Explanation in Archaeology: An Update

Wesley C. Salmon

Abstract: This paper presents some important recent developments in the philosophical theory of scientific explanation and considers their bearing upon issues concerning explanation in archaeology. It argues that, although the received view of Carl G. Hempel has been seriously undermined in various ways, the newer conceptions can be applied within archaeology. The result is that archaeologists now have available to them more sophisticated conceptions of scientific explanation than were available in the earlier days of the "new archaeology. "

During the last few years I have been taking a fairly close look at some recent history of philosophy of science that has a direct bearing on archaeology.! The starting point is 1948, when Carl G. Hempel and Paul Oppenheim published their epoch-making article, "Studies in the Logic of Explanation." It attempted to provide an explicit and precise account of the so-called deductive-nomological pattern of scientific explanation. In my view, this essay marks the dividing line between the prehistory and the history of philosophical work on the nature of scientific explanation. To my utter astonishment I found that this article was virtually ignored for an entire decade after its publication. Then, quite suddenly, around 1957-58, it became the SUbject of intense critical discussion. What came to be called the new archaeology has its roots in the same period. During the 1950s, Lewis Binford, one of its chief founders, was a graduate student at the University of Michigan. One of his teachers, the famous cultural anthropologist Leslie White, advised him to find out what science is all about by studying the works of philosophers of

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L. Ell/brae (ed.), Mf'/(I(II'I'/I (I (!O /Ogy, 243- 253 . © 1992 J(/(i11'I'I' 1\I'rlr/I I/III,' / 'I//JlISiJ f'i'.I', PI'tIlIN l/1I liJl' N l!liJ('f'/(illt /,I', 244 WESLEY C. SALMON EXPLANATION IN ARCHAEOLOGY 245 science. He took that advice.2 One of the key features of the new example, to explain an airplane crash the FAA looks for causes. Similarly, archaeology is its emphasis on the search for scientific explanations that to find an explanation of the abandonment of Grasshopper Pueblo, fit the deductive-nomological model. archaeologists seek the causes of the departure. Hempel and Oppenheim The Hempel-Oppenheim article is a preliminary study. Hempel (1948, p. 250), in passing, casually identified their deductive-nomological provided a much more full-blown account in his 1965 monographic essay, pattern of explanation with causal explanation. In his fully developed "Aspects of Scientific Explanation." This essay offers an induc­ theory, however, Hempel (1965, pp. 352-54) explicitly denies that causality tive-statistical pattern of scientific explanation which supplements the is in any way essential to explanation. Many philosophers have criticized earlier deductive-nomological model.3 Both of these patterns are "covering the received view in general for its neglect of causal considerations, and law models," in that each requires that explanations incorporate the in W. Salmon (1982) I argued at length for the importance of causality statement of a universal or statistical law of nature. A heavily in archaeological explanation in particular. watered-down treatment of scientific explanation was given in Hempel's The causal character of archaeological explanation has to be taken in little 1966 textbook, Philosophy of Natural Science. The general conjunction with a recognition of the basic statistical character of account-offered in full detail in "Aspects of Scientific Explanation" and explanations in the sciences-especially the behavioral sciences. In superficially in Philosophy of Natural Science-qualified, during the 60s archaeology, for example, one might appeal to the fact that a particular and 70s, as the received view of scientific explanation. It was this view hunting strategy is, in certain specific circumstances, more likely than that profoundly influenced the new archaeology. The influence can readily another to yield success. This is obviously a probabilistic relationship. be seen in Watson, LeBlanc, and Redman's Explanation in Archeology: People often maintain, of course, that underlying the statistical explana­ An Explicitly Scientific Approach (1971), the locus classicus of the new tions are deterministic causal relationships, and that we resort to statistical archaeology. Their commitment to the received view is reiterated in the considerations only because of our ignorance of these underlying causal second edition, published under the title Archeological Explanation: The relationships. My own view is that we need not make gratuitous Scientific Method in Archeology (1984). metaphysical assumptions of that sort. A more straightforward and Influential as these standpoints were, not all archaeologists were realistic approach is to try to develop a theory of probabilistic causality. persuaded by the new archaeology and not all philosophers of science A great deal of serious effort has been devoted to the elucidation of accepted the received view of scientific explanation. I shall not try to probabilistic causality, but the problem is not simple. For example, in trace the subsequent developments in archaeology, since I am not elaborating a version of probabilistic explanation that he calls