[ JOCR 8.3 (2009) 277-293] (print) ISSN 1476-7430 doi: 10.1558/jocr.v8i3.277 (online) ISSN 1572-5138 DOUBLE PREVENTION AND POWERS by STEPHEN MUMFORD1 University of Nottingham [email protected] and RANI LILL ANJUM University of Tromsø and University of Nottingham [email protected] Abstract. Does A cause B simply if A prevents what would have prevented B? Such a case is known as double prevention: where we have the pre- vention of a prevention. One theory of causation is that A causes B when B counterfactually depends on A and, as there is such a dependence, proponents of the view must rule that double prevention is causation. However, if double prevention is causation, it means that causation can be an extrinsic matter, that the cause and effect need not be connected by a continuous chain of events, that there can be causation by absence, and that there can be causation at a distance. All of these implications jar with strong intuitions we have about the nature of causation. There is, on the other hand, a theory of causation based on an ontology of real dispositions, where causation involves the passing around of pow- ers. This theory in contrast entails that double prevention is not causa- tion and, on this issue, it can claim a victory over the counterfactual dependence account. Keywords: causation, powers, prevention 1 Address for both authors: Department of Philosophy, University of Nottingham, Not- tingham NG7 2RD, UK. © Equinox Publishing Ltd 2009, Unit 6, The Village, 101 Amies Street, London SW11 2JW. 278 STEPHEN MUMFORD & RANI LILL ANJUM Introduction Is A a cause of B simply in virtue of its preventing what would have been a pre- venter of B? Such cases are known as double preventions. They involve the pre- vention of a prevention. What is arguably the leading theory of causation among contemporary analytic metaphysicians – the counterfactual dependence view – rules that double prevention is causation.2 The view has it that A is a cause of B when B counterfactually depends on A, including if it does so via a chain of counterfactual dependencies. This is offered as a reductive analysis. There is nothing more to causation than a counterfactual dependence between events (strictly, the ancestral of the relation of counterfactual dependence: a clause that we hereafter take for granted). Double prevention does seem to involve this kind of counterfactual dependence. Had the ‘cause’, A, not occurred, it would not have prevented something happening that would in turn have pre- vented the ‘effect’ B. If A had not been the case, B would not have been the case. Therefore, for Lewisian theories, double prevention counts as causation. Notwithstanding the appeals of a counterfactual dependence theory of causation, our intuitions on double prevention cases are not so clear cut. There are some grounds on which we feel reluctant to grant double preven- tions as causes. In this paper, those grounds will be explored. It will be argued that, as we have no firm intuitions, it would be wrong to take it for granted that double prevention is causation. On the contrary, if there were to be a theory of causation that could deal with all the standard causal cases but with- out entailing that double prevention is causation, then we should prefer that. There is such a theory, it will be claimed; namely, a theory of causation based on an ontology of real dispositions or causal powers. What is presented here will not be a full argument for the powers view of causation, however. Instead, this paper has the more modest aim of showing that on the issue of double prevention, the powers view produces a more sensible verdict than does the counterfactual dependence view. The powers view rules that double preven- tion for various reasons does not count as causation and thus steers clear of the troublesome consequences that follow from it. Some Examples Lewis’s own example is the simplest. It takes us back to the billiard table that Hume thought offered the ‘perfect instance’ of causation.3 Billiard balls 1 2 D. Lewis, ‘Causation as influence’, in Causation and Counterfactuals, eds J. Collins, N. Hall and L. A. Paul (Cambridge, MA: MIT Press, 2004), 75–106 (84). 