Most critical realists would probably think that their philosophy of social science is flatly opposed to ontological individualism. However, I think that this opposition is unwarranted.
Let's begin by formulating a clear idea of ontological individualism. This is the view that social entities, powers, and conditions are all constituted by the actions, thoughts, and mental frameworks of individual human beings, and nothing else. The social world is constituted by the socially situated individuals who make it up. This is not to question the undoubtable fact that individuals have social properties -- beliefs, values, practices, habits, and relationships -- that are integral to their consciousness and agency. But these properties themselves are the recursive effects of prior sets of socially constituted, socially situated individuals who have contributed to their formation as social actors. Fundamentally, then, social entities are constituted by individual actors; and individual actors have in turn been framed, shaped, and influenced by their immersion in prior stages of social arrangements and relationships.
Consider a trivial illustration of the kind of recursive individual-social-individual process that I have in mind here. Consider the habit and norm of queuing in waiting for a bus, boarding a plane, or buying a ticket to a popular music concert. Queuing is not a unique solution to the problem of waiting for something. It is also possible for individuals within a group of people to use their elbows and voices to crowd to the front in order to be served earlier. But in some societies or cultural settings children have been given the example of "waiting your turn", lining up patiently, and conforming to the norms of polite fairness. These norms are internally realized through a process of socialization and maturation, with the result that the adult in the queuing society has both the habit and the norm of waiting for his or her turn. Further, non-conformists who break into the queue are discouraged by comments, jokes, and perhaps a quick jab with a folded umbrella. In this case adults were formed in their social norms by the previous generation of teachers and parents, and they in turn behave according to these norms and transmit them to the next generation. (Notice that this norm and behavior differs from the apparently similar situation of bidding on a work of art at an auction; in the auction case, the individuals do not wait for their turn, but rather attempt to prevail over the others through the level, speed, and aggressiveness of their bids.) Here we might say that the prevailing social norms of queueing-courtesy are a social factor that influences the behavior of individuals; but it is also evident that these norms themselves were reproduced by the prior behaviors and trainings offered by elders to the young. Further, the norm itself is malleable over time. If the younger generation develops a lower level of patience through incessant use of Twitter and cell phones, rule breakers may become more common until the norm of queueing has broken down altogether.
This example illustrates the premises of ontological individualism. The queueing norm is promulgated, sustained, and undermined by the various activities of the individuals who do various things throughout its life cycle: accept instruction, act compliantly, instruct the young, deviate from the norm. And the source of the causal power of the norm at a given time is straightforward as well: parents and teachers have influence over the behavior of the young, observant participants in the norm have some degree of motivation towards punishing noncompliant individuals, and ultimately other sources of motivation may lead to levels of noncompliance that bring about the collapse of the norm altogether.
Several points are worth underlining. First, ontological individualism is fully able to attribute causal powers to social assemblages, without being forced to provide reductionist accounts of how those powers derive ultimately from the actions and thoughts of individuals. OI is not a reductionist doctrine. Second, OI is not "atomistic", in the sense of assuming that individuals can be described as purely self-contained psychological systems. Rather, individuals are socially constituted through a process of social formation and maturation. This person is "polite", that person is "iconoclastic", and the third person is deferential to social "superiors". Each of these traits of psychology and motivation is a social product, reflecting the practices and norms that influenced the individual's formation. (This isn't to say that there is nothing "biological" underlying personality and social behavior.)
Several points can be drawn from this account. First, OI is not a reductionist doctrine -- any more than is "physicalism" when it comes to having a scientific theory of materials. We do not need to derive the properties of the metal alloy from a fundamental description of the atoms that constitute it. Second, OI is not an atomistic doctrine; it does not postulate that the constituents of social things are themselves pre-social and defined wholly in terms of individual characteristics. In a perfectly understandable sense the socially constituted individual is the product of the anterior social arrangements within which he or she developed from childhood to adulthood. And third, OI does not compel us to take an "as-if" stance on the question of the causal properties of social assemblages. The causal powers that we discover in certain kinds of bureaucratic organization are real and present in the world -- even though they are constituted and embodied by the actions, thoughts, and mental frameworks of the social actors who constitute them.
Now let's turn to critical realism and the position its practitioners take towards "individualism" and the relationship between actors and structures. Roy Bhaskar addresses these issues in The Possibility of Naturalism.
