contrastive rational explanation of free choice

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Contrastive Rational Explanation of Free ChoiceAuthor(s): Randolph ClarkeSource: The Philosophical Quarterly, Vol. 46, No. 183 (Apr., 1996), pp. 185-201Published by: Oxford University Press on behalf of the Scots Philosophical Association and theUniversity of St. AndrewsStable URL: http://www.jstor.org/stable/2956386 .

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The Philosophical Quarterly, Vol. 46, No. 183 April 996 ISSNooq? -8o94

CONTRASTIVE RATIONAL EXPLANATION OF FREE CHOICE

BY RANDOLPH CLARKE

If we assume the libertarian view that a choice is free only if it is not causally determined by prior events, is it possible to provide a contrastive rational explanation of a free choice, a rational explanation, for example, of why a

given agent chose the alternatives he did rather than others which he was considering? The question is often answered negatively. Alternatively, it is sometimes held that, while non-causal contrastive rational explanation of an undetermined free choice is possible, causal contrastive rational explanation is not. I shall argue here that the libertarian requirement of indeterminism is no bar to the causal contrastive rational explanation of free choice. Even given that libertarian requirement, it will often be possible to explain causally why an agent made one choice rather than another by appealing to the reasons on the basis of which the agent made the choice.

Enquiry into the availability of contrastive rational explanation is often driven by concern over whether it is possible for an agent to act with the control requisite for libertarian freedom. I shall close the paper by questioning whether these two issues are so closely related. In my view, we may have adequate contrastive rational explanation along with indeterminism, but that neither rules out nor implies, nor is implied by, libertarian control.

I. TWO NAY-SAYERS

Thomas Nagel maintains that a free choice would have to be one that was not causally determined by prior events, and he holds that the appropriate sort of rational explanation of a free choice would be a non-causal explanation.' Such an explanation, which Nagel calls an 'intentional explanation', explains in terms of 'justifying reasons and purposes' and is 'comprehensible only through [the agent's] point of view' (p. 115). It is precisely the job of an

' T. Nagel, The Viewfrom Nowhere (Oxford UP, I986).

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I86 RANDOLPH CLARKE

intentional explanation to explain (contrastively) why the agent made the choice he did rather than the alternative that was causally open to him. However, since it might have happened that, even with the same reasons, the agent made the alternative choice, no intentional explanation will be able to provide a contrastive explanation.

When someone makes an autonomous choice such as whether to accept a job, and there are reasons on both sides of the issue, we are supposed to be able to explain what he did by pointing to his reasons for accepting it. But we could equally have explained his refusing the job, if he had refused, by referring to the reasons on the other side - and he could have refused for those other reasons: that is the essential claim of autonomy. It applies even if one choice is significantly more reasonable than the other. Bad reasons are reasons too (pp. 1 5-I6).

Intentional explanation can non-contrastively explain either choice, should it be made. 'But for this very reason it cannot explain why the person ac- cepted the job for the reasons in favour instead of refusing it for the reasons against' (p. 116). It might be observed, Nagel adds, that the agent's reasons for choosing as he in fact did were themselves reasons against choosing otherwise for different reasons; but the same could have been said had the agent chosen otherwise. No such observation will 'stave off the question why these reasons rather than the others were the ones that motivated [him]' (p. II7). No intentional explanation will answer that question; it will either remain unanswered or be answered in terms of'formative causes of ... character or personality' (ibid.). And the availability of a contrastive explanation of this latter sort, Nagel implies, is inconsistent with libertarian freedom.

Robert Kane disagrees with Nagel about the availability of non-causal contrastive rational explanations of libertarian free choices.2 On Kane's view, such choices may contrastively rationally explain themselves. The event that is the making of the choice, he maintains, may be described in either of two ways: as a cognitive event (coming to believe that certain reasons are the better ones); and as a volitional event (intentionally term- inating an effort of will for those reasons). 'One can answer the question of why it occurred under one description by citing it under another description, and vice versa' (PPR I989 p. 246). But he argues that no causal contrastive rational explanation of such a choice is possible.

According to Kane (pp. 240-I), 'the paradigm cases of undetermined free choices are those involving inner struggle and effort of will which must be exercised against countervailing inclinations'. Two important kinds of these are

2 R. Kane, Free Will and Values (State Univ. of New York Press, 1985); 'Libertarianism and Rationality Revisited', Southern Journal of Philosophy, 26 (I988), pp. 44I-60; 'Two Kinds of Incompatibilism', Philosophy and Phenomenological Research, 50 (i989), pp. 219-54; 'Free Will: the Elusive Ideal', Philosophical Studies, 75 (1994), pp. 25-60.