aleatory qualified to do so. Nevertheless, I would like to say a little about explanation, Paul Humphreys (1981, 1983, 1989) has pointed out that, in developments in the philosophy of science concerning scientific explana­ the statistical context, we must make allowances for both contributory tion. The philosophical situation has changed markedly since the early causes and counteracting causes. In attempting to explain the abandon­ 1970s. ment of Grasshopper Pueblo, for example, we must take account of such The first point to emphasize is that the "received view" is no longer contributing factors as the occurrence of a fairly severe drought and such received. Indeed, there is widespread (though not complete) consensus counteracting factors as the existence of a highly developed stable among those actively working on scientific explanation that the. "received community. The situation becomes extremely complex when we realize view" of the 60s and 70s is basically unsound. I shall not go into the that, in some cases, two factors that qualify individually as contributing details of the philosophical arguments that have brought about this causes may, when they occur together, constitute a counteracting cause. change of attitude, but I would like to say a little about their upshot for Although one cannot say that a satisfactory account of probabilistic archaeology.4 To do so I shall briefly discuss two general approaches to causality has been developed, I think we can say that important progress scientific explanation. has been made in that direction.5 1. Causal explanation. It seems evident to common sense that, in many The recognition of causal aspects of scientific explanation does nothing cases, to explain some phenomenon is to find and cite its cause. For to undermine the covering law character of explanations. The causal 246 WESLEY C. SALMON EXPLANATION IN ARCHAEOLOGY 'I processes and interactions to which we appeal for purposes of giving an explanation, whether of a deterministic or a probabilistic sort, are well, perhaps, as economics, sociology, and psychology. Thoro NUll 1\ II Iii III governed by causal laws. the question of whether any distinctively archaeological blws ,'xll·H II lit " , 2. Explanation by unification. One idea-implicit in many works on then any legitimate archaeological explanation would have 10 (/(' p"llIl 11 11 scientific explanation, and made explicit by Michael Friedman (1974)-is laws from other scientific disciplines, and these laws wOllld Iii I 1\ /01, that science enhances our understanding of the world by providing unified unifying connections between a portion of archaeology and a l 1 \l1l1~ 1 11111 accounts of wide ranges of phenomena. Our understanding increases as other domain. Such explanations would thus exemplify the lInif'iI"III1!l" I d we reduce the number of independent assumptions required to explain archaeological phenomena with the phenomena in other rOil hllN I" a given body of phenomena. Friedman cites as an example the science, natural and/or behavioral. This must not, however, be tal«('" III kinetic-molecular theory of gases, which gives a unified account of a imply that explanatory unification cannot exist if laws peculill I II ' number of different gas laws-Boyle's law, Charles's law, Graham's law, archaeology are invoked in archaeological explanation. There might 1)( etc.-and connects them with other mechanical phenomena that can be bona fide archaeological laws that can themselves be explained by 1:lw/, explained by Newtonian physics. The search for broad unifying theories of other domains. The fact that optics is reducible to electromagJlet/1" has certainly been a major driving force in the history of science, and it theory does not imply that there are no laws of optics or that they aI'r has met with some striking successes in the natural sciences. not used in explaining optical phenomena.6 Explanatory unification often involves the reduction of one domain of Let us take a moment to compare and contrast causal explanationN science to another. When, for example, it was shown that visible light and unifying explanations. To provide a causal explanation of any given consists of electromagnetic waves that occupy a small segment of the fact, it is often necessary to get into the nitty-gritty details of the causal total spectrum of electromagnetic radiation, optics was reduced to mechanisms that produced the fact-to-be-explained. To explain the electromagnetic theory. Thereafter, it was not necessary to have two location and contents of a particular burial, for instance, it may be separate theories-one for optics and another for electromagnetic necessary to ascertain the age and gender of the individual interred, and phenomena-because Maxwell's theory of electromagnetism covered them to determine the cause of death. In constructing causal explanations it both. is necessary, in general, to infer or postulate the existence of causal The idea of explanatory unification in the behavioral sciences is more processes that are no longer available for our direct inspection. Moreover, problematic, but it has often been associated with some notion of causal explanations often appeal to entities such as atoms, molecules, or reduction. If, for example, methodological individualism is correct, then bacteria that are not directly observable under any circumstances; their psychology furnishes the fundamental explanatory theory