3 D. Hume, ‘Abstract of a treatise of human nature’ (1740), in An Enquiry Concerning Human Understanding, ed. P. Millican (Oxford: Oxford University Press, 2007), 133–45. © Equinox Publishing Ltd 2009. DOUBLE PREVENTION AND POWERS 279 and 2 collide. Let us call this collision event A. Had they not collided, ball 1 would have continued its motion and collided instead with billiard ball 3, but such a collision did not happen: it was prevented. Given that the colli- sion between 1 and 3 was prevented, 3 was able to continue on its way, where it met with billiard ball 4 in an event we can call collision B. The situation is depicted in Figure 1.4 Figure 1: Standard double prevention case Collision A, Lewis concludes, is a cause of collision B because B counterfac- tually depends on A. A prevents a preventer of B and thus B counterfactually depends on A. There are other examples of double prevention, away from Hume’s billiard table, that may seem less contrived. Ned Hall gives the example of a bomber that has an escort fighter plane.5 An interceptor is sent to shoot down the bomber but it is prevented from doing so when the fighter gets it first. The bomber is then able successfully to complete its mission and it is arguable that a cause of its doing so was the fighter’s double prevention. The fighter prevented the interceptor from pre- venting the bombing. A third example concerns the causes of a fire. One possible cause is arguably a double prevention. A sprinkler system corrodes, let us assume, and because it does so, it can no longer spray water. A small fire then starts and, because the sprinkler system does not work, the building burns down.6 4 From Lewis, ‘Causation as influence’, 84. 5 N. Hall, ‘Two concepts of causation’, in Causation and Counterfactuals, eds J. Collins, N. Hall and L. A. Paul (Cambridge, MA: MIT Press, 2004), 225–76. 6 D. Davidson, ‘Causal relations’, Journal of Philosophy 64 (1967): 691–703. © Equinox Publishing Ltd 2009. 280 STEPHEN MUMFORD & RANI LILL ANJUM Couldn’t one say that the corrosion in the sprinkler system caused the build- ing to burn down? The corrosion prevented something that could have pre- vented the fire taking hold. Once one starts thinking of examples, one can see that double prevention cases are never hard to find. I may know that I am forgetful, for instance, or just in the middle of a very busy day. I ask someone to remind me of a job I must do if I haven’t already done it by lunch. I am thus, as a safety mea- sure, ensuring that my forgetfulness cannot prevent me from performing the task. I am taking steps to prevent a preventer of a task. If as simple a task as requesting a reminder works through double prevention, then clearly it is a very widespread phenomenon. If Double Prevention is Causation Lewis accepts that double prevention cases are cases of causation. Hence the reminder is a cause of me completing my task, shooting down the intercep- tor is a cause of the bombing, the sprinkler’s corrosion causes the building to burn down and collision A is a cause of collision B. It has to be conceded that there is at least some initial intuitive plausibility to such causal claims. If we probe deeper, however, we see that there are some consequences for cau- sation if we include within it cases of double prevention. Lewis accepts these consequences: that causation need not be an intrinsic matter, that there need be no continuous chain from cause to effect, that there can be causation by absence, and that there can be causation at a distance. It shall be argued that none of these are features we should want in genuine causation and that, if they follow from granting that double prevention is causation, then we should not do so. Why would each of these consequences follow? It is easiest to see why if we consider Lewis’s original billiard table example. In the first place, such causation would not be an intrinsic matter. There is an intuition that whether φ causes ϕ is a matter that concerns only φ and ϕ. Nothing at other times and places should determine whether φ caused ϕ. But now it seems we could have many counterexamples to that. Whether A caused B, in this case, depends on other things. Suppose, for instance, there had been an obstruction on the table between collision A and where billiard ball 1 would have met ball 3. Ball 1 could never, in any case, have collided with 3. Hence we could have collision A occur, and collision B occur, just as before, but now A would not be a cause of B. Because of the obstruction, collision A is now no longer a preventer of a preventer of collision B. Ball 1 could never have done any preventing because the obstruction was in the way. © Equinox Publishing Ltd 2009. DOUBLE PREVENTION AND POWERS 281 Thus we can have two cases exactly the same in respect of the occurrence of A and B, but in one A causes B and in the other it doesn’t. In these two situ- ations, A and B are intrinsic duplicates7 and in the first situation A causes B but in the second situation it doesn’t.8 Second, causation does not require a continuous chain of events from cause to effect.