The idea of a causal power has been appealing to the realist tradition within the philosophy of science, and especially so for the philosophy of social science. Proponents of this idea include Nancy Cartwright (Nature’s Capacities and Their Measurements), Margaret Archer (Realist Social Theory: The Morphogenetic Approach), and Dave Elder-Vass (The Causal Power of Social Structures). Elder-Vass provides a succinct description of the tradition:

Bhaskar offers us an alternative way of understanding causality, a causal powers theory. This draws on a different, realist, tradition of thinking about cause, one that goes back at least as far as Aristotle, but one that has been less influential than the covering law model in twentieth-century social science. As [Ruth] Groff puts it, ‘realists about causality think, contra Hume, that causal relations are relations of natural or metaphysical necessity, rather than of contingent sequence’ — and that this necessity arises from the nature of the objects involved in those causal relations (Groff 2008:2-3). (43)

Stephen Mumford and Rani Lill Anjum’s Getting Causes from Powers is an important contribution to this debate. Here are several useful comments from Mumford’s contribution to the The Oxford Handbook of Causation, “Causal Powers and Capacities”:

Where it is most radical, the powers ontology proposes a major reconceptualization of causation. Hume, as traditionally interpreted, understood the world to consist of distinct and discrete, unconnected existences. If this is accepted, then the best that can be made of causation is that it is a contingent and external relation between such existences. The powers ontology accepts necessary connections in nature, in which the causal interactions of a thing, in virtue of its properties, can be essential to it. Instead of contingently related cause and effect, we have power and its manifestation, which remain distinct existences but with a necessary connection between. One such tradition was based in Britain and came from the work of Rom Harré (1970; 2001, and with Madden 1973; 1975), which seems to have been an influence on Roy Bhaskar (1975) and Nancy Cartwright (1983; 1989; 1999). In Cartwright, the commitment is to capacities, which in her account differ from dispositions in that they ‘are not restricted to any single kind of manifestation … [but] can behave very differently in different circumstances’. (1999: 59)

Putting the point simply, the assertion that an entity has a causal power comes down to a claim about the nature of the entity and the strong dispositional properties that this nature gives rise to. Sugar has the causal power to stimulate the taste of sweetness in typical human subjects; this power derives from the chemical structure of the sugar molecule and the micro-organization and functioning of taste receptor neurons. A magnet has a power to attract a piece of iron, in virtue of its microstructure. In each case we have identified a real feature of the entity, and this feature is a consequence of real properties of its microstructure.

This approach makes sense with regard to social structures and institutions as well. If paramilitary organizations have a propensity to create young adherents who are easily mobilized in support of fascist politics (as argued by Michael Mann in Fascists), then we can make reference to this causal power in our explanation of the rise of Italian fascism. University X’s tenure system produces a teaching environment in which students get little attention from their faculty, as a consequence of the incentives and habits it cultivates in young faculty. This means something fairly straightforward: given the specific arrangements associated with this tenure system, the interactions that individuals have within this institution inculcate patterns of behavior that bring about the consequence. On this story, “producing a faculty climate that gives little priority to undergraduate students” is a causal power of this institutional arrangement. Change the internal arrangements and you get different causal properties.

In the case of the social world, however, the fundamental constituents of social powers are the constrained and developed actions of persons who act within the context of a given set of institutions and structures. Unlike the iron magnet, whose powers derive from identical iron atoms arranged in certain geometries, a tenure institution or a safety organization derives its properties from the structured actions of the individuals who compose it.

The rationale for asserting necessity in either the natural or the social realm — the idea that the power is a real property of the thing — is the theory of scientific realism: things actually have the causal powers we observe because they have an inner constitution that propels their interactions with other entities. So the causal relation is a kind of necessary relation, not just a brute fact about regularities. Metals conduct electricity because of the chemical-physical structure of the copper wire. And universities have the properties they possess because of the institutional arrangements they embody and the actions of individuals within those arrangements.

So the theory of causal powers doesn’t have to presuppose an objectionable form of metaphysical essentialism. Instead, it can be a defensible framework for embodying the idea of causal realism: things have the causal properties and dispositions they have in virtue of their micro-composition.

Why is it useful to use the language of causal powers? Because we can encapsulate a large amount of the pertinent causal properties of an entity into a fairly simple set of expectations. If iron is magnetic (a causal power) we can derive a large number of expectations about its behavior in a variety of circumstances; and we can explain those circumstances based on the powers we have empirically or theoretically established. If a certain kind of regulatory organization is observed to have the causal power of “contributing to an abnormal number of accidents” — then one part of an explanation of a particular accident may be the fact that it occurred within the scope of that kind of regulatory organization. (Charles Perrow offers an argument along these lines in Normal Accidents: Living with High-Risk Technologies.)