for anthropology, observation or detection requires some sort of special apparatus. The economics, political science, and sociology. I do not intend to argue the causal explanation consists, in large part, of exposing hidden mechanisms. case for or against this sort of reductionism; I mention it only because Unifying explanations involve reference to broad structural features of it clearly illustrates the idea of explanatory unification. the world. Consider a "homey" example. A parent notices that a baby, One of the most basic issues associated with the new archaeology left in a carriage with the brake on, can move it some distance by arises from the covering law conception of scientific explanation. bumping and rocking, whereas it cannot move the carriage any significant According to this conception of explanation-which was fundamental to distance if the brake is otP One could, in principle, ca lculate tbe effect the received view-every bona fide explanation makes essential reference of each of the many causal interactions between the baby and carriage to at least one law of nature. Considerable controversy surrounded the when the brake is off, thereby providing a causal exp lana tion. Much question of whether there are any archaeological laws per se. Certainly more simply, however, we can cite the law of conscrval1on of linear archaeologists make use of various laws of nature. In radiocarbon dating, momentum-a fundamental and universal law of nature- i,O show that, for example, one appeals to the law of radioactive decay. Many other no matter what the interactions between the baby and I hu carriage, no examples could be given, involving laws of geology, biology, chemistry-as significant travel will occur. The unifying explanation till(.)W~ flow this 248 WESLEY C. SALMON EXPLANATION IN ARCHAEOLOGY 249 peculiar bit of baby/carriage behavior fits into the universal scheme of When discussing scientific explanation it is important to avoid thinking things. and talking about the unique correct explanation of any given phenomen­ Explanations in the unification style can also occur in archaeology, as on. There may, in general, be several different correct explanations of well as in other branches of the behavioral and biological sciences. any such phenomenon. There will normally be many different sets of Though the appeal may be to laws less fundamental than conservation explanatory facts from which to construct a correct explanation. This of linear momentum, that does not necessarily disqualify them. Such point is recognized, at least implicitly, by most philosophers who deal with explanations might involve fundamental principles of nutrition. It has this topic. I want to argue, in addition, that a given fact may have been pointed out, for example, that corn (maize) existed as a cultivated correct explanations of different types, in particular, correct causal crop in Arizona as early as 2000 B.c., but that it did not become a explanations and correct unifying explanations. major cultigen until 1000 to 1500 years later. The evidence suggests that If I am right in my assessment of the relationship between these two it became an important crop when beans were also available. types of explanation, we might use it to deal with a longstanding problem regarding explanation that arises, not only in archaeology, but in several The dietary needs of human organisms ... have an important other biological and behavioral sciences as well. The problem to which effect on patterns of adoption of domesticates. Corn, for example, cannot I refer is functional explanation, and the point can best be seen in the be used as a major source of protein because it lacks lysine, a major context of evolutionary biology. It should be noted, to begin with, that amino acid. Beans, however, are rich in lysine .... Corn and beans the Darwinian theory of evolution provides an overarching framework for together can form the basis of a particular population's diet in a way understanding the development of the various forms of life on our planet. that neither could alone. It is not surprising that prehistoric populations It appeals to chance mutations, the heritability of traits, the struggle for in Arizona did not seem to have begun to rely heavily on corn until survival, adaptedness to the environment, and the survival of the fittest. after beans were also present in the region. (Martin and Plog, 1973, p. It does not, however, give an account of the details of the mechanisms 284.) of inheritance or natural selection. This explanation is based upon extremely comprehensive principles of Consider some particular trait of some particular type of organism-for nutrition and biochemistry, but it does not make any attempt to fill in example, the well-known case of protective coloration of the peppered the details of the causal story of the introduction of beans to the area, moths in Liverpool. These moths live on plane trees, which have naturally or of the first efforts at large-scale corn production. In addition, as we a light colored bark. Prior to the industrial revolution the moths were shall see, explanations in terms of basic prinCiples of biological evolution light grey, but when the soot from the factories blackened the bark of qualify for membership in this category. the trees, the moths became black. We can say that the dark color has Explanation through unification seems to me, fundamentally, a way of