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CONTRASTIVE RATIONAL EXPLANATION OF FREE CHOICE 187

cases of moral struggle, involving conflict between reasons or motives of duty and reasons of self-interest; and cases of prudential struggle, involving conflict between desires for one's own long-range good and desires for one's own present good. In either kind of conflict, the agent's view of which reasons ought to prevail is in doubt, and the agent makes an effort of will 'directed at getting one's ends (purposes, intentions) sorted out' (p. 234). The indeterminism derives from the fact that the effort of will is of indeterminate strength; it might result in one's resisting temptation, and it might result in one's failing to resist. In either case,

the agent's character and motives could explain the occurrence of the effort on the part of the agent without explaining the outcome of the effort, i.e., the choice itself, because the choice ... would not be determined (p. 236).

The fact that the outcome of the effort of will is not causally determined prevents us from contrastively explaining the choice by citing, as a non- deterministic cause of the choice, the agent's having certain reasons:

the effort of will that terminates in choice one way or the other is indeterminate. One could not predict the outcome even if one knew all one could know about the prior facts. Nor could one explain the critical difference - the choosing of A rather than choosing otherwise, or vice versa - in terms of past circumstances and laws of nature

(pp. 244-5).

In these passages, then, Kane assumes that a choice can be causally contrastively explained only if that choice was causally determined. We shall see whether this assumption is warranted.

II. CAUSAL CONTRASTIVE EXPLANATION

The most detailed account of causal contrastive explanation of events in

general is that advanced by Peter Lipton.3 Lipton models his account on Mill's method of difference, which is employed in the discovery of causes. When we have a case in which a certain effect occurs, and a second, similar case in which it does not, the method of difference tells us that we may locate a cause if we discover an antecedent that is present in the first case but absent in the second. * Lipton proposes the following 'difference condition' as an adaptation of Mill's method to the task of providing contrastive explanations:

: P. Lipton, 'Contrastive Explanation', in D. Knowles (ed.), Explanation and its Limits (Cambridge UP, I990); 'Contrastive Explanation and Causal Triangulation', Philosophy of Science, 58 (I99I), pp. 687-97; Inference to the Best Explanation (London: Routledge, I99I), to which most citations below refer; 'Making a Difference', Philosophica, 51 (I993), pp. 39-54.

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I88 RANDOLPH CLARKE

To explain why p rather than q, we must cite a causal difference between p and not-q, consisting of a cause of p and the absence of a corresponding event in the history of

not-q (Inference to the Best Explanation p. 43).

A corresponding event is, roughly, 'something that would bear the same relation to q as the cause ofp bears to p' (p. 44). A causal difference, then, is an event that caused p and bears a certain relation R to p such that in the actual course of events there is no occurrence that would have borne that same relation R to q, had q occurred. As will emerge below (?IV), not every causal difference has contrastive explanatory relevance: we have a contrastive explanation only when the relation in question is explanatorily relevant.

(I shall take this further requirement for granted for the time being and return to it later.) Nevertheless, Lipton maintains, the discovery of a causal difference between the fact p and the foil q is an essential first step in providing a causal contrastive explanation.

Suppose, for example, thatJones has syphilis, while Smith does not. Un- treated syphilis develops into paresis in only a small proportion (about 28%) of cases, but paresis never occurs otherwise. Suppose that Jones develops paresis. In the causal process leading to that development there is an event, Jones' having syphilis, that has no corresponding event in the process leading to Smith's not developing paresis; Smith does not have syphilis. We

may explain why Jones rather than Smith developed paresis by citing this causal difference, by saying thatJones had syphilis.

Now there are no known determinants of whether a patient with untreated syphilis will contract paresis; so far as is known, the causal process from one condition to the other may be non-deterministic. (I shall take it for

granted that non-deterministic causation is possible: Nagel does not reject it and Kane affirms it.) Yet this does not undermine the explicability of the contrast in question. Even if the causal process is genuinely not deterministic, it seems clear that Jones' having syphilis explains why he rather than Smith came down with paresis. For a contrastive question such as 'Why did Jones rather than Smith get paresis?' takes it as given that one ofJones and Smith contracted the disease and asks why that one was Jones. An answer

citing a causally necessary condition that obtained in Jones' case but not in Smith's thus adequately answers the question. The example indicates, then, that contrastive explanations may be available for non-deterministically caused events, and even for events that were improbable given all ante- cedents.

