The Compatibility of Mechanism and Purpose Alvin I. Goldman The Philosophical Review, Vol. 78, No. 4. (Oct., 1969), pp. 468-482. Stable URL: http://links.jstor.org/sici?sici=0031-8108%28196910%2978%3A4%3C468%3ATCOMAP%3E2.0.CO%3B2-W The Philosophical Review is currently published by Cornell University.
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THE COMPATIBILITY OF MECHANISM
AND PURPOSE
N
ORMAN MALCOLM'S recent argument against the con-
ceivability of mechanism1 rests on the claim that purposive explanations of behavior-that is, explanations of behavior in terms of desires or intentions-are incompatible with neurophysiological explanations of behavior. Malcolm imagines a neurophysiological theory that provides "sufficient causal explanations" of human behavior. Given such a theory, he says, a man's behavior would not be explainable in terms of his desires or intentions. If, for example, the movements of a man up a ladder were explainable by reference to neurophysiological states, reference to the man's desires or intentions would be irrelevant: the movements of the man on the ladder would be coqbletely accounted for in terms of electrical, chemical, and mechanical processes in his body. This would surely imply that his desire or intention to retrieve his hat had nothing to do with his movement up the ladder. I t would imply that on this same occasion he would have moved up the ladder in exactly this way even if he had had no intention to retrieve his hat, or even no intention to climb the ladder. To mention his intention or purpose would be no explanation, nor even part of an explanation, of his movements on the ladder. Given the antecedent neurological states of his bodily system together with general laws correlating those states with the contractions of muscles and movements of limbs, he would have moved as he did regardless of his desire or intention. If every movement of his was completely accounted for by his antecedent neurophysiological states (his "programming"), then it was not true that those movements occurred because he wanted or intended to get his hat [p. 531.
Malcolm claims that the man's intentions or desires would not "The Conceivability of Mechanism," Philosophical Review,LXXVII (1968). Page numbers in parentheses refer to this paper. 468
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be causes of his movement. This is defended by an examination of the implications of causal attributions. It has often been noted that to say B causes C does not mean merely that whenever B occurs, C occurs. Causation also has subjunctive and counterfactual implications: if B were to occur, C would occur; and if B had not occurred, C would not have occurred. But the neurophysiological theory would provide sufficient causal conditions for every human movement, and so there would be no cases at all in which a certain movement would not have occurred if the person had not had this desire or intention. Since the counterfactual would be false in all cases, desires and intentions would not be causes of human movements. They would not ever be sufficient causal conditions nor would they ever be necessary causal conditions [pp. 56-57]. Let us look at the last sentence of this passage. It makes two claims: first, that desires and intentions would never be sujicient conditions for human movements, and second, that desires and intentions would never be necessary conditions of human movements. The first claim seems to me unfounded and unargued for. Malcolm himself admits that "generally speaking, it is possible for there to be a plurality of simultaneous sufficient causal conditions of an event" (p. 56). Thus, from the fact that there are neurophysiological states which are causally sufficient for a given movement, it does not follow that desires or intentions (together with beliefs and other relevant events) are not (also) causally sufficient for the same movement. It is at least conceivable that all human movements have two sets of sufficient conditions, one involving neurophysiological states and one involving desires or intentions. An argument is needed to prove that this is not, or could not be, the case. At first glance, however, Malcolm's second thesis appears to be justified, and perhaps this is all he needs for his central contention. The second thesis appears to flow from the definitions of "sufficient" and "necessary." To say that X is sufficient for Y appears to mean that nothing over a n d above X is needed for the occurrence of Y-in other words, that nothing over and above X is necessary for the occurrence of Y. Thus, if neurophysiological states are sufficient for the occurrence of certain movements, it would appear to follow that intentions or desires are not necessary
ALVIN I. GOLDMAJV
for the occurrence of these movements. If, moreover, desires or intentions could not be causes or explanatory factors of movements unless they were necessary for the movement^,^ then the fact that neurophysiological states are sufficient for the movements would imply that desires or intentions are not causes of the movements and cannot be used to explain the movements. Despite its apparent plausibility, however, I wish to challenge this alleged connection between necessary and sufficient conditions, at least in causal contexts. I admit that intentions or desires can be causes of behavior only if they are necessary for behavior, and, generally, that events can be causes only if they are necessary for their effects (except in cases of over-determination). What I wish to deny is the contention that ifneurophysiological states are suficient for behavior, then desires or intentions are not necessary for behavior. This latter contention seems to me the crux of Malcolm's argument for the incompatibility of mechanism and purpose; if this contention can be shown to be unacceptable, Malcolm's conclusion that mechanism and purpose are incompatible will remain without support.
