An interesting article on Understanding Society discusses strong and weak microfoundationalism in sociology. I’d never encountered the term before but I’m definitely a weak microfoundationalist in Daniel Little’s sense. I don’t believe explanation must proceed in terms of individuals but I think all social explanation must be consistent with the properties and powers of relevant individuals.
Microfoundation is something like this: an account of the mechanisms at the individual actor level (and perhaps at levels intermediate between actors and the current level — e.g. institutions) that work to create the structural and causal properties that we observe at the meso or macro level. A fully specified microfoundational account of a meso-level feature consists of an account that traces out (1) the features of the actors and (2) the characteristics of the action environment (including norms and institutions) which jointly lead to (3) the social pattern or causal power we are interested in. A microfoundation specifies the individual-level mechanisms that lead to the macro- or meso-level social fact. This is the kind of account that Thomas Schelling illustrates so well in Micromotives and Macrobehavior.
My adherence to microfoundationalism today is a little bit weaker still. I now advocate a version of microfoundationalism that specifies only that we must be confident (an epistemic concept) that such micro-to-macro relations exist. We must be confident there are such mechanisms but not obliged to specify them. (I also hold that the best ground for having that confidence is being able to gesture plausibly towards roughly how they might work.) Another way to put it is this requirement: “No magical thinking!” That is, we exclude explanations that would only be possible if we assumed action at a distance, blocks of wood that have complicated mental lives, or intelligent beings with infinite computational faculties. A convincing way of discrediting a meso-level assertion is to give an argument that it is unlikely that real human agents would in fact act in ways that lead to this meso-level situation. (Example: Chinese planners who created the collective farming system in the Great Leap Forward assumed that collective farms would be highly productive because a “new socialist man” would emerge. This was unlikely, and therefore the individual behavior to be expected on collective farms would lead to “easy riding” and low productivity.)
So the ontological principle is simply that social entities are wholly fixed by the properties and dynamics of the actions of the actors that constitute them. The requirement of microfoundations simply reproduces the ontological principle, ruling out ontologically impossible relations among social entities. The requirement of microfoundations is not a requirement on what an explanation needs to look like; rather, it is a requirement about certain beliefs we need to be justified in accepting when we advance a claim about social entities. It is what JZ calls a “confirmation” requirement (or perhaps better, a justificatory requirement). A better theory of the actor supports the discovery of microfoundations for social assertions. Further, it provides a richer “sociological imagination” for macro- and meso-level sociologists. So the requirement of microfoundations and the recommendation that social scientists seek out better theories of the actor are also valuable as heuristics for social research: they provide intellectual resources that help social researchers decide where to look for explanatory links, and what kinds of mechanisms might turn out to be relevant.