Explanation and Diagnosis in Economics Daniel M. Hausman London School of Economics and University of Wisconsin-MadisonPublished in Revue Internationale De Philosophie 55 (2001): 311-26.Economists disagree about whether they should aim to provide explanations, about what theyshould aim to explain, and about how they should go about explaining. This essay will addressall three of these controversies. I shall argue (1) that explanation is a central task in economics,(2) that one should adopt an explicitly causal model of explanation, (3) that economists cannotavoid explaining individual choices and they should attempt to explain the paths that take theeconomy from one equilibrium to another, and (4) that explanations in economics cite reasons aswell as causes. Most of these points apply across different schools of economics, but“economics” in this paper should thus be read as “mainstream economics.”1 Should explanation be a goal?Milton Friedman asserts famously that the goal of economics, like that of all of science, “is thedevelopment of a “theory” or “hypothesis” that yields valid and meaningful (i.e., not truistic)predictions about phenomena not yet observed“ (1953, p. 7). He does not argue explicitly thateconomists should not aim to give explanations. Indeed he never even mentions such a view. Hedismisses explanation as a goal by asserting that the goal of science is exclusively predictive andby scare quotes around many of his uses of the word, “explain.”Economics is obviously largely oriented toward its possible contributions toward policy, andFriedman’s view that its goals are exclusively predictive has struck a responsive chord. ButFriedman forgets to put scare quotes around all of his uses of the word, “explain,” and he neverclariﬁes what the word means with or without its ornaments. He writes, for example, Yet, in the absence of other evidence, the success of the hypothesis for one purpose—in explaining one class of phenomena—will give us greater conﬁdence than we would otherwise have that it may succeed for another purpose—in explaining another class of phenomena. (1953, p. 28)Here Friedman speaks of explaining phenomena or classes of phenomena as a “purpose.” He hasalready insisted that the purpose of economics is the development of theories that provide validand meaningful predictions. Is there an inconsistency here?One way to make sense of Friedman’s text is to take explanation to be just like prediction exceptthat the phenomenon to be explained has already been observed. Prediction, not explanation,remains the ultimate goal. But explanation in this sense may be a proximate goal, since atheory’s success at explanation is evidence that it will succeed in prediction.This line of thought provides a reason for those who hold a narrow anti-realist view of science tobe concerned about “explanation” in only a minimalist sense. What scientists and lay people callexplanations are not just derivations from theories of what is known. In equilibrium the wage andthe value of the marginal productivity of labor are mutually determined and equal. But the wagedoes not explain the marginal productivity, nor does the marginal productivity explain the wage.
2Neither does one explain the height of a ﬂagpole by deducing it from the length of its shadowand the angle of elevation of the sun. Explanations of events or states of a affairs cite causes.Should economists be concerned about explanation in this richer, causal sense?Consider a contemporary example. There is considerable interest among economists inexplaining why there has been a stark increase in inequality within the United States. Both thethe Summer 1995 and the Spring 1997 issues of the Journal of Economic Perspectives featuredsymposia on this question. Words such as “explains” “accounts for” and “causes” are usedrepeatedly in these essays. Some of these uses seem compatible with a minimalist view ofexplanation as prediction of what is already known. For example, Peter Gottschalk writes,“Figure 6 shows a very rapid increase in the experience premium for males during the early1970s, which partially explains why overall inequality could increase in the early 1970s in spiteof the decline in the education premium for males during this early period” (1997, p. 31). Butdespite the use of the word, “explains” here, Gottschalk does not regard this observation asexplanation. He describes his essay as “bring[ing] together the factual material on changes in thedistribution of labor market income, which any of these theories must address” (1997, p. 23).Knowing that more experienced male workers were paid relatively more may help explain theoverall increase in inequality or it may be symptomatic of factors that independently led to anincrease in overall inequality. Merely identifying a correlation that could have been used topredict an overall increase in inequality does not explain why there has been such an overallincrease.Why should we have an institution that aims (according to Friedman) to develop theories thatprovide valid and meaningful predictions about phenomena not yet observed? Friedman’sanswer is evident. We’re interested in controlling economic events, not just passively watchingthem. We want to be able “to predict the consequences of changes in circumstances” (1953, p.39). Economists and policy makers face speciﬁc problems, such as “to determine the effect onretail prices of cigarettes of an increase, expected to be permanent, in the federal cigarette tax”(1953, pp. 36-37). For this practical purpose a model that treats cigarette ﬁrms “as if they wereproducing an identical product and were in perfect competition” (1953, p. 37) will provide theneeded predictions. If the problem is instead to predict how cigarette ﬁrms would react to pricecontrols in World War II, a