The principle Malcolm seems to presuppose can be formulated as follows. (I) If events C,, . . . , Ch are jointly suficient for the occurrence of event E, then no events other than C,, . . . , Ch are necessary for the occurrence of E.
I use the term "event" here very broadly, broadly enough to 2 Actually, in cases of "over-determination" a cause of Y is not a necessary condition for the occurrence of Y.If George's shooting his gun (at t,) and Oscar's shooting his gun (at t,) are individually sufficient for John's dying (at tz),then each shooting is a cause of John's dying. But neither of the shooti n g ~is a necessary condition of John's dying, for if one of the shootings had not occurred, the other would have sufficed to cause John's death. Thus, it is not quite accurate to say that being a cause of Y entails being a necessary condition of Y.I shall henceforth waive this point, however, since I do not wish to suggest that behavior is over-determined in the way that John's death is overdetermined. I shall admit that in order for intentions or desires to be causes of behavior, they must be necessary for behavior.
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cover states of affairs and processes as well as what would ordinarily be called "events." I assume that every specific event occurs at a specific time. For example, events Cl, . . . , Ch may all occur contemporaneously, at t,, and their joint occurrence at t2 may be sufficient for the occurrence of E at t,. To say that Cl , . . . , Ch are jointly "sufficient" for E is to say that there are laws or regularities which, given the occurrence of Cl , . . . , Ch , ensure the occurrence of E. To say that some event is "necessary" for the occurrence of E is to say that laws and regularities ensure that, if this event had not occurred, then E would not have occurred. Despite the initial plausibility of principle (I), it can be shown to be false. Reflection on (I) reveals that it has the effect of precluding the possibility of a chain of events (or sets of simultaneous events) each link of which is a cause of a succeeding link, and each of which can be considered a cause of the final link of the chain. That there are such chains seems to me obvious; it seems then obvious that if W causes X which causes Y which causes each of the links, W, X, and T, can be considered a cause of But principle (I) precludes the possibility of such a chain. To show this, let us suppose that events Cl , . . . , Ch , all occurring at t, ,are jointly sufficient and necessary for the occurrence of E at t,. Further suppose that Cl , . . . , Ch are simply one group of events in a sequence of causes of E; that is, suppose that there are events at t1 which cause the occurrence of Cl , . . . , Ch at t2, that Cl , . . . , Ch cause the occurrence of certain events at t3, and that these events at t3 cause the occurrence of E at t, . Finally, suppose that each of these sets of events, at tl , at t2 , and at t, , can be considered a cause of the occurrence of E at t, . Now since Cl , . . . , Ch are sufficient for the occurrence of E, principle (I) implies that no events other than C, , . . . , Ch are necessary for the occurrence of E. From this it follows that no events either before or after t, are necessary for the occurrence of E. This means that the indicated events at t, or t3 are not necessary hr the occurrence of E. But if they are not necessary for the occurrence of E, then they are not a cause of E. This contradicts our original assumption-namely, that each of these groups of events is a cause of E.
z,
z.