First, the ontological question about the relationship between "actors" and "society":
The model of the society/person connection I am proposing could be summarized as follows: people do not create society. For it always pre-exists them and is a necessary condition for their activity. Rather, society must be regarded as an ensemble of structures, practices and conventions which individuals reproduce or transform, but which would not exist unless they did so. Society does not exist independently of human activity (the error of reification). But it is not the product of it (the error of voluntarism). Now the processes whereby the stocks of skills, competences and habits appropriate to given social contexts, and necessary for the reproduction and/or transformation of society, are acquired and maintained could be generically referred to as socialization. It is important to stress that the reproduction and/ or transformation of society, though for the most part unconsciously achieved, is nevertheless still an achievement, a skilled accomplishment of active subjects, not a mechanical consequent of antecedent conditions. This model of the society/ person connection can be represented as below. (PON, 39)
This is a complicated statement. It affirms society exists as an ensemble of structures that individuals "reproduce or transform" and that "would not exist unless they did so". This is the key ontological statement: society depends upon the myriad individuals who inhabit it. The statement further claims that "society pre-exists the individual" -- that is, individuals are always born into some set of social arrangements, practices, norms, and structures, and these social facts help to form the individual's agency.
Here is the diagram to which Bhaskar refers (PON 40):
It seems, then, that Bhaskar's view is fundamentally similar to the view of methodological localism developed in earlier posts (link, link, link). Methodological localism affirms that there are large social structures and facts that influence social outcomes. But it insists that these structures are only possible insofar as they are embodied in the actions and states of socially constructed individuals. The “molecule” of all social life is the socially constructed and socially situated individual, who lives, acts, and develops within a set of local social relationships, institutions, norms, and rules. And these supra-individual structures and norms are, in turn, maintained by the actors who inhabit them.
Francesco Di Iorio addresses many of these points in his contribution to Research Handbook of Analytical Sociology through his analysis of the relationship between critical realism and methodological individualism. Much of Di Iorio's analysis seems entirely correct. But, following Bhaskar, Di Iorio seems to postulate the absolute (temporal) priority of the social over the individual; and this seems to be incorrect.
According to critical realists, MI cannot account for the fact that the social world and its bounds exist independently of the individual interpretation of this world, that is, independently of the individual’s opinion about what she is free or not free to do. (Di Iorio 141)
It seems apparent, rather, that the relationship between the social world and the particular constitution of human actors at a given time is wholly recursive: social arrangements at ti causally influence individuals at ti; actions and transformations of individuals at ti+1 lead to change in social arrangements in ti+1; and so on. So neither social arrangements nor individual constitution are temporally prior; each is causally dependent upon the other at an earlier time period.
So it seems to me that there is nothing in the core doctrines of critical realism that precludes a social ontology along the lines of ontological individualism. OI is not reductionist; rather, it invites detailed investigation into the ways in which social arrangements both shape and are shaped by individual actors. And these relationships are sufficiently complex and iterative that it may be impossible to fully trace out the connections between surprising features of social institutions and the underlying states of the actors who constitute them. As a practical matter we may have confidence about beliefs about the properties of a social structure or institution, without having a clear idea of how these properties are created and reproduced by the individuals who constitute them. In this sense the social properties are weakly emergent from the individual-level processes -- a conclusion that is entirely compatible with a commitment to ontological individualism (link).
One of the most prominent critics of ontological individualism is Brian Epstein. His arguments are considered in earlier posts (link, link, link). Here is the conclusion I draw from his negative arguments about OI in the supervenience post:
Epstein's analysis is careful and convincing in its own terms. Given the modal specification of the meaning of supervenience (as offered by Jaegwon Kim and successors), Epstein makes a powerful case for believing that the social does not supervene upon the individual in a technical and specifiable sense. However, I'm not sure that very much follows from this finding. For researchers within the general school of thought of "actor-centered sociology", their research strategy is likely to remain one that seeks to sort out the mechanisms through which social outcomes of interest are created as a result of the actions and interactions of individuals. If Epstein's arguments are accepted, that implies that we should not couch that research strategy in terms of the idea of supervenience. But this does not invalidate the strategy, or the broad intuition about the relation between the social and the actions of locally situated actors upon which it rests. These are the intuitions that I try to express through the idea of "methodological localism"; link, link. And since I also want to argue for the possibility of "relative explanatory autonomy" for facts at the level of the social (for example, features of an organization; link), I am not too troubled by the failure of a view of the social and individual that denies strict determination of the former by the latter. (link)
It is evident that the concept of microfoundations has a close relationship to ontological individualism. Here are several efforts at reformulating the idea of microfoundations in a more flexible way (link, link). And here are several effort to provide an account of "microfoundations" for practices, norms, and social identities (link, link). This line of thought is intended to provide greater specificity of the recursive nature of "structure-actor-structure" that is expressed in the idea of methodological localism.