different model should be used. Friedman is not increased inprediction for its own sake. He wants prediction in order to guide policies. He wants economictheories to provide predictions that are useful for practical purposes.Although he does not say so in so many words, Friedman thus wants economic theory todetermine the causes of phenomena. We want to be able “to predict the consequences ofchanges in circumstances” “to determine the effect on retail prices” of a tax increase. Discoveringa correlation between two things that are not related as cause and effect, though not useless, isless helpful. Knowing that falling barometer readings are correlated with storms tells us when totake shelter. But the usefulness of such a correlation between effects of a common cause islimited. It does not tell us how to do anything about storms. Identifying causes is of much morepractical importance. When we know the causes, we are not only warned about what willhappen. We may also be able to act to bring things about or to prevent them. If we cannotmanipulate the causes (as in the case of storms), then we cannot manipulate the effects, but eventhen it is better to know the causes than merely to know correlations; for at least we know whatlevers to pull if only we had the strength to pull them.Friedman’s no-nonsense practical “instrumentalist” orientation, which he takes to lead awayfrom a concern with explanation, actually leads toward an interest in explanation. For one kindof explanation is the discovery of causes, and knowledge of causes is exactly what is needed forpractical purposes. One one looks at the debate concerning the explanation of the growth ofincome inequalities, one ﬁnds that the participants are explicitly concerned about causes. Forexample, J. David Richardson concludes that “it may be difﬁcult to sparate trade from
3technology as a cause of growing income inequality,” (1995, p. 51). Similarly, George Johnsonargues that the experience and education premia are explained by a shift in demand for high-skilled labor and that shift in demand in turn has two main causes (1997, p. 46) — the increasedopenness of the U.S. economy and skill-biased technological changes.As this example (to which I will return in section 3 below) illustrates, economists sometimesdebate long and hard about the causes of a phenomenon. Such a debate is, obviously, a debateabout the explanation of the phenomenon, because to cite the causes of some aspect of an eventor state of affairs is to explain it. Someone who defends Friedman’s view that the goals ofeconomics are exclusively predictive might, of course, regard debates like those devoted todetermining the explanation of the large increases in inequality in the U.S. and the U.K. asconfused wastes of time and energy nurtured by methodological mistake. But they might alsotake a more compromising (and much more plausible line). If the ultimate goal of economics isuseful prediction, and useful prediction requires knowledge of causes — that is, diagnosis —,then explanation is a central task. It is a central task, because the practical objectives ofeconomists require that they explain phenomena, whether or not they should (as I believe) alsoaim disinterestedly at pure knowledge or the resolution of curiosity.The question of whether economists should be concerned to explain phenomena or only topredict it is to some extent independent of questions about the ultimate goals of economics or ofscience in general. Whether those goals are the disinterested pursuit of pure knowledge or thepractical pursuit of useful predictions, economists need to seek out the causes of things.Diagnoses assist in cures. Only an anti-realist who also plays down the practical goals of sciencecan repudiate the search for causes.2 How economists explainIn contemporary work in philosophy of science, one ﬁnds three main accounts of scientiﬁcexplanation.1 First, there is the old-fashioned deductive-nomological model (Hempel 1965). Toexplain is to deduce a statement of what is to be explained from a set of true statements includingessentially at least one law of nature. If one were to take this as necessary and sufﬁcient forscientiﬁc explanation, then one would have something like the “explanation as prediction of whatis already known” view discussed above. Unlike that view, however, the deductive-nomologicalmodel insists that the statements in the explanans all be true. But nobody believes that theconditions of the deductive-nomological model are sufﬁcient for scientiﬁc explanation. One candeduce that a man who takes birth-control pills regularly will not get pregnant from the law thattaking birth-control pills prevents pregnancy, but one has surely not explained why the man doesnot get pregnant (Salmon 1971, p. 34). The conditions of the deductive-nomological model arenot necessary either, because they rule out probabilistic explanation. It certainly seems that onecan explain events that are not determined. So the deductive-nomological model is (to put itmildly) problematic.A second account of explanation is pragmatic.2 Explanations are responses to why questions.To understand what explanations are requires attention to the nature of why questions. What dosuch questions presuppose? What sort of information are people looking for when they askthem? When people ask, “Why have income inequalities in the United States increased?” theypresuppose that they are correct about the “topic” — that inequalities have indeed increased. Ifthey are wrong about that, one responds by criticizing the why question rather than answering it.———————1. This is (unsurprisingly) a simpliﬁcation. I am passing over many views of explanation.2. See Achinstein 1971; van Fraassen 1980, and Miller 1987. This paragraph follows van Fraassen’s version (1980, ch. 5).