ALVIN I. GOLDMAN
A slightly different way of seeing how chains of causes prove the unacceptability of (I) is this. Ex hykothesi, Cl , . . . , C, are a cause of E, and hence necessary for the occurrence of E. But precisely the reason we would have for saying that C, , . . . , C, are necessary for E is equally a reason for saying that, for example, the indicated events at 5 are necessary for E. We say that C,, . . . , Ch are necessary for E because if they had not occurred (at t,), then the relevant events at t3 would not have occurred; and if the events at t3 had not occurred, then E would not have occurred. But this very argument shows that the events at t3 are necessary for E, since it was explicitly stated in the argument that if these events at t3 had not occurred, then E would not have occurred. It must be admitted, therefore, that if C, , . . . , Ch are causes of E, then the events at t3 are necessary for E. Yet this contradicts principle (I). It is tempting to reply to the last argument as follows. "The events at t3 are not really necessary for the occurrence of E. As long as C, , . . . , Ch occur at t, , the occurrence of the relevant events at t3 is ensured. Hence, the occurrence of E does not really depend on the events at 5 , but only on Cl , . . . , C, ." This mode of argument is clearly unacceptable. If we accept it, it will follow that the "real" cause of an event is only an "originating" cause, never an ccintermediary"cause. If so, most if not all of the things we ordinarily call ''causes" will turn out not to be causes at all. Moreover, C, , . . . , C, will turn out not to be causes of E. For we can argue, as above, that since C,, . . . , C, must occur as long as the relevant events at t, occur, then the occurrence of E does not "really" depend on Cl , . . . , Ch , but only on the events at t,. My objection to principle (I) has rested on the fact that some events occurring at a different time from Cl, . . . , C, may be necessary for the occurrence of E even though C, , . . . , C, are sufficient for the occurrence of E. But this may be considered irrelevant to Malcolm's purposes. The neurophysiological theory envisaged by Malcolm is one which presumably describes continuous neurophysiological activity leading to the overt behavior. Thus, if desires or intentions were to cause behavior, they would not be subsequent to all relevant neurophysiological states, nor
MECHANISM AND PURPOSE
would they be prior to all relevant neurophysiological states. Rather, they would have to be simultaneous with some set of neurophysiological states that are causally sufficient for the behavior. Thus, if I am to maintain that desires or intentions would be causally necessary for the behavior, a principle weaker than (I) must be disproved. Instead of principle (I) it would adequately serve Malcolm's purposes to employ the weaker principle, (11) : (11) I f events C* occurring at tl are sujicient for the occurrence of E at t , , then no other events at tl are necessary for the occurrence of E at t,. I believe that principle (11), like principle (I), can be proved unacceptable. Suppose there is a (contingent) law saying that for any object of kind H a n d any time t, the object has property 0 at t if and only if it has property Y at t.3 Then if a particular object a has properties Q, and Y at a particular time tl , I shall say that a's having Q, at t1 is a "simultaneous nomic equivalent" of a's having Y at t, . Now suppose that particular events (or sets of events) C* and C** are simultaneous nomic equivalents. This means that C* is sufficient for C** and that C** is sufficient for C*; equivalently, it means that C* is necessary for C** and that C** is necessary for C*.4 Further, suppose that C* is suficient for the occurrence of a subsequent event E (at t,) and necessary for the occurrence of E. Then there is another event (or set of events)namely, C**-that is simultaneous with C* and is also necessary for the occurrence of E. This follows directly from the transitivity of the relation, "A is necessary for B." Since C* and C** are simultaneous nomic equivalents, C** is necessary for C*. But ex hypothesi C* is necessary for the occurrence of E. Hence, C** is also necessary for the occurrence of E. If C* had not occurred (at This point is suggested by Richard Brandt's and Jaegwon Kim's principle of "simultaneous isomorphism," in "The Logic of the Identity Theory," Journal of Philosothy, 64 (1967). * Each event is sufficient for the other, but perhaps neither is causally sufficient for the other. It may be inappropriate to speak of a causal relationship holding between such a pair of events, first, because they are simultaneous, and second, because causal relationships must be unidirectional, and there may be no grounds for deciding the directionality of the causation in such cases.