The paresis example presents us with two different actual outcomes of two numerically distinct, albeit similar, causal processes. But we sometimes

request or offer a contrastive explanation of the occurrence of one rather

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than another possible outcome of a single causal system. The difference condition may be applied to this second sort of contrast as well, and again it

appears to allow for contrastive explanation of non-deterministically caused events. Here is an example:

The bubonic plague bacillus (Yersinia pestis) will, if left to develop unchecked in a

human, produce death in 50% to 90% of cases. It is treatable with antibiotics such as

tetracycline, which reduce the chance of mortality to between 5% and io%.4

Even given these statistics, it could be that the causal processes involved in death by bubonic plague or recovery following antibiotic treatment are deterministic. But it is not known that they are, and let us suppose that these

processes are genuinely non-deterministic. Suppose that Alice has been infected by the bacillus and then treated with an appropriate antibiotic; and

suppose that she survives. Compare Alice with Bob, who was infected by the bacillus, received no treatment, and died. It appears that we can explain why Alice rather than Bob survived: she received antibiotic treatment. Her survival resulted from a treatment that left the likelihood of that outcome at close to i; and the administration of the antibiotic, in virtue of being a highly effective survival-promoting treatment, bears an explanatorily relevant relation to her survival that nothing in the actual history would have borne to Bob's survival, had he survived. And now it seems just as plausible that we can explain, again by citing the administration of the antibiotic, why Alice survived rather than died. For again, had she died, nothing in the actual

history would have borne the same explanatorily relevant relation to that outcome as the treatment bore to her survival; she received no treatment that left the likelihood of her death at close to i. If we have a contrastive

explanation in this case, then it can sometimes be explained why a non- deterministic process produced one outcome rather than another that it

might have produced. The preceding considerations do not establish that it is sometimes possible

to provide a causal contrastive explanation of an undetermined event; but they do render that thesis plausible, and suggest that Lipton's account is close to the truth about how and when it is possible. It is sometimes said

flatly that when an event is not causally determined, it cannot be contrastively explained. Perhaps what lies behind this rejectionist position is the view that to explain contrastively is to cite an event or condition given which the outcome had to occur. But the paresis case seems to be a clear disproof of the rejectionist position. Thus the view that a contrastive explanation must cite an event or condition given which the explanandum event had to occur

The example is drawn from P. Humphreys, The Chances of Explanation (Princeton UP, 1989), p. ioo, though it is there used for a different purpose.

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I90 RANDOLPH CLARKE

appears mistaken, and Lipton's account receives support because its verdict agrees with the judgement we are inclined to make in this sort of case.

Moreover, it is sometimes held that whenever a single causal process might produce either of two or more mutually incompatible results, the actual result cannot be contrastively explained. But here we must be careful. In one sort of case, an indeterministic causal process might result in effect e,, and it might instead result in effect e2, and whichever of el or e2 results will have all and only the same causes as the other possible result would have had, had it resulted. In a case of this sort, it appears that there is indeed no causal contrastive explanation of the outcome. However, it also appears that the difference condition will agree with this judgement; for in such a case it does not appear that any cause of the actual result will lack a corresponding event in the history of the non-occurrence of the alternative result. On the other hand, in another sort of case, an indeterministic causal process might result in e,, and it might instead result in e2, and whichever of e, or e2 occurs will have some causes that would not have been causes of the other possible result, had that other result occurred. Alice's case is of this sort. The bacillus is not a cause of her survival; and had she died, the antibiotic would not have been a cause of her death. It is less plausible to say in a case of this sort that there is no causal contrastive explanation of the outcome. Given the difference between this sort of case and those where either outcome would have the same causes, and given the plausibility that Lipton's account gains from the accord between it and plausible judgements in cases involving two actual outcomes of two distinct causal processes, it seems to me that the burden of argument lies on those who would reject Lipton's account and its verdict in the sort of case in question.

Lipton's account of causal contrastive explanation thus looks quite pro- mising. However, as it stands, it has a few shortcomings. Chief among these is the fact that the important notion of an explanatorily relevant relation that the cited causal difference bears to the fact p is left unexplained. I shall have nothing to say about the general notion of explanatory relevance, though later in the paper I shall offer some suggestions regarding back-

ground principles that help determine explanatorily relevant relations when it is a choice that is being explained.

Second, Lipton claims that on his account an explanation of why p rather than not-p cannot be provided along the same lines as explanations of other contrasts. For, he argues (p. 49), the difference condition would have us look for a cause ofp that is absent in the history of not-not-p; but since not-not-p would seem just to be p, no such event could be found. If Lipton is right about this, then that appears to be a drawback of the account, since it would be preferable to treat all causal contrastive explanation in a unified way.

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CONTRASTIVE RATIONAL EXPLANATION OF FREE CHOICE I19

However, it seems to me that Lipton is mistaken here. Granted, his formulation of the difference condition tells us that to explain why p rather than not-p we must find a 'causal difference' between p and p (not-not-p). However, when we see what a causal difference is said to be (in terms of a 'corresponding event'), it emerges that the problem is one of a misleading formulation, not one of an inapplicable principle. The causal difference in

question need not be an event that is present in the (causal) history ofp but absent from the history of p. Rather, it must be some cause ofp that bears a certain relation R to p, such that no event that actually occurred in the history of p would have borne R to not-p had the actual outcome not occurred. And an event fitting this description may indeed be available.