4Second, one needs to recognize the “contrast class” that is implicit in the question. People wantto know why income inequality has grown so much, not why it has not grown more. In somecontexts they may want to know why it has grown in the U.S. rather than in Norway; in othersthey may want to know why it grew in the U.S. in the 1970’s and 1980’s rather than in the 1940sand 1950s. An answer to a why question must discriminate the topic from the alternatives in theimplicit contrast class. A purported explanation for the increased inequality that implies thatinequality should have increased just as much in Norway or in the 1940s and 1950s fails toanswer the question. The answer must also be “relevant.” There may be a good correlation inthe U.S. between inequality and percentage of recreational trucks in use, but the percentage ofrecreational trucks in use fails (in van Fraassen’s terms) to satisfy the contextually determinedrelevance relation.In simpler terminology, which van Fraassen avoids because of philosophical scruples concerningthe notion of causation, “because the percentage of recreational trucks in use increased” does notanswer the question “Why did inequality in the U.S. increase?” because the percentage ofrecreational trucks in use is not a cause (or not a signiﬁcant cause) of the increased inequality.The third account of explanation focuses on causation. Why questions in most contexts arerequests for the causes of what is to be explained. “[T]o explain an event is to provide someinformation about its causal history” (Lewis 1986, p. 217). According to James Woodward, toexplain requires that one displays a pattern of conterfactual dependence. Such views ofexplanation are compatible with a pragmatic view, but more speciﬁc. Instead of saying that ananswer to a why question must be relevant, where relevance is determined by context, one sayswhat the relevance is: when one asks why an event occurs, one expects the answer to provideinformation about its causes. The view of explanation as citing causes or as providinginformation about causes complements the deductive-nomological model as much as it competeswith it. When one deduces price and quantity from supply and demand curves, onesimultaneously cites factors that inﬂuence price and quantity.A causal theory of explanation leaves many questions unanswered: why should citing causesexplain, while citing effects fails to explain? Why are why-questions requests for informationabout causes and not for information about effects? Although I cannot go deeply into thesequestions here (for more on them, see Hausman 1998, ch. 8), I shall argue in the next section thatthe link between explanation and diagnosis—between curiosity and the desire to cure—is crucialto their answer. To understand why explanation is so important to economics, one needs tounderstand its causal structure.33 The New Symmetry ThesisWhy does citing causes explain? When does citing causes fail to explain? Just what is thestructure of explanation in economics, and how can one make sense of that structure? The key toanswering these questions is, I think, a new “symmetry thesis.” In developing his deductive-nomological model of explanation, Hempel argued for a symmetry between explanation andprediction. If one is able to explain P, then one could also have predicted P if one had known theexplanans before knowing P. A great deal of ink was spilled over this symmetry thesis in the1950’s and 1960’s, and an appreciation of its failures helped philosophers to appreciate theinadequacies of the deductive-nomological model.———————3. Many economists have expressed discomfort with causal language because they mistakenly take it to be opposed to the insight that the values of economic variables are often simultaneously determined or because they mistakenly take causal language to commit one to the view that outcomes have a single cause. For a further defense of the claim that explanations in economics are causal, see Hausman 1983 and 1990.