ALVIN I. GOLDMAJV
t,), then E would not have occurred (at t,); but similarly, if C** had not occurred (at t,), then E would not have occurred (at t,). (By a similar argument, C** is seen to be sufficient for E as well.) We have a case, then, in which principle (11) is violated; for here is an event (causally) sufficient for E that is accompanied by a different but simultaneous event that is necessary for E. Notice that the grounds for saying that C** is necessary for E are precisely those presupposed in saying that C* is necessary for E. C* is said to be necessary for E because, given the laws of nature, the omission of C* (at t,) would have meant that the events at t, would not be sufficient for the occurrence of E. Similarly, given the laws of nature, the omission of C** (at t,) would have meant that the events a t t, would not be sufficient for the occurrence of E. Given the laws of nature, the omission of C** (at t,) would have necessitated the omission of C* (at t,). And the omission of C*, we have seen, would have resulted in the nonoccurrence of E.
The possibility of simultaneous nomic equivalents shows the unacceptability of principle (11). But how does this apply to the compatibility of neurophysiological causation and purposive causation? Could intentions or desires be simultaneous nomic equivalents with neurophysiological states? I see no reason why this could not be true. It is certainly logically possible, and probably compatible with present information, that there should be laws saying that for any human being (or organism of a certain sort), and for any time, the human being will have a specific intention at that time if and only if he is in a specific neurophysiological state at that time. Thus, suppose that John's being in neurophysiological state N a t time t, is a simultaneous nomic equivalent of John's intending to retrieve his hat at time t,. Then any movement or behavior for which John's being in state N is a necessary condition is also a movement or bit of behavior for which John's intending to retrieve his hat is a necessary condition. Similarly, any movement or bit of behavior for which John's being in state N is a sufficient condition is also a movement or bit of behavior
MECHANISM AND PURPOSE
for which John's intending to retrieve his hat is a sufficient condition. Thus, John's intending to retrieve his hat might have the same causal status as John's being in state JV vis-d-vis any movement of his. How would this possible view of the relation between intentions and neurophysiological states compare with traditional views about the mind-body relationship, such as epiphenomenalism, parallelism, and interactionism? First, it would not commit one to epiphenomenalism, which posits a one-way causal relationship between physical events and mental events. Because of the simultaneity of the mental and physical events, we probably could not speak of a causal relationship between them. But if there is a causal relationship--or if we choose to call it a "causal" relationship-it is not obvious why we should say that the neurophysiological state causes the intention rather than vice versa. Thus, epiphenomenalism would be ruled out by the simultaneous nomic equivalents position, or at least would not be entailed by it. Of course, the denial that simultaneous nomic equivalents are causally related does not imply that they merely "parallel" each otherthat is, that their co-occurrence is purely accidental. The view that the correlation between mental states and bodily states is merely accidental is part of the traditional doctrine of parallelism. But since a universal law is involved in nomic equivalents, this position would have to be rejected. Finally, how would the proposed position compare with interactionism, the view that mental events are sometimes caused by bodily events and that bodily events are sometimes caused by mental events? On the one hand, we are not committed to the view that simultaneous nomic equivalents themselves are causally interrelated. So if this is implied by interactionism, the present hypothesis can be distinguished from interactionism. On the other hand, the present view does suggest causal relationships between neurophysiological events and subsequent mental events and between mental events and subsequent neurophysiological events. Suppose that a's being in state JV and a's having intention I are simultaneous nomic equivalents, both occurring at t, . Further, suppose that a's being in state JV' and a's having intention I' are also simultaneous nomic equivalents, both occurring at t, . Finally,
ALVIN I. GOLDMAN
suppose that there is a causal relationship between the pair of nomic equivalents at tl and the pair of nomic equivalents at t, . Then both a's being in N a n d a's having I are causes of a's being in N', and both a's being in N and a's having I are causes of a's having I'. Thus, we have at least one physical event being the cause of at least one mental event, and at least one mental event being the cause of at least one physical event. This is illustrated in the diagram below, in which arrows represent causal relationships and dashed lines represent nomic, noncausal relationships.
