Abstract
I consider backtracking reasoning: that is, reasoning from backtracking counterfactuals such as if Hitler had won the war, he would have invaded Russia six weeks earlier. Backtracking counterfactuals often strike us as true. Despite that, reasoning from them just as often strikes us as illegitimate. A number of diagnoses have been offered of the illegitimacy of such backtracking reasoning which invoke the fixity of the past, or the direction of causation. I argue against such diagnoses, and in favor of one that invokes a principle I call the fixity of reasons. Backtracking reasoning violates the fixity of reasons. But, the fixity of reasons is a principle that must be observed in order to engage in practical reasoning at all.
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Notes
I am using ‘backtracking conditional’ in a somewhat stipulative way. Sometimes ‘backtracking conditional’ seems to be used without any implication of temporal priority. Used in this second way the antecedent is dependant on the consequent in the same sense in which the consequents of non-backtracking conditionals depend on their antecedents. Sometimes ‘backtracking conditional’ is used with an implication of temporal priority different from the one I have in mind. So used, it is enough for a conditional to backtrack that the time of its consequent is earlier than the time of its antecedent. On this third use a conditional may backtrack even if its antecedent and consequent are both future. As I am using ‘backtracking conditional’, unless otherwise specified, a conditional backtracks only if its consequent is past relative to the time it is employed in practical reasoning.
What of the subjunctive conditional B’s indicative counterpart: If I, Conscientious, do go away, the exam has not been scheduled? For most of the paper I focus on the way in which subjunctive backtrackers enter into practical reasoning. What I have to say about that will provide the stage setting for a complementary story about backtracking indicatives and practical reasoning. Telling it will have to wait for another occasion
Fisher (1994, p. 95)
Lewis ibid, p. 33
That the deliberator has been so informed is a feature of each of the examples of backtracking reasoning we have considered so far. But, as Mark Heller has pointed out to me, it is an inessential feature. What matters is the availability to the deliberator of the information about the occurrence of the relevant past event. Here, in the end, is what I would want to defend. Availability, like rationality, comes in degrees. Backtracking reasoning is irrational to the extent that the information about the non-occurrence of the event mentioned in the backtracker is available to the one engaging in backtracking reasoning. The backtracking reasoning in each of the so far mentioned cases is manifestly irrational because the information about the relevant past event is readily available to the reasoner.If that is correct, it has the following bearing on Newcomb's Problem. In that case, the one-boxer engages in backtracking reasoning. Consider the following Newcomb variations: (a) The deliberator is participating in a Newcomb situation. Moreover, when it comes time to choose, no one knows whether Box 1[the box opaque to the deliberator] is empty, or contains $1M. (b) Like (a), except that the deliberator knows that every one of a large number of one boxers have ended up with an empty Box 1. (c) Like (a), except that the deliberator knows someone in the audience can see the contents of the box opaque to her, (d) The combination of (b) and (c). (e) The deliberator can clearly see what Box 1 contains. What should we say about the rationality of being a one-boxer in each of these situations? Here is what I would say. It is more rational to be a one boxer in (a) that in any of (b)–(e). It is less rational to be a one boxer in (e) than any of (a)–(d) Moreover, it is more rational to be a one boxer in (b) or (c) than in (d). If you agree with these assessments, what was said at the beginning of this footnote provides the start of an explanation. As we move from (a) to (b) or (c) the information about the predictor's choice is more available to the deliberator, but less so than in (d). In (e) the information about the predictors choice is as available as it could be to the deliberator.
Suppose he does not. Suppose the case of Jim and Jack is redescribed to make explicit that Jim has, at the time of deliberating, no possibility of epistemic access to the past quarrel. In that case the example would fail to meet one of the stipulated conditions. Jim would lack even a prima facia reason to accept the backtracker: if I, Jim, were to ask Jack for a loan, there would have been no quarrel yesterday.
In reaching this conclusion Conscientious is relying on the assumption that transitivity holds for mixtures of forward and backtracking counterfactuals. She appears to be reasoning to B* from B together with: If the exam had not been scheduled, I would not have received a letter informing me that it has. Transitivity inferences from mixtures of forward and backward tracking counterfactuals are notoriously problematic. So, we may think that there is an explanation of the irrationality of backtracking reasoning in the offing separate from the fixity of the past. Such reasoning involves an illegitimate application of transitivity to mixtures of forward and backward tracking conditionals. Call this the transitivity explanation.In section 4 I will present two science fictional cases [but, I will argue, none the worse for that]. The second case defeats the transitivity explanation.
At any rate, they are competing under the assumption that the irrationality at issue is not over determined.
The time of the consequent of (iii) is earlier than the time of the antecedent, but not earlier than the time it enters into Annette's practical reasoning
See footnote 8.
I am indebted to an anonymous referee for calling my attention to this alternative
References
Downing, P. B. (1959). Subjunctive conditionals, time order, and causation. Proceedings of the Aristotelian Society, 59, 125–140.
Fisher, J. M. (1994). The metaphysics of free will: an essay on control. Oxford: Blackwell.
Lewis, D. (1986). Counterfactual dependence and time’s arrow. Philosophical papers volume II (pp. 32–66).
Acknowledgements
I am indebted to all those who have commented on the paper. I am especially indebted to Mark Heller for his penetrating observations.
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Gallois, A.N. The fixity of reasons. Philos Stud 146, 233–248 (2009). https://doi.org/10.1007/s11098-008-9253-x
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DOI: https://doi.org/10.1007/s11098-008-9253-x