5Although I would not attempt to resurrect or defend Hempel’s symmetry thesis, I think thatsomething analogous can be defended: In explaining P, one provides the knowledge concerningP needed to bring about P or to prevent P. The knowledge concerning P needed to bring about Por to prevent P may not sufﬁce actually to accomplish either of these things because actionrequires more than such knowledge. For example, Newton’s theory gives us the knowledgeconcerning tides needed to change them — just move the moon or change its mass — but ourcausal capacities are of course not yet up to the task of doing these things. There is, I suggest, asymmetry between what one needs to know for the purposes of explanation and what one needsto know for the purposes of control. Furthermore, if one supposes that the search for explanationis prompted by interests in control, this symmetry helps one to account for some of thepeculiarities of explanation.First, as already suggested, to explain requires that one cite a cause, not merely a factor thatstands in some sort of necessary or nomological relation to what is to be explained. Citing aneffect or another effect of a common cause does not explain P. Why not? Why when we askwhy do we seek information about causes? I suggest that the answer is practical. Onlyknowledge of causes is relevant to control. If one wants knowledge about how to bring about orto prevent P, knowing effects of P or other effects of causes of P will not sufﬁce. For example,Richard Freeman (following Alan Deardorff and Dalia Hakura (1994, p. 78)) points out thatsince wages and the volume of trade are simultaneously determined, “the effect of trade onwages cannot be meaningfully explored without additional speciﬁcation of what outside forcecaused trade to change” (1995, p. 27). The fact that there is a necessary connection betweenwages and volume of trade does not itself permit one to cite either to explain the other. Oneneeds to know whether the volume of trade is a cause of wages, an effect of wages, or whetherthe two are related merely as effects of a common cause. Without knowing what caused trade tochange, what assurance could we have that interventions with respect to trade would have thedesired impact on wages? Similarly, Robert Topel writes that “technical change favoring high-skill workers has been an ongoing force toward rising inequality in developed economies…”(1997, p. 61). In identifying a causal force, Topel picks out a factor that could in principle beused to inﬂuence the course of effects.Second, to explain requires more than merely citing a cause. The cause one cites mustdiscriminate between the topic and the contrast class. Consider the joke: Why was GeorgeWashington buried on a hillside? Answer: because he was dead. His being dead is, of course, acause of his being buried on a hillside, but it does not make his being buried on a hillside anymore likely than any of the other ways he might be buried. By the same token, it does notprovide the knowledge one needs to bring about or to prevent his being buried at one locationrather than another.The participants in the debate on income inequalities are well aware of this point. For example,Nicole Fortin and Thomas Lemieux argue that demand changes cannot explain why inequalityhas risen so much more rapidly in the U.S. than in any other country except the U.K., becausethere were comparable demand changes in countries in which inequalities did not growappreciably (1997, p. 76). Since comparable demand changes have often left income inequalityunaffected, there is no reason to believe that interventions in demand would reverse or acceleratethat growth. Thus one needs also to consider the role of institutional factors. Citing unchangedinstitutional structures leads to similar problems because “An existing institutional structurecannot explain by itself the growth in wage inequality in a particular country. However,institutional changes [such as a diminishing minimum wage or deunionization] can become asource of rising inequality” (1997, p. 76). An unchanged institutional structure cannot explain achanged economic reality and does not provide the knowledge need to change economic realityor to prevent its being changed.
6Third, explanations that identify causes that discriminate between the topic and the contrast classmay nevertheless be unsatisfactory, because they are too shallow. For example, even if the shiftin demand for skilled and experienced labor is a signiﬁcant and discriminating cause of theincreased inequality, one might object that “the jury is still out on what exactly is the drivingforce behind these demand changes” (Fortin and Lemieux 1997, p. 76). Such superﬁciality is asimportant from the perspective of control as from the perspective of explanation. Anintervention with respect to a causal intermediary may not be well deﬁned without knowledge ofthe underlying causes. Without knowing “the driving force behind these demand changes,” whatsense can one make of a possible intervention to inﬂuence these demand changes? Similarly,Fortin and Lemieux note that even if institutional changes are genuine and discriminating causes,they “may simply be endogenous responses to more fundamental changes in supply and demandconditions” (1997, p. 77). In that case attempting to control the growth of income inequality byreversing these institutional changes may be as fruitless as attempting to prevent World War I bypreventing the assassination of Archduke Ferdinand. The relationship between the assassinationand the war is not robust or invariant to interventions that prevent the assassination. In bothcases there might be alternative intermediaries waiting in the wings to carry the underlyingcauses to their ultimate consequences. Adrian Wood writes, “That these reductions in tradebarriers have occurred seems beyond dispute. More open to argument is whether they were themain cause of the growth of manufactured exports from developing countries, and whether theywere truly exogenous — [causally] independent, in particular, of other demand and supply shiftsin developed-country labor markets” (1997, pp. 