One of the important exponents of a structure-centered approach to social theory is Anthony Giddens. His 1979 book, Central Problems in Social Theory: Action, Structure, and Contradiction in Social Analysis, is one place where his views on structure are expressed. He separates himself from earlier versions of "structuralism," including Saussure and Levi-Strauss; but he advocates for the reality of social structures and the methodological appropriateness of attempting to arrive at empirically based theories of social structures in sociology and other areas of the social sciences. He emphasizes the fact of process rather than static organization in his theory of structures; to capture the "verbiness" of a process view, he prefers the language of "structuration" rather than "structuralism." This distinction having to do with the location of things in time -- a static snapshot versus a continuous process -- extends to his treatment of action as well:
'Action' or agency, as I use it, thus does not refer to a series of discrete acts combined together, but to a continuous flow of conduct. We may define action... as involving a 'stream of actual or contemplated causal interventions of corporeal beings in the ongoing process of events-in-the-world'. (55)A recent and unapologetic treatment of the reality of social structures is presented in Dave Elder-Vass's The Causal Power of Social Structures (2010). Elder-Vass accepts the point that agency and structure are inseparable; neither functions as a solely sufficient cause of social outcomes. But he argues strongly for the idea that social structures have causal powers that are not reducible to facts about individuals. He places his analysis generally within the tradition of critical realism (Bhaskar, A Realist Theory of Science). And he relies heavily on the theory of supervenience to solve the riddle of how structures can be composed of individual-level activity and yet possess autonomous causal powers (Kim, Mind in a Physical World: An Essay on the Mind-Body Problem and Mental Causation).
Elder-Vass rejects the ontology of methodological individualism, which he regards as a species of reductionism: social properties need to be reducible to features of individuals. And yet he fully and unambiguously embraces the obvious fact that social structures must be composed of individuals in relations to each other. His way out of this apparent contradiction is to argue that social structures possess emergent causal powers: causal characteristics that pertain to the whole but not to the parts or their ensembles. Here is how he characterizes emergence:
A thing ... can have properties or capabilities that are not possessed by its parts. Such properties are called emergent properties. (4)And later:
An emergent property is one that is not possessed by any of the parts individually and that would not be possessed by the full set of parts in the absence of a structuring set of relations between them. (17)It is obvious and unexceptional that there are "emergent" properties in this limited sense. However, I'm not sure it captures the full concept of emergence. It would appear that holists have another idea in mind as well: the idea that the properties of the whole cannot be derived from knowledge of the properties of the parts and their relations to each other. ((E-V discusses this angle under the topic of "eliminative reductionism"; 24, 54.) A square figure is composed of four lines; the figure possesses area, whereas the lines do not. Sugar is sweet, but its component parts -- carbon, hydrogen, oxygen -- are not. So is "sweetness" an emergent property? Apparently it is not; because the sweetness of the compound can in fact be explained by the knowledge we have of the chemistry of the components, their molecular bonds, and the human sensors that register "sweetness." The property of sweetness can be derived from knowledge of the basic chemistry and the workings of the sensory system. So sweetness can be "reduced" to facts about the molecule and the sensor. It is not a novel causal power.
Here is why Elder-Vass thinks the concept of emergence is valuable in the context of social structures:
The value of the concept of emergence lies in its potential to explain how an entity can have a causal impact on the world in its own right: a causal impact that is not just the sum of the impacts its parts would have if they were not organised into this kind of whole. (5)But really his central insight is that composites may have causal powers that are relatively autonomous from the powers of their parts:
Reductionist thinkers have argued that if we can explain how a causal power works in terms of lower-level forces, the original power itself becomes redundant to any explanation of its effects. By contrast, I argue in chapter 3 that when we explain a causal power, we do not explain it away. (6)And here is his central point:
I shall argue that social entities [structures] are causally effective in their own right, with causal powers that are distinct from those of human individuals. But I shall also examine the mechanisms that underpin these causal powers, thus recognizing the contributory role that human individuals make to the functioning of social structures. (6)(This last point is what I and others refer to as providing "microfoundations" for claims about social causation.)
So this seems to be Elder-Vass's core ontology of structures: structures are composed of individuals in relation to each other; structures have "emergent" causal powers that are not simply the sum of the causal powers of the component individuals; these emergent powers derive from the relations between the components; and for any particular causal power of the structure it must be possible to provide an explanation of the power in terms of mechanisms involving the individuals and their relations.
The bulk of the book takes the form of an effort to work out this view in detail with respect to two important types of social structures: organizations and normative circles. A bank is an organization (which in turn fits into a web of other organizations). A normative circle is a set of overlapping sets of individuals who both embody and conform to a normative rule or ideal. (E-V traces the idea here back to Durkheim and Simmel.) More on this later!
I suggested above that the concept of explanatory autonomy might work better than emergence. So what is a good definition of "relative autonomy" of causal powers at one level or another, with respect to the underlying entities? I think there are many areas of the sciences where we identify a set of causal processes that are sufficiently regular and predictable, that we don't feel obliged to drop down to the next level in order to achieve an adequate explanation. A level is "explanatorily autonomous" if entities at that level conform to a regular set of causal relations. Thinking of the brain as a computing system is an example. If we analyze the visual system in terms of a set of receptors, aggregators, detectors, analyzers, etc., and if this model allows us to explain and predict the organism's perceptual capacities (including mistakes), then we don't need to have a full theory of the neurophysiology that underlies. On this example, "perception as computational system" is relatively autonomous with respect to the underlying neurophysiology.