Causal Factors, Causal Inference, Causal Explanation

s from how likely it is that the person is a smoker in the first place. More generally, the trouble is that the likelihood principle aims to by-pass decisions about prior probabilities. Perhaps there are some inferential contexts where such decisions can sensibly be avoided. But the inference from Harry's heart attack to his smoking isn't one of them. (From a Bayesian point of view, if in addition to knowing that Prob(H/S) = . 9, we know that Prob(H) = . 1 and that Prob(S) = 1/106, then Harry's heart attack should make us believe that he smoked to the degree 9/106. ) What about the second case, where we know that Harry both smoked and had high cholesterol, and want to know which of these his heart attack was actually due to? Here the likelihood principle might seem to make more sense. We don't have to This content downloaded from 207.46. 13.85 on Tue, 23 Aug 2016 05:37:44 UTC All use subject to http://about.jstor. org/terms 126 II-DAVID PAPINEAU worry about prior probabilities, because we know that the causal factors are both present. Surely then the sensible thing is to assign the result to the cause that makes the most difference? But I don't accept the presupposition that the heart attack must be due either to the smoking or to the high cholesterol. As I have it, there are actually four possibilities in the single case: the background factors then present allow smoking to make a difference, but not high cholesterol; the background factors allow high cholesterol to make a difference, but not smoking; the background factors allow both to make a difference; the background factors allow neither to make a difference. All four possibilities are left open by the fact that smoking and high cholesterol are population causes of heart attacks. And I don't see how we can reach any conclusions about the single case without some further assumptions about the structure of background causes. Thus, for instance, if we believe that heart attacks are an indeterministic phenomenon, we will be likely to assume (though we won't have to) that both smoking and high cholesterol increase the chance of heart attacks for all sets of background conditions. And this will incline us to judge that Harry's smoking and his high cholesterol are both (part of) what caused his heart attack. On the other hand, if we think that heart attacks are always determined, then we will think that smoking only makes a difference given certain very specific background conditions (namely, given conditions together with which smoking determined a heart attack); and we will think the same about the conditions required for cholesterol to make a difference. And so in Harry's case we will probably think that his heart attack is due either to his smoking, or to his high cholesterol, but not to both. My way of reading the question of whether Harry's heart attack is due to his smoking or to his high cholesterol is different from Sober's. From my point of view, this question only arises when we are ignorant of certain facts about the particular case. We know that there are certain background factors in conjunction with which smoking makes a difference, and we know that there are certain background factors in conjunction with which high cholesterol makes a difference; but we don't know what those background factors are, and so we don't know whether Harry has them or not. If we did know what they were, This content downloaded from 207.46. 13.85 on Tue, 23 Aug 2016 05:37:44 UTC All use subject to http://about.jstor. org/terms CAUSAL FACTORS, INFERENCE AND EXPLANATION 127 and whether Harry had them, then we would know what difference Harry's smoking and his high cholesterol made to the chance of his heart attack in the actual circumstances, and then we would know whether his smoking, or his high cholesterol, or both, were single-case causes of his heart attack. Sober, however, thinks that there is a further fact of the matter about what 'token caused' Harry's heart attack, even after we know all the probabilistically relevant facts about the particular case. It seems initially plausible to say that, even if smoking is a property cause of heart attacks, there is still a further question as to whether Harry's smoking caused Harry's heart attack. But I suspect that is because we read this as the question: were Harry's actual circumstances such as to allow his smoking to make a difference to his chance of a heart attack? This latter question is a good question, and one we might still want to ask even after we know that smoking is a population cause of heart attacks. But it's not Sober's question. For it's fully answered once we know all the probabilistic facts about the single case, whereas Sober's question is supposed to depend on some yet further fact of the