61-2). These remarks could be read as aquestion about whether the reduction in trade barriers is genuinely a cause or whether, even if itis a cause, it is the sort of cause that is, in principle, usable for the purposes of manipulating itseffect.Explanation and diagnosis go hand in hand, even though explanation is largely driven by purecuriosity while diagnosis is largely a practical search for the sites where intervention might bepossible. The two go so far together because (I conjecture) explanation is to a considerable extenta practical matter, too. Though many scientists have had no interest in building a bettermousetrap, their curiosity and our curiosity is human curiosity; and human beings areunavoidably agents. What we want to ﬁnd out (I suggest) is the sort of information that could beuseful to agents.4 What should economists explain?I conclude that whether pursuing pure or merely useful knowledge, economists need to search forcauses and thus to explain phenomena. But which phenomena? From a “pure” perspective,research priorities depend on curiosity, theoretical tractability and theoretical centrality. Apragmatic perspective that emphasizes the practical goals of science maintains that economistsshould explain those phenomena that are of the most practical importance. The devastatingincrease in inequality in the U.S. and the U.K. is obviously of great importance, but it is notobviously of more importance than highly esoteric matters that have wide-ranging indirectconsequences.Let us bring this question of what to explain down to earth by considering two detailed andcontroversial questions. First, should economists aim to explain the choices of individuals, ordoes it sufﬁce to explain the aggregate consequences of those choices (and of many otherfactors)? Second, should economists settle, as they have, for explaining features of equilibria, orshould they also explain how economies get from the neighborhood of one equilibrium to theneighborhood of another?
74.1 Should Economists Explain Individual Choices?Economists are for the most part not interested in explaining individual choices. They are, infact, concerned to distance themselves from psychological theories. In Lionel Robbins’ words,“the implications of choice in a world of scarcity” — with which economics is concerned — “arein fact as little dependent on the truth of fashionable psychology as the multiplication table”(1935, p. 92). According to Debra Satz and John Ferejohn “rational-choice theory need not reston either psychological or individualist foundations” (1994, p. 86). On an “externalist”perspective, rational-choice theory (including microeconomics) can “explain action merely byappeal to coherence restrictions on choice” (1994, p. 86). For example, the response of ﬁrms to achange in an input price is ﬁxed by the pressures of a competitive market and has nothing to dowith the psychology of decision-makers within the ﬁrms (1994, pp. 78-79). In a similar vein,John Hicks writes, “But economics is not, in the end, much interested in the behaviour of singleindividuals. Its concern is with the behaviour of groups. A study of individual demand is only ameans to the study of market demand” (1946, p. 34).Hicks is right to observe that economists “are not much interested in the behaviour of singleindividuals.” But they may have to explain that behavior in order to explain the behavior ofgroups. To say that the study of individual demand “is only a means to the study of marketdemand” could mean that the study of individual demand is only a pedagogical step, a ladder thatcan be discarded once one ascends to the group level; or it could mean that the theory ofindividual demand is an unavoidable part of the theory of market demand. The latter seems to beHicks’ view—with one caveat—that the “falsiﬁcations” in the theory of individual demand, suchas the assumption that commodities are inﬁnitely divisible, “can be trusted to disappear when theindividual demands are aggregated” (1946, p.11n). Since individual choices are crucial links inthe causal chain leading from shocks (such as the imposition of a new tax) to some newequilibrium, explanations of individual choices, however intrinsically uninteresting they may beto economists, cannot be avoided.The most systematic defense of the view that economics can completely dispense with anyexplanation of individual choice is that provided by Satz and Ferejohn.4 Their central argumentfor “externalism” [that claims about psychology play no role in rational choice explanations]rests on the possibility that in certain environments different sets of preferences and beliefs resultin the same outcome. Since it does not matter which preferences and beliefs one imputes toindividuals, one might as well impute to them a particularly simple psychology, regardless of thecorrectness of that imputation. In this way one can explain the aggregate outcome withoutproviding any acceptable explanation of the individual choice. What matters is a particularstructure in which the actions are embedded. The preferences and beliefs are imputed from ordetermined by the structure. The structure, not the psychology, is what is doing the explaining(1994, pp. 80-81).Satz and Ferejohn are right to maintain that the structure within which rational choices areembedded, rather than the preferences and beliefs, is usually what is doing the explaining. Sincemany of the outcomes are robust over a reasonably wide variety of speciﬁcations of beliefs andpreferences, citing beliefs and preferences contributes little to explanations. But Satz andFerejohn are wrong defend “externalism” and to deny that citing beliefs and preferences has anyrole. Shallow and uninteresting causes are nevertheless causes. Furthermore, outcomes are oftendependent on speciﬁc beliefs and preferences, and the explanation of individual choices is not———————4. Despite the quotation above, Robbins concedes that economics does rest on psychology, albeit on utterly uncontroversial psychology. For a more extensive critique of Satz and Ferejohn, see Hausman 1995, from which the remarks in this paragraph and the next derive.
