to different types of objects at another level. More precisely, a phenomenon is emergent if it requires new categories to describe it which are not required to describe the behaviour of the underlying components. For example, temperature is an emergent property of the motion of atoms. An individual atom has no temperature, but a collection of them does. Both sides of this debate were confused because they did not fully understand the idea of emergence.
Simulations can provide a powerful metaphor for such theoretical investigations.
There is one important caveat in applying complexity theory to social phenomena. They can all be said to emerge from the actions of individuals. The difference is that while we assume that, for instance, ants have no ability to reason, they just follow instinct and in doing so construct a nest, people do have the ability to recognise, reason about and react to human institutions, that is, to emergent features. It is what makes sociology different from ethology. Not only can we as social scientists distinguish patterns of collective action, but the agents themselves can also do so and therefore their actions can be affected by the existence of these patterns.