We may see this point by comparing what Lipton says (p. 44) about the application of the difference condition to a case where we explain why a single causal system had one outcome p rather than another q:

The condition does not require that the same event be present in the history of p but absent in the history of not-q, a condition that could never be satisfied when the two histories are the same, but only that the cited cause of p find no corresponding event in the history of not-q where, roughly speaking, a corresponding event is something that would bear the same relation to q as the cause ofp bears to p.

Substitute 'not-not-p' (or 'p') for 'not-q', and 'not-p' for 'q', and we have an explanation of how the difference condition applies to the explanation of why p rather than not-p.

To illustrate, suppose that Alice was infected by bubonic plague bacillus and received an antibiotic treatment that raised her chances of recovery to 0.95. Suppose that she did indeed recover. Why did she recover rather than not recover? The difference condition requires us to find a cause of Alice's recovery that bears a certain relation R to her recovery (and, moreover, that relation must be explanatorily relevant), such that in the actual history of Alice's recovery there is no event that would have borne R to Alice's not recovering, had she failed to recover. But it is not impossible to find such an event. Alice's recovery resulted from her receiving a treatment that left the probability of her recovery at close to I. But had she not recovered, no event in the actual history would have borne such a relation to that outcome. For she received no treatment that similarly promoted her not recovering. It is a virtue of Lipton's account, then, that it can handle the contrast 'p rather than not-p' in the same way as it handles other contrasts.

Finally, I shall consider an objection to Lipton's account that requires, I think, a minor refinement. In a slightly different version of the paresis example, both Smith andJones have untreated syphilis, but onlyJones con- tracts paresis. We could not then explain why Jones rather than Smith contracted paresis. However, if the difference condition is clearly to rule out

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192 RANDOLPH CLARKE

a contrastive explanation in such a case, then the notion of the 'history' of not-q must be clarified. Critics (e.g., Grimes5) as well as supporters of Lipton, and sometimes even Lipton himself (e.g., p. 44) take the history of not-q to be the causal history of not-q. But as Grimes points out (p. 32), Smith's syphilis is not a (contributing) cause of Smith's not having paresis; Smith is free of paresis despite his syphilis. Thus Smith's syphilis is not in the causal history of his not having paresis. The difference condition may thus appear to be satisfied, forJones' having syphilis is a cause of his contracting paresis, and in the causal history of Smith's not contracting paresis there is no event

corresponding toJones' having syphilis. (And although, as I have indicated, Lipton does not intend the difference condition as a sufficient condition for contrastive explanation, it is clear from his discussion that he regards it as ruling out an explanation of whyJones rather than Smith contracted paresis in the case where Smith had syphilis.)

The solution, I think, is to allow the 'history' of not-q to be broader than the causal history of that outcome.6 Such a reading is suggested by Lipton's reference (p. 44) to Smith's 'medical history'. And the looser sense of the history of not-q is consistent with the explication of a corresponding event as

something in the actual course of events that would have borne the same relation to q (had q occurred) as the event cited in the explanans bears to p. I shall work with the difference condition understood in this manner.

III. CAUSAL CONTRASTIVE RATIONAL EXPLANATION

The application of Lipton's account to the causal contrastive rational

explanation of choice is straightforward. Suppose that Sue is considering whether to go for a bike-ride or not. She has reasons for and against going. She carefully considers these various reasons, and then she judges, in the light of her reasons, that it would be better to go for a ride. On the basis of this judgement, and on the basis of the reasons for which she made this

judgement, she chooses to go for a ride, and she does so. Why did she choose to ride her bike rather than choosing not to ride it? Because she

judged, in the light of her reasons, that going for a bike-ride would be better. There is a cause of Sue's choosing to go for a ride - her judging that going for a ride would be better - that lacks a corresponding event in the history of her not choosing not to go for a ride. Or, more simply, the judgement that she actually made caused and bears an explanatorily relevant relation to her

T. Grimes, 'Explanatory Understanding and Contrastive Facts', Philosophica, 51 (1993), pp. 21-38.

' Lipton informs me that he has independently made such a revision in the paperback edition of his book.