My suggestions could be made more perspicuous by an example of simultaneous nomic equivalents outside the arena of the mindbody relationship. Unfortunately, it is difficult to find examples that are perfectly analogous to the mental event/physical event picture I have sketched. I shall present an example to help illustrate the view, but I am not wholly satisfied with it. Every real (as opposed to ideal) gas has a schedule which associates a temperature with a vapor pressure point. A vapor pressure point is the amount of pressure just sufficient to cause condensation of the gas. As the temperature of the gas increases, there is a corresponding increase in the amount of pressure required for condensation (although above a certain temperature, no amount of pressure will cause condensation). Thus, there are laws like the following: for any body of gas of kind G, and any time t, such a body will have temperature T a t t if and only if it has vapor pressure point V'at t. Now suppose there is a particular body of gas g, of kind G, which has temperature T a t tl and vapor pressure point V at tl . Then g's having T at tl is a simultaneous nomic equivalent of g's having Vat tl . Notice that g's having T at tl and g's having V at tl are fairly clearly distinct states of affairs, and notice too that it is not very plausible to say that g's
MECHANISM AND PURPOSE
having T at tl is a "cause" of g's having V at tl , or vice versa.5 Now suppose that we have this body of gas g under constant pressure P. At tl g has temperature T and vapor pressure point V, where V is greater than P. By reducing the temperature ofg, however, we reduce the vapor pressure point of g, and when the latter is reduced as low as P, condensation results. Now consider the change in temperature of g and the change in vapor pressure point of g. In other words, consider g's undergoing a certain loss in temperature (between tl and t,) and g's undergoing a (corresponding) reduction in vapor pressure point (between tl and t,). This pair of events, like the pair of states above, are simultaneous nomic equivalents. Moreover, each of them is the cause (or a cause) of the condensation of g. Given the fact that g is under pressure P, g's undergoing a certain loss in temperature (between tl and 8,) is causally sufficient for the condensation; but equally, g's undergoing a certain reduction in vapor pressure point (between tl and t,) is causally sufficient for the condensation. Again, each of these events is a causally necessary condition (in the circumstances) of the condensation. If g had not undergone the change in temperature, the condensation would not have occurred; and if g had not undergone a change in vapor pressure point, the condensation would not have occurred. (Since, in the present case, the change in temperature would have to be effected by a reduction of the volume, that change in volume could also be considered a cause of the condensation. Thus, there would be three simultaneous causes of condensation. 'j) 6 I am indebted to Mack F. Harrell for the example. One slight disanalogy between this example and the psychophysical case is that vapor pressure point is a purely dispositional concept. I would not want to view the concepts of intention and desire as purely dispositional concepts; probably Putnam's and Fodor's view of psychological states as "functional states" comes closer to the truth. Cf. Hilary Putnam, "Psychological Predicates," in W. H. Capitan and D. D. Merrill (eds.), Art, Mind, and Religion (Pittsburgh, 1967); and J. A. Fodor, "Explanations in Psychology," in Max Black (ed.), Philosobhy in America (London, I 965). 6 A second problem with this example is that we are tempted to say that the change in vapor pressure point is dependent on the change in temperature, but not vice versa. This is probably because we can sometimes directly vary the temperature, while the vapor pressure point cannot be varied except via the
ALVIN I. GOLDMAN
Many philosophers would argue, of course, that John's being in state N and John's having intention I are identical events or states of affairs. This is a possibility I would not rule out, though I am not defending it here. But Malcolm cannot espouse this identity, since it would vitiate the entire argument for the incompatibility of purposive causation and neurophysiological causation. What I have been trying to show is that the identity theory is not the only way of defending the compatibility thesis. There are, I believe, at least two ways7 to defend the compatibility of neurophysiological and purposive causation (or explanation) : first, by the identity theory, and second, by the hypothesis of simultaneous non~icequivalents. Malcolm argues against the first alternative in his article, but he presents no arguments against the second alternative.