8irrelevant. What would be the point of market research and focus groups if beliefs andpreferences never mattered? Consider the best case for Satz and Ferejohn: the reactions of ﬁrmsin competitive markets to price changes or tax impositions. Except in the most intenselycompetitive industries, even the market-clearing price and quantity will not be robust to differentexplanations of the choices of individual managers. And even in intensely competitiveindustries, lots of other facts about particular ﬁrms, such as product quality, short-run proﬁts, orlevels of advertising will depend on how individuals choose. No matter how much economistswould like to escape depending on any psychological generalizations, the causal story they tell ofmarket outcomes always includes a chapter concerning how individuals choose. That chapter isoften uninteresting, and it often contributes little to our understanding of the phenomenon or toour ability to inﬂuence the phenomenon. But the chapter is nonetheless indispensable.4.2 Should economists explain dynamics?Economists rarely attempt to explain the path of adjustment to changes in the economicenvironment. Instead they explain only how the new economic equilibrium will differ from theold. Models that attempt to explain increased inequalities by lowered trade barriers compareequilibria with higher and lower trade barriers. They do not attempt to show how the effects oflowered trade barriers ripple through the economy. They do not consider the consequences ofthe many disequilibrium interactions that will take place along the way toward a new equilibrium(if indeed such is ever reached).Most economists do not welcome this state of affairs. It arises because good theories of thedynamics of adjustment are unavailable. But I would suggest that economists have becomecomplacent about this inadequacy — they have become willing prisoners of the limitations oftheir theories. One advantage of not worrying about adjustment paths is that it encouragesinattention to the details of individual choice, which may be crucial to the adjustment processeswithout (perhaps) having any very considerable consequences for which new equilibrium isreached.Economists indeed often overlook the extent to which their explanations are limited. Considersome other remarks of Hicks’: We have now…to deduce the laws of market conduct—to ﬁnd out what can be said about the way the consumer will react when prices change. Discussion of equilibrium conditions is always a means to an end; we seek information about the conditions governing quantities bought at given prices in order than we might use them to discover how the quantities bought will be changed when prices change. (1946, p. 26)This makes it sound as if Hicks is going to offer a theory of dynamics — an account of howconsumers will react, of the consequences of their reactions, the consequences of thoseconsequences and so forth. But in fact he offers only a “comparative-statics” account of how thenew equilibrium will differ from the old. Little is said about how severely this limits economics.Why are the limits so severe? In comparative statics, economists take preferences, resourceendowments and technological possibilities to be given. When there is, as in the case of thegrowth of income inequalities, an exogenous technological change or an exogenous lowering oftrade barriers, one holds ﬁxed preferences, endowments and other technological possibilities inconsidering the consequences for income distribution. But this is a reasonable ﬁrstapproximation only in the short run. Indeed Wood argues that it is not a reasonableapproximation even in the short run. He maintains that conventional calculations of the
9consequences of lowering trade barriers mistakenly overlook the search for new labor-savingtechnologies that cheap imports stimulate (1995, p. 67). It is no secret that preferences adapt andthat new technologies are sought. So the standard framework of comparative statics isappropriate only for the short run. But it is precisely in the short run that the consequences ofadjustment processes are likely to be most pronounced. Furthermore, equilibria are generally notunique. Without an account of the path leading from one equilibrium to another, there is nogeneral way to say which of the new equilibria the economy will settle in. These complaintsabout comparative statics do not, of course, remedy the inadequacies of theories of adjustmentdynamics. Demonstrating the need for such theories does nothing to satisfy that need, and it maybe that economists cannot overcome these explanatory limitations. But they could be lesscomplacent, and more research effort might be devoted to adjustment mechanisms anddisequilibrium processes.5 Causal explanation and rational criticismI