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actual choice that no actual occurrence would have borne to her choosing not to go, had she made that alternative choice. Citing this causal difference

rationally explains the contrast in question. It thus appears possible, at least in some cases, to provide a causal con-

trastive rational explanation of why an agent chose a certain alternative rather than another that he was considering. And, given what we have seen in the previous section, it appears possible to provide such an explanation even if the causal process that produced the choice was non-deterministic. For suppose that, even given her judgement that going for a ride would be better, it remained causally open to Sue to choose not to go. (For the time

being, suppose that the judgement rendered it highly probable that she would choose to go for a ride; the significance of this last supposition will

emerge in the next section.) It is then false that, given her judgement, it had to happen that she choose to go. Still, it seems that her judging that going for a ride would better explain why she chose to go rather than not. For that

judgement causes and rationalizes her actual choice in a way in which no actual occurrence would have rationalized the alternative choice. And

people generally choose what they judge to be better. (I shall have more to

say on this point too in the next section.) Unlike the contrastive rational explanation that Nagel tries out and

rejects (the agent's reasons for making the choice actually made were also reasons against making the alternative choice for the reasons favouring it), the contrastive rational explanation of Sue's choice given here would not have explained the alternative choice, had she made it. If Sue had chosen not to go for a bike ride, she would have been choosing contrary to her

judgement regarding which alternative was better, and hence we could not have truly said that she so chose because she judged that not going for a ride would be better. There might have been available a contrastive explanation different from the one that was available for the actual choice; or there

might not have been available any true contrastive explanation. We nevertheless co'ild have non-contrastively explained her irrational choice by citing the reasons for which she made it.

It thus appears that a causal contrastive rational explanation can do something that Nagel claims that an autonomous intentional explanation is

supposed to do but cannot, namely, explain why the agent made one choice rather than another that was causally open. Nagel, of course, recognizes that in some situations, 'one choice is significantly more reasonable than the other' (p. I 6); but he fails, I think, to see how that fact may play a role in an

explanatory scheme that agrees, as Lipton's does, with many of our judgements about contrastive explanations.

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I94 RANDOLPH CLARKE

Nagel sometimes writes as though the contrast that needs to be explained is not why the agent made one choice rather than another but why certain reasons rather than others motivated the agent. In Sue's case, we may have an answer to this second contrastive question as well: perhaps Sue has a

strong standing disposition to be motivated by the reasons favouring the alternative that she has judged, in the light of her reasons, to be better. It

might then be asked why Sue possesses rather than lacks such a disposition, to which, if there is an answer, it would seem to be one in terms of 'formative causes of ... character or personality' (p. 117). Nagel appears to think that since the chain of explanation has led us to such external factors - factors over which, presumably, Sue has never had any control - the

explanation that we started out with is not of the sort needed for free choice. However, the availability of this contrastive explanation in terms of 'formative causes' is consistent with 'the essential claim of autonomy' - that, even

given her character and her reasons (including her judgement concerning which alternative was better), it remained open to Sue to choose not to go for a bike-ride. For we may have a chain of contrastive explanations, culminating in a contrastive rational explanation of a choice, even when

given all the factors cited by those explanations the eventual choice did not have to occur.

Likewise, we might ask why Sue judged, in the light of her reasons, that

going for a bike-ride would be better, rather than judging, in the light of those reasons, that not going for a ride would be better. To this question there may be the answer that going for a ride was far better supported by her reasons, and Sue is rational enough to be able, upon reflection, to see when an alternative is far better supported by her reasons. It might then be asked why Sue is of such a character rather than otherwise, to which, if there is an answer, it will presumably be in terms of 'formative causes of her character or personality'. But again the availability of this chain of contrastive explanations is consistent with its having remained open to Sue to make the alternative choice. I shall return to this point in the final section of the paper.

Sue's case differs from the sorts of cases that concern Kane, for in those, prior to the making of the choice, the agent makes no unequivocal judgement regarding which alternative is better. I shall delay until the next section discussion of the explanation of choice in these kinds of cases. How- ever, we can already see that Kane's assumption that a causal contrastive

explanation will be available only for a choice that is causally determined is mistaken with respect to at least some cases. The requirement that a free choice must be undetermined is not in general any bar to causal contrastive rational explanation of free choice.

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IV. ADDITIONAL PRINCIPLES OF SELECTION

Lipton offers the difference condition as a necessary condition for causal contrastive explanation; it is not held to be sufficient. It may happen, he allows, that some event that is a cause ofp and that finds no corresponding event in the history of not-q nevertheless does not explain why p rather than

q. In other words, there may be some event that causes p and bears a certain relation R to p, such that no event that actually occurred would have borne R to q had q occurred, and yet such that citing it may in no way explain why p resulted rather than q. This may happen when the relation R is of no

explanatory relevance. Thus, as Lipton notes (p. 47), some principles of selection of contrastively explanatory factors in addition to the difference condition are required. What more is needed is some account of which causal differences have contrastive explanatory relevance.