Let me try to anticipate two possible objections to my argument. First, it might be objected that although I have shown the possibility of desires or intentions being necessary for behavior, I have not shown the possibility of their being causal& necessary for behavior. If intentions were causally related to neurophysiological states, then perhaps intentions could be said to be causally related to behavior. But my position explicitly suggests that intentions and neurophysiological states are not causally related, although temperature. The case of intentions is slightly different. Although we could affect intentions by chemically changing the person's neurophysiological states, we could also affect his intentions by arguing with him, urging him, etc. In the latter case, I should not want to say that we were only "indirectly" changing his intention, via his neurophysiological state. 7 There may be further hypotheses that also allow for the compatibility of the two kinds of causation and explanation. For example, there may turn out to be no species-wide law that provides a one-one correlation between mental states and neural states. The pattern of correlation might be different for each distinct organism. This would not allow mental and physical states to be called simultaneous nomic equivalents, at least not in the narrow way I have defined this notion. Nevertheless, although the relationship between the states would be "weaker," the compatibility argument might still hold good. I am indebted to the editors of the Philosofihical Reuiew for indicating this point to me.
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they are nomically related. Hence, runs the objection, what is the justification for saying that intentions are causalb related to behavior ? My first comment on this objection is to note that Malcolm himself thinks that desires and intentions (at least some intentions) are causes of behavior. He bases this on the fact that desires and intentions can be used both to explain and to predict behavior:
I shall use the word "causeJ' in its widest sense, according to which anything that explains, or partly explains, the occurrence of some behavior is the cause, or part of the cause, of the behavior [p. 591. It is a natural use of language to ask, "What caused you to climb the ladder?"; and it is an appropriate answer to say, "I wanted to get my hat" [p. 601. If dispositions are causes, we can hardly deny the same role to intentions. Both are useful in predicting behavior. If I am trying to estimate the likelihood that this man is going to do so-and-so, the information that he has a disposition to do it . . . will be an affirmative consideration. I am entitled to give equal or possibly greater weight to the information that he intends to do it. Not only do simple intentions have weight in predicting actions, but also they figure in the explanation of actions that have already occurred. If a man who has just been released from prison promptly climbs a flagpole, I may want an explanation of that occurrence. If I learn that he had previously made up his mind to do it, but had been prevented by his imprisonment, I have received a partial explanation of why he is climbing the flagpole [pp. 60-611. Obviously, Malcolm thinks that desires and intentions can a t least sometimes be considered causes of behavior. The only reason he offers to think otherwise, indeed, is the possibility of neurophysiological causes. The presence of neurophysiological causes, he contends, would erase the effect of intentions because intentions would then not be necessary for the behavior. Once we have seen, however, that Malcolm is mistaken in saying that the intentions would then not be necessary for behavior, why should we not return to Malcolm's own view that the intentions are causes of behavior? Prior to the argument concerning necessary and sufficient conditions, there is every reason to think that desires and intentions cause behavior. Once we see that that argument does
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not go through as Malcolm believes it does, we have no reason to deny that desires and intentions (sometimes) cause behavior. Indeed, if intentions were simultaneous nomic equivalents of neurophysiological states, they could still be invoked both to explain and to predict behavior. The fact that John desired or intended to retrieve his hat would serve as an explanation, or at least a partial explanation, of his climbing the ladder. And the fact that he desired to retrieve his hat, and believed that he could do this by climbing the ladder, would justify our predicting that he would climb the ladder. Thus, since explanation and prediction are invoked by Malcolm himself in assigning causes, we would have every reason to consider intentions to be causes of behavior even if they were simultaneous nomic equivalents of neurophysiological states. Finally, it is not a (logically) necessav condition of intentions' being causally related to behavior that they be causally related to neurophysiological states. Admittedly, if intentions caused neurophysiological states which in turn caused behavior, then it would follow that intentions caused the behavior. But this is not the only circumstance in which we might be justified in saying that intentions caused behavior. In particular, it seems quite plausible to say that pairs of simultaneous nomic equivalents often are causes of the same effects, even though the simultaneous nomic equivalents are not