have argued so far that economists need to give explanations, including explanations ofindividual choices and of dynamic processes, that these explanations are causal, and thatconsequently practical concerns with control go hand in hand with theoretical explanatoryconcerns. At this point a crucial complication enters the story. Causal explanations ineconomics typically include a link involving individual choice. If lowered trade barriers causeincreased wage inequality within the U.S., then part of the story (though admittedly anuninteresting part) involves consumer choices of cheaper imported goods over more expensivedomestically produced goods, decisions of executives to move factories to other countries whereunskilled labor is cheaper, and so forth. Explanations of those choices are, I maintain, causal: themanager of a ﬁrm or a division would like to increase its proﬁts or market share. Given thelowered trade barriers, he or she believes that goods of equal quality can be brought to markethere cheaper by moving factories abroad. The belief and the preference jointly cause thedecision to move factories abroad.But the belief and the preference do not only cause the action. They also constitute reasons forthe action. Causes are, of course, not always reasons. A tornado that causes the destruction of afactory is not a reason why the factory should be destroyed. Nor are reasons always causes: it isdifﬁcult to see how the weak reasons Iago gives for his hatred of Othello could have caused histerrible deception. But, as Donald Davidson (1963) argues, effective reasons — that is reasonsthat are actually responsible for the actions they are reasons for — are always causes. Some ofthe causes of choices that economists cite — preference orderings and expectations — arereasons, too, while others, such as some constraints, may be causes only.The fact that explanations in economics involve both reasons and causes of the action to beexplained has far reaching consequences, because reasons, unlike causes, can be appraised.There are good reasons for action and reasons that are not so good. If the causes of an action arealso good reasons to do it, then one has justiﬁed as well as explained the action. If the causes arenot good reasons, then one has raised doubts about whether the action was justiﬁed. Theevaluation here is rational or prudential, not moral. To do something that there is good reasonnot to do is to act foolishly, not necessarily immorally. But it is hard to keep what is rational andwhat is moral completely separate, and the fact that explanations of choices in positiveeconomics cite reasons is one conduit by which moral evaluations become entangled in positiveeconomics (see Hausman and McPherson 1996, ch. 4). The fact that explanations of choicesinvolve reasons also explains the peculiar fact that mainstream economics is built around atheory of rationality. This is not an optional oddity. Only rational beings can be moved byreasons. Agents must be rational (though not necessarily perfectly so) if their beliefs andpreferences are to explain their choices. It is, then, no surprise that empirical difﬁculties with the
10basic model of rationality have done so little to shake that model. The entire explanatorystructure of contemporary economics rests on the rationality of economic agents.This observation about explanation has important implications from the perspective of control.Since a factor such as a technological innovation or a lowered tariff barrier is a reason as well asa cause of a phenomenon such as increased income inequality, its operation is necessarilymediated by the beliefs and preferences of economic agents. A lowered tariff barrier that anagent expects to be temporary may have a very different consequence than a lowered tariff thatan agent expects to be permanent. A technological innovation that implies work relationships inconﬂict with local norms may be adopted slowly or rejected altogether, while another innovationthat is more compatible with “preferences” may be adopted rapidly. Arguments and valuesmatter, though how much they matter cannot, of course, be decided from the philosopher’sarmchair.6 ConclusionsEven economists whose concerns are exclusively practical should be interested in diagnosing thecauses of various phenomena, because an understanding of the causes helps one to control theireffects. If one decides that Adrian Wood is right and that lowered trade barriers are the mostimportant cause of increased inequalities, it does not of course follow that protectionism is thebest way to diminish those inequalities, and Wood himself argues against this solution (1995, p.78). But an understanding of the mechanism by which lowered trade barriers allegedly had thisconsequence helps