The need is easily enough seen with respect to rational explanation of choice, in a case of what we may call rational indeterminacy. Edna wants an afternoon snack, and consequently she walks down the hall to the vending machine. Of the several items in the machine, only two interest her: the chocolate bar and the tortilla chips. The bar, Edna thinks, would be good and sweet, the chips good and salty. Neither would be better than the other. Edna chooses to buy the chocolate bar, and she does so. Although her choice was not uniquely rational - an alternative would have been just as rational - Edna's choice was not in any respect rationally deficient. We can

provide an adequate rational explanation of it by citing her taste for chocolate. Moreover, we can explain why she chose the chocolate bar rather than certain other items in the machine: she saw something good in the bar, but she did not see anything good in them. However, it does not appear that we can explain why Edna chose the chocolate bar rather than the tortilla

chips. (Here I assume that the reasons favouring these two options were of

relatively equal motivational strength; I discuss the relevance of motivational

strength below.) Yet, there is a causal difference (of sorts) between her

choosing the bar and her not choosing the chips: she thought the bar would be sweet, while she did not think that about the chips. But a causal difference of this sort does not provide even a poor explanation of the contrast in

question. Lipton (pp. 47-8) suggests three general principles of selection from

among causal differences. First, someone who asks a contrastive question may already know about some causal differences; a good explanation will indicate some further difference. Second, we generally prefer an explanation

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I96 RANDOLPH CLARKE

that cites a corresponding event that would have brought about the foil q had it (the corresponding event) occurred. Finally, we often prefer an explanation that cites an event that was causally necessary for the fact p in the circumstances.

However, as Lipton recognizes, none of these further principles determ- ines necessary conditions for contrastive explanation. The last does not apply to the explanation of why Alice rather than Bob survived; and the second does not apply to the explanation (in the first paresis example) of whyJones rather than Smith contracted paresis. As for the first, an enquirer may be aware of a certain causal difference but fail to see that that factor explains the outcome.

I have no proposal concerning general principles of contrastive explanatory relevance which, when added to the difference condition, would yield a complete account of contrastive explanation. I doubt that there are such general principles. But there may be principles of explanatory relevance that apply to specific contexts, and in particular there may be such principles that apply to the context of human choice.

What we need is some account of background principles governing the rational explanation of choice. I suggest that there are two such principles: (a) that every (sane) human agent has a strong standing disposition to choose rationally - an agent who has judged, in the light of his reasons, that a certain alternative is best, is thus strongly disposed to choose on the basis of the reasons favouring that alternative; and (b) that every human agent tends to choose on the basis of the motivationally strongest reasons relevant to the choice at hand. (By 'motivational strength', I mean causal strength, or the degree to which the reasons contribute to the probability that the agent will make the choice and perform the action favoured by those reasons.) Each principle expresses a loose connection between choice and a certain kind of strength of reasons. Although agents may have a strong standing disposition to choose rationally, on given occasions they may be more strongly disposed to choose contrary to their judgements of what would be best to do. And although agents tend to choose on the basis of their motivationally strongest reasons, if choices are not causally determined, then on some occasions they may choose on the basis of motivationally weaker reasons.7

Together the two principles provide a crucial part of the background of our understanding of human choice, and it is in the light of this background that we seek and offer rational explanations of choice. (I believe that similar background principles apply to the contrastive rational explanation of overt action that is not preceded by choice, and it would be a simple matter to

7For defences of this, see R. Clarke, 'Doing What One Wants Less', Pacific Philosophical Quarterly, 75 (1994), pp. i-I ; A. Mele, Autonomous Agents (Oxford UP, 1995), ch. 3, esp. p. 41.

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extend my argument to such cases.) This suggests that there are at least two main kinds of case in which a causal difference may contrastively rationally explain a free choice. The first kind is composed of cases where an agent chooses rationally. Here, a causal difference, consisting, for example, in the agent's judging in the light of his reasons that a certain alternative is best, may explain why he chose that alternative rather than any other he was considering. Sue's case is one of this kind. We explain why she chose to ride her bike rather than choosing not to ride it by noting that she judged, in the light of her reasons, that going for a ride would be better.

In a case of what Kane calls prudential struggle, the agent makes no unequivocal judgement regarding which alternative is better (nor, as Kane puts it, regarding which reasons are better) prior to making the choice. Nevertheless, when the agent chooses prudently, the background principle that human agents have a strong standing disposition to choose rationally suggests that we may explain why the agent made this choice rather than the other by citing his judgement that this option best promotes his long- term interests. For the pursuit of present interests at the expense of (acknowledged) greater long-term interests is irrationally imprudent.

For a second main kind of case, suppose that Sue had chosen not to go for a bike-ride despite having judged that going riding would be better. Sup- pose that her reasons not to go riding were motivationally much stronger. Then a causal difference consisting in the agent's having motivationally much stronger reasons for making a certain choice than she has for making any alternative may explain why the agent made that choice rather than any alternative. Sue chose not to go riding rather than choosing to go riding because her reasons against going riding were motivationally much stronger.

