Causation and Manipulability First published Fri Aug 17, 2001; substantive revision Mon Oct 20, 2008 Manipulablity theories of causation, according to which causes are to be regarded as handles or devices for manipulating effects, have considerable intuitive appeal and are popular among social scientists and statisticians. This article surveys several prominent versions of such theories advocated by philosophers, and the many difficulties they face. Philosophical statements of the manipulationist approach are generally reductionist in aspiration and assign a central role to human action. These contrast with recent discussions employing a broadly manipulationist framework for understanding causation, such as those due to the computer scientist Judea Pearl and others, which are non-reductionist and rely instead on the notion of an intervention. This is simply an appropriately exogenous causal process; it has no essential connection with human action. This interventionist framework manages to avoid at least some of these difficulties faced by traditional philosophical versions of the manipulability theory and helps to clarify the content of causal claims. 1. Introduction A commonsensical idea about causation is that causal relationships are relationships that are potentially exploitable for purposes of manipulation and control: very roughly, if C is genuinely a cause of E, then if I can manipulate C in the right way, this should be a way of manipulating or changing E. This idea is the cornerstone of manipulability theories of causation developed by philosophers such as Gasking (1955), Collingwood (1940), von Wright (1971), Menzies and Price (1993), and Woodward (2003). It is also an idea that is advocated by many non-philosophers. For example, in their extremely influential text on experimental design (1979) Cook and Campbell write: The paradigmatic assertion in causal relationships is that manipulation of a cause will result in the manipulation of an effect. … Causation implies that by varying one factor I can make another vary. [Cook & Campbell, 1979, p. 36, emphasis in original.] Similar ideas are commonplace in econometrics and in the so-called structural equations or causal modeling literature, and very recently have been forcefully reiterated by the computer scientist Judea Pearl in an impressive book length treatment of causality (Pearl, 2000). To a large extent, however, recent philosophical discussion has been unsympathetic to manipulability theories: it is claimed both that they are unilluminatingly circular and that they lead to a conception of causation that is unacceptably anthropocentric or at least insufficiently general in the sense that it is linked much too closely to the practical possibility of human manipulation. (See, e.g., Hausman, 1986, 1998). Both objections seem prima facie plausible. Suppose that X is a variable that takes one of two different values, 0 and 1, depending on whether some event of interest occurs. Then for an event or process M to qualify as a manipulation of X, it would appear that there must be a causal connection between M and X: to manipulate X, one must cause it to change in value. How then can we use the notion of manipulation to provide an account of causation? Moreover, it is uncontroversial that causal relationships can obtain in circumstances in which manipulation of the cause by human beings is not practically possible—think of the causal relationship between the gravitational attraction of the moon and the motion of the tides or causal relationships in the very early universe. How can a manipulability theory avoid generating a notion of causation that is so closely tied to what humans can do that it is inapplicable to such cases? As remarked above, the generally negative assessment of manipulability theories among philosophers contrasts sharply with the widespread view among statisticians, theorists of experimental design, and many social and natural scientists that an appreciation of the connection between causation and manipulation can play an important role in clarifying the meaning of causal claims and understanding their distinctive features. This in turn generates a puzzle. Are non-philosophers simply mistaken in thinking that focusing on the connection between causation and manipulation can tell us something valuable about causation? Does the widespread invocation of something like a manipulability conception among practicing scientists show that the usual philosophical criticisms of manipulability theories of causation are misguided? The ensuing discussion is organized as follows. §§2 and 3 describe two of the best known philosophical formulations of the manipulability theory—those due to von Wright (1971) and Menzies and Price (1993)—and explore certain difficulties with them. §4 argues that the notion of a free action cannot play the central role it is assigned in traditional versions of manipulability theories. §5 introduces the notion of an intervention which allows for a more adequate statement of the manipulability approach to causation and which has figured prominently in recent discussion. §6 considers Pearl's “interventionist” formulation of a manipulability theory and an alternative to it, due to Woodward (2003). §§7 and 8 take up the charge that manipulability theories are circular. §9 returns to the relationship between interventions and human actions, while §10 compares manipulability accounts with David Lewis' closely related counterfactual theory of causation. §§11, 12 and 13 consider the scope of manipulability accounts, while §14 considers some recent objections to such accounts. As we shall see, the different assessments of manipulability accounts of causation within and outside of philosophy derive from the different goals or aspirations that underlie the versions of the theory developed by these two groups. Philosophical defenders of the manipulability conception have typically attempted to turn the connection between causation and manipulability into a reductive analysis: their strategy has been to take as primitive the notion of manipulation (or some related notion like agency or bringing about an outcome as a result of a free action), to argue that this notion is not itself causal (or at least does not presuppose all of the features of causality the investigator is trying to analyze), and to then attempt to use this notion to construct a non-circular reductive definition of what it is for a relationship to be causal. Philosophical critics have (quite reasonably) assessed such approaches in terms of this aspiration (i.e., they have tended to think that manipulability accounts are of interest only insofar as they lead to a non-circular analysis of causal claims) and have found the claim of a successful reduction unconvincing. By contrast, statisticians and other non-philosophers who have explored the link between causation and manipulation generally have not had reductionist aspirations—instead their interest has been in unpacking what causal claims mean and in showing how they figure in inference by tracing their interconnections with other related concepts (such as manipulation) but without suggesting that the notion of manipulation is itself a causally innocent notion. It is the impulse toward reduction that generates the other feature that critics have found objectionable in standard formulations of the manipulability theory. To carry through the reduction, one needs to show that the notion of agency is independent of or prior to the notion of causality and this in turn requires that human actions or manipulations be given a special status-they can't be ordinary causal transactions, but must instead be an independent fundamental feature of the world in their own right. This both seems problematic on its own terms (it is prima-facie inconsistent with various naturalizing programs) and leads directly to the problem of anthropocentricity: if the only way in which we understand causation is by means of our prior grasp of an independent notion of agency, then it is hard to see what could justify us in extending the notion of causation to circumstances in which manipulation by human beings is not possible and the relevant experience of agency unavailable. As we shall see, both von Wright and Menzies and Price struggle, not entirely successfully, with this difficulty. The way out of these problems is to follow writers like Pearl in reformulating the manipulability approach in terms of the notion of an intervention, where this is characterized in purely causal terms that make no essential reference to human action. Some human actions will qualify as interventions but they will do so in virtue of their causal characteristics, not because they are free or carried out by humans. This “interventionist” reformulation allows the manipulability theory to avoid a number of counterexamples to more traditional versions of the theory. Moreover, when so reformulated, the theory may be extended readily to capture causal claims in contexts in which human manipulation is impossible. However, the price of such a reformulation is that we lose the possibility of a reduction of causal claims to claims that are non-causal. Fortunately (or so §§7 and 8 argue) an interventionist formulation of a manipulability theory may be non-trivial and illuminating even if it fails to be reductive.