themselves causes of one another. I a m not convinced of the principle that two simultaneous nomic equivalents must both be causes of a y effect of which one is a cause. But it certainly seems likely that there are some effects which are caused by both of two simultaneous nomic equivalents. The second objection to my position that I wish to anticipate is the contention that my position implies a sort of universal overdetermination of human behavior. If two people simultaneously shoot John, then John's death is over-determined. But such cases are comparatively rare, and it would be remarkable that all events of a certain generic kind should be over-determined in this way. Yet, it might be objected, this is what my proposal of simultaneous nomic equivalents seems to envisage. I t seems to suggest that every case of human behavior is over-determined in the way that John's
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death is over-determined. And this-so goes the objection-is extremely implausible. My reply is that the status of simultaneous nomic equivalents is significantly different from the status of two distinct shootings. The most obvious difference is that the shootings involve distinct, spatially removed entities (the two agents and the two guns), while the nomic equivalents are events involving the same entity (the agent). Secondly, the two shootings are independent in the sense that neither is necessary or sufficient for the other, while the nomic equivalents are both necessary and sufficient for their opposite numbers. Or, if there is a relationship of necessity or sufficiency holding between the two shootings, it will be a causal relationship, while the nomic equivalents are not related causally. Despite these differences, of course, we are a t liberty to call causation by simultaneous nomic equivalents cases of "over-determination"; this is purely a terminological matter. But if so, we should not be misled into thinking that these cases are just like the shooting case. Nor should we find it remarkable or unbelievable that all human behavior should be caused both by intentions and by neurophysiological states. One final comment on Malcolmysattempt to show the incompatibility of mechanism and purpose. He frequently writes that the envisaged neurophysiological theory is "comprehensive" or c complete." He says, for example, that 6
the postulated neurophysiological theory is comprehensive. It is assumed to provide complete causal explanations for all bodily movements that are not produced by external physical forces. It is a closed system in the sense that it does not admit, as antecedent conditions, anything other than neurophysiological states and processes. Desires and intentions have no place in it [p. 561. There are two crucial ambiguities concealed in this passage. The first concerns the terms cccomplete" or "comprehensive." To say that the neurophysiological theory is crcomplete" may mean ( A ) that all human behavior not caused by external forces can be explained by neurophysiological states, or (B) that human behavior not caused by external forces can be explained only by neurophysiological states. The second ambiguity concerns the claim that the theory "does not admit" anything other than neuro-
ALVIjV I. GOLDMAN
physiological states and processes. This may mean ( A ) that the theory fails to include reference to other factors, such as psychological states, or ( B ) that the theory excludes the use of other factors, such as desires or intentions, in explanations of behavior. In each case, conclusion ( A ) is clearly justified. But Malcolm thinks that in each case conclusion (B) is justified as well. And this, I believe, is where he goes wrong. Scientific theories normally specify events that do or can lead to certain other events, not what events do not or cannot lead to other events. The envisaged neurophysiological theory says things like, "Whenever an organism of structure S is in neurophysiological state q it will emit movement m." If we observe an organism 0 of structure S emitting movement m and if we ascertain that 0 was in state q prior to emitting m, we may infer that 0's being in state q caused 0's emitting m. If, moreover, we never discover any emission of movement m by an organism of structure S that is not preceded by its being in neurophysiological state q (except for cases where there are external physical forces), then we may conclude that the theory is "complete" in the sense of accounting for all movements of kind m in neurophysiological terms. But the evidence cited thus far does not justify the inference that emissions of movement m by organisms of structure S are not caused by psychological states as well-say, desires or intentions. The theory at hand and the evidence available is simply silent on the matter, for they tell us nothing whatever about psychological states. I do not wish to deny that we can conceive of empirical information that would justify the conclusion that movements of kind m are never caused by intentions; though the required information would probably have to justify the conclusion that there are no intentions. The important point, however, is that it is not at all obvious that the evidence required to deny the role of intentions is the same evidence that justifies the conclusion that certain neurophysiological states lead to certain kinds of movements. The precise nature of the relevant bodies of evidence should be a subject for future study. ALVIN I. GOLDMAN
University of Michigan