Similarly, when in cases of what Kane calls prudential struggle an agent chooses contrary to what he regards as his long-term interests, if the reasons on the basis of which he chooses are motivationally much stronger, then we may explain why he made the imprudent choice rather than the prudent by citing the greater motivational strength of the reasons for which he made his choice. Contrastive explanations of choices in cases involving moral struggle may likewise be available when the agent chooses on the basis of his motivationally stronger reasons. I doubt, however, whether there is a third

background principle to the effect that human agents have a strong standing disposition to choose morally; for it seems that where self-interest is at stake, we are at least as likely to choose selfishly.

The contrastive explanations offered in these cases seem to me correct; if they are, that supports the suggestion that the two principles in question help to select from among causal differences those that are explanatory. However, a third main kind of case remains to be considered, ones where an

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I98 RANDOLPH CLARKE

agent chooses rationally but contrary to his motivationally strongest reasons. The fundamental question here is whether it is possible to explain causally and contrastively a free choice that was less probable than some alternative given all prior conditions.

Suppose, for example, that Sue's reasons not to go bike-riding were motivationally stronger than her reasons to go riding, though she judged the latter alternative to be better, and she chose that alternative. It may still be correct to say that she chose to go riding rather than choosing not to go because she judged going riding to be better, but I am uncertain about this

point. One thing that does seem clear is that there is no sharp distinction of

adequacy with respect to relative probability. A choice that was only slightly less probable than the most probable alternative may be nearly as adequately contrastively explicable as is a choice that was only slightly more

probable than the next most probable alternative. There is a related question whether it is possible to explain causally and

contrastively a choice that was improbable given all prior conditions. As above, so here it strikes me as plainly arbitrary to say, for example, that only a choice that was more likely than not to be made (i.e., that had a probability greater than 0.5) can be causally contrastively explained.8 For in a case in which the probability that the agent will make a certain choice is

minutely less than 0.5, as compared with a case where the probability that the agent will make a certain choice is minutely greater than 0.5, is there really any sharp distinction with respect to which choice, once it is made, can be causally contrastively explained? It seems to me that there is plainly no sharp distinction here. The point is even stronger if we suppose that the agent who made the slightly improbable choice made it on the basis of a

judgement that that choice was far and away the better option, while the agent who made the slightly more probable choice chose highly irrationally. It would seem absurd to say that the first agent's choice cannot be causally contrastively explained but the second agent's choice can be.

Moreover, even the claim that there is a distinction of degree between improbable and highly probable choices with respect to how adequately they can be contrastively explained must be carefully qualified. For the contrastive explicability of an outcome varies with the contrast in question. In the first paresis example, where Jones but not Smith had syphilis, we can explain why Jones rather than Smith contracted paresis, even though, we are supposing, the probability ofJones' getting paresis was quite low. How- ever, it does not appear that we could explain whyJones contracted paresis rather than not contracting it, and the improbability of his getting it is a factor in rendering such an explanation unavailable.

K As is said by R. Double in, e.g., The Non-Reality of Free Will (Oxford UP, I991), pp. 202-9.

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The situation would appear to be the same when it comes to explaining choices. Suppose that Carl and Dave are both trying to choose from among several compact disc players. Carl reads about a new brand that he had not previously known about; Dave remains uninformed of the existence of that brand. Suppose that, even given his knowledge of the new brand, it remains improbable that Carl will choose to buy it, but he chooses to do so. Since, we may suppose, there was no chance that Dave would choose to buy a brand that he did not know existed, the causal difference between Carl's choosing to buy the new brand and Dave's not choosing to seems to explain why Carl rather than Dave made that choice. But Carl's knowledge of the new brand does not seem to explain why he chose that one rather than not choosing it.

Even in saying this last, however, we have to be careful. For suppose that, although it remained improbable that Carl would choose to buy the new brand, that choice was significantly more likely than any other particular alternative. In that case, for each alternative, citing Carl's reasons favouring the new brand may explain, in an adequate way, why he chose that brand rather than the alternative. In sum, even if there is a distinction of degree with respect to adequate contrastive explicability between highly probable and improbable choices, it does not appear to be at all simple.

Finally, even if there is such a distinction and there is no adequate answer to some contrastive questions about choice, it will still be possible to provide adequate non-contrastive causal explanations of improbable choices. In the case of an improbable rational choice, such an explanation will be a causal rational explanation of the choice. In the event of an improbable irrational choice, the explanation will be a causal reasons-explanation, though the reasons it cites will not render the choice rational in the context. These non-contrastive causal explanations of choice do not get worse as the probability of the choice to be explained declines. For the adequacy of a non-contrastive causal explanation of an undetermined event is unaffected by how probable that event was.9

V. 'ULTIMATE EXPLANATION'

I have argued that causal contrastive rational explanations can do something that Nagel claims intentional explanations cannot do, and that Kane is

9 See R. Clarke, 'A Principle of Rational Explanation?', Southern Journal of Philosophy, 30, no. 3 (1992), pp. I-I2. For defence of the claim that improbable events can be (non- contrastively) causally explained just as adequately as can highly probable events, see (e.g.) Humphreys pp. I09-I7; W. Salmon, Scientific Explanation and the Causal Structure of the World (Princeton UP, 1984), pp. 84-9.