one to identify other kinds of interventions to alleviate the problem.Regardless of one’s view of the ultimate goals of economics, explanation has a central place onthe agenda.Economists typically explain only the differences among equilibria. This is an unfortunateconsequence of the weaknesses of their theories of adjustment processes. Those theories needlots more work, because adjustment processes matter a great deal, at least in the short-run; and itis only in the short-run that typical comparative statics explanations have any reasonableapplication.The diagnoses economists give include an essential (if often uninteresting) role for individualchoices, and the diagnoses are not acceptable if their explanations of individual choice are notacceptable. Although important links in the causal chain, citing beliefs and preferences oftencontributes little to explanations, since these factors are often superﬁcial and the dependence ofthe outcomes on them is fragile. Explanations of individual choices cite the reasons as well asthe causes of choices. This fact explains why there is an ineliminable normative element withineconomics and why economic theories are constructed around a theory of rationality.There is a great deal more to be said about explanations in economics. Explanations ineconomics appear to be inexact or only approximate. They appear to involve idealizations andabstraction. They conﬁne themselves to a strikingly short list of kinds of causal factors. All ofthese issues, which are not broached here (see Hausman 1992), must be addressed by anycomprehensive account of explanation in economics. References
11Achinstein, Peter. 1983. The Nature of Explanation. Oxford: Oxford University Press.Davidson, Donald. 1963. “Actions, Reasons and Causes.” Journal of Philosophy 60: 685-700.Deardorff, Alan and Dalia Hakura. 1994. “Trade and Wages: What Are the Questions?” in J. Bhagwati and M. Kosters, eds. Trade and Wages. Washington, DC: American Enterprise Institute, pp. 76-107.Fortin, Nicole and Thomas Lemieux. 1997. “Institutional Changes and Rising Wage Inequality: Is There a Linkage?” Journal of Economic Perspectives 11(2): 75-96.Freeman, Richard. 1995. “Are Your Wages Set in Beijing?” Journal of Economic Perspectives 9(3): 15-32.Friedman, Milton. 1953. “The Methodology of Positive Economics,” in Essays in Positive Economics. Chicago: University of Chicago Press, pp. 3-43.Gottschalk, Peter. 1997. “Inequality, Income Growth, and Mobility: The Basic Facts.” Journal of Economic Perspectives 11(2): 21-40.Hausman, Daniel. 1983. “Are There Causal Relations Among Dependent Variables?” Philosophy of Science 50: 58-81._____. 1990. “Supply and Demand Explanations and their Ceteris Paribus Clauses.” Review of Political Economy 2: 168—86._____. 1992. The Inexact and Separate Science of Economics. Cambridge: Cambridge University Press._____. 1995. “Rational Choice and Social Theory—A Comment,” Journal of Philosophy 92: 96-102._____. 1998. Causal Asymmetries. New York: Cambridge University Press.Hausman, Daniel, ed. 1994. The Philosophy of Economics: An Anthology. 2nd. edn. New York: Cambridge University Press.Hausman, Daniel and Michael McPherson. 1996. Economic Analysis and Moral Philosophy. Cambridge: Cambridge University Press.Hempel, C. 1965. Aspects of Scientiﬁc Explanation and Other Essays in the Philosophy of Science. New York: Free Press.Hicks, Sir John. 1946. Value and Capital. 2nd. edn. Oxford: Oxford University Press.Lewis, David. 1986. “Causal Explanation,” in Philosophical Papers. vol. 2. New York: Oxford University Press, pp. 214-40.Miller, Richard. 1987. Fact and Method: Explanation, Conﬁrmation and Reality in the Natural and the Social Sciences. Princeton: Princeton University Press.Johnson, George. 1997. “Changes in Earnings Inequality: The Role of Demand Shifts.” Journal of Economic Perspectives 11(2): 41-54.
12Richardson, J. David. 1995. “Income Inequality and Trade: How to Think, What to Conclude.” Journal of Economic Perspectives 9(3): 33-56.Robbins, L. 1935. An Essay on the Nature and Signiﬁcance of Economic Science. 2nd. edn., London: Macmillan; excerpted in and quoted from Hausman, ed. 1994.Salmon, Wesley. 1971. “Statistical Explanation.” in Salmon, Wesley, ed. Statistical Explanation and Statistical Relevance. Pittsburgh: University of Pittsburgh Press, pp. 29-87.Satz, Debra and John Ferejohn. 1994. “Rational Choice and Social Theory.” Journal of Philosophy 91: 71-87.Topel, Robert. 1997. “Factor Proportions and Relative Wages: The Supply-Side Determinants of Wage Inequality.” Journal of Economic Perspectives 11(2): 55-74.van Fraassen, B. 1980. The Scientiﬁc Image. Oxford: Oxford University Press.Wood, Adrian. 1995. “How Trade Hurt Unskilled Workers.” Journal of Economic Perspectives 9(3): 57-80.