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200 RANDOLPH CLARKE

mistaken about the availability of causal contrastive rational explanations of undetermined choices. However, it must be noted that the contrastive rational explanations that I claim to be available will not satisfy Nagel and Kane. If a choice is free, they both maintain, then there will be a rational

explanation of it that is 'final' or 'ultimate', in the sense that what is cited in the explanans is not further explicable by anything beyond the agent's reasons.'0 Such ultimate rational explicability is held to be necessary if the agent is to have the variety of control over the making of a choice that con- stitutes free will. But the explanations that I claim to be available are not ultimate, for the causal factor that they cite may be further explained by citing others, and these may be further explained by citing yet others, and so on, until the causal factors cited are not reasons possessed by the agent and not events over which the agent has ever had any sort of control. Thus, in

Nagel's and Kane's views, the contrastive rational explanations that I claim to be available are not adequate for free choice.

Although this line of thought is widespread, it is, I believe, quite mistaken. One possible source of error has already been touched upon. The fact that a chain of contrastive explanation of a choice leads back to a contrastive

explanation that cites factors over which the agent has never had any control would seem to undermine freedom if (and, so far as I can tell, only if) the availability of the latter explanation implied that, given the factor cited, the eventual choice had to occur. But we have seen, I think, that the

availability of causal contrastive explanations of choice implies no such

thing. Thus, the availability of the sorts of contrastive explanations I have discussed appears consistent with libertarian freedom.

Perhaps Nagel and Kane believe that, although such explanations are consistent with libertarian free choice, they are not enough. We may think of the matter this way. There is a certain increase in control, or a change from a lesser variety of control to a greater variety, when we move from an unfree choice to a (libertarian) free choice. Nagel and Kane apparently assume that the increase in agent-control, or the change from a lesser variety to a greater variety, implies the availability of a different kind of rational explanation, an 'ultimate' explanation; if we do not have available that kind of rational

explanation, then the agent does not act with the requisite control. But this view strikes me as confused.

What an adequate libertarian account of free choice must show is how an undetermined choice can be both fully rational and under the agent's control (in a way that is more desirable than any way in which a choice may be under the control of a determined agent). The point of enquiring whether an undetermined choice could be contrastively rationally explained is to see

10 See, e.g., Nagel p. II5; Kane pp. 231-2.

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whether such a choice could be contrastively rational; and that might fairly be regarded as part of the issue of full rationality. (However, as in Edna's case, a choice may not be rationally deficient even if certain contrastive questions about it have no answer.) If the main argument of this paper is correct, then an affirmative answer to the question about full rationality is strongly supported. It does not appear that any further sort of rational explicability is required to show full rationality. Nor is it apparent that an answer to the question regarding control will undermine what I have said about rational explicability.

The degree or variety of control that an agent has over any given choice is fundamentally a matter of what does or does not causally produce (and in what manner it causally produces) that choice. I have argued here that the requirement of causal indeterminism allows for contrastive rational explicability. It might be argued (and I would agree) that the libertarian requirement for control involves more than causal indeterminism. But what more is required concerns the causal production of the choice; and not all causes either add to or subtract from otherwise available causal explanations. It may well be that the further requirement for control can be satisfied without either adding to or subtracting from rational explicability. Certainly some argument would be needed to support a claim to the contrary. Until we have such an argument, we have no warrant for dismissing as inadequate the sorts of contrastive rational explanations I have claimed to be available.

There is an additional respect in which Nagel's and Kane's treatment of explicability and control is, I think, in error. Both writers appear to believe that the further control required for free choice is implied by a combination of indeterminism and the availability of a kind of non-causal rational explanation. But if agent-control is indeed fundamentally a matter of what does and does not cause a choice, then this belief appears mistaken. The availability of some kind of non-causal explanation would seem to contribute nothing to control.

In sum, the issues of rational explicability and of agent-control do not appear to be connected in the tight way suggested by Nagel and Kane. The present paper provides, I submit, a good part of a solution to the former issue. If we want a solution to the latter, we need to turn to something other than questions about rational explicability."

University of Georgia

" For helpful comments on earlier drafts of this paper, I wish to thank Charles Cross, Robert Kane, Peter Lipton and anonymous referees for this journal. A version of this paper was presented to a colloquium at Georgia State University; I am grateful to the audience for their comments.

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