the function of providing camouflage and thus lessening the chance of a providing understanding of some phenomenon by relating that phenomen­ given moth being eaten by birds. Those moths that have a lighter color on to a weltanschauung or overall conception of the world. This does not have a greater chance of becoming prey for birds. Thus, on average, the mean that one may pick just any world view he or she happens to feel darker colored moths tend to reproduce more frequently, and the lighter comfortable with; the picture of the world must be developed on the ones tend to reproduce less frequently. This unbalanced color situation basis of the best scientific knowledge available to us. The adequacy of with respect to progeny has the effect of producing a dark color for the any explanation by unification is not just a matter of psychological species as a whole. In this century, when the industrial pollution in comfort; the adequacy must be evaluated on the basis of objective Liverpool was cleaned up, the color of the moths reverted to light grey. scientific knowledge. But given an adequate scientific basis, such The dark color no longer functioned as effective camouflage; the lighter explanations do provide at least some measure of scientific understanding color functioned better in the changed environment. Functional explana­ of the phenomena thereby explained. tions of this sort are perfectly legitimate in the context of evolutionary biology, and they provide scientific understanding of the phenomena they 250 WESLEY C. SALMON EXPLANATION IN ARCHAEOLOGY 251 seek to explain. Although-as Larry Wright (1976) has convincingly his view of explanation as unification is a global view; the received view argued-there is an important sense in which the evolutionary explana­ was local. tion is causal, it does not give a fine-grained causal account of the Indeed, as Philip Kitcher (1985) has remarked, we can look at the two underlying mechanisms. As long as the trait of color is heritable, it does approaches to explanation-via unification and causation-as "top-down" not matter to the evolutionary account what precisely is the mechanism and "bottom up," respectively. The former looks at the entire structure of inheritance. of scientific knowledge, with special attention to its highest level theories, There is, at the same time, the possibility in principle, if not in fact, and works down from there, so to speak. The latter pays fundamental of giving a full causal explanation of the color of these moths in attention to the nitty-gritty details of the causal mechanisms, and builds biochemical terms. This type of explanation would appeal to the up from there. I see these two approaches as complementary rather than chemistry of DNA and RNA, and to the synthesis of the proteins that mutually exclusive (W. Salmon, 1990a). provide color in the surface of the organism. It is also a legitimate Scientific understanding is, I think, a rather complicated matter. It has explanation of the color of the moth. This kind of explanation does many aspects. I have discussed two of them in this paper, namely, the involve the fine-grained details of the causal mechanisms involved in the exposing of underlying causal mechanisms and the exhibition of global production of the trait in question. Wright (1976, p. 59) clearly recognizes structures. Perhaps there are others as well. Our minds should be open the compatibility of functional (or teleological) explanation and to that possibility. fine-grained causal explanation. We must realize, moreover, that there are many types of explanation The point for which I am arguing has not been widely acknowledged. that make no pretense of being scientific, but which are perfectly Indeed, traditionally-going back to the Hempel-Oppenheim paper legitimate nonetheless. An archaeologist can explain to a student how to (1948)-there has been a deep and continuing dispute between those who prepare a sample of material for radiocarbon dating. This is not an upheld the received view and those who supported a causal conception attempt to explain why some natural phenomenon occurs; it is an attempt of explanation. And the controversy was not completely ill-founded, to explain how to do something. An archaeologist can explain to a because both the received view and the causal conception have evolved mechanic what is wrong with a backhoe in the hope that the mechanic considerably from their earlier forms. It makes sense to suggest that they can repair it. Explaining what is fundamentally different from explaining are compatible in their present forms only because such developments why. An archaeologist can try to explain the meaning of a particular have occurred. decorative design on pottery in a particular cultural setting. The result Earlier versions of the causal conception suffered from the lack of any may involve a description of various psychological responses it arouses in adequate analYSis of the very concept of causality. It was often taken as members of the group. This kind. of explanation is closely akin to a primitive concept, about which we could make accurate intuitive explanations of the meanings of paintings or poems in our culture. Such jUdgments, without any need for further clarification. On the basis of explanations have aesthetic or religious significance, but they do not recent work on causality-including, of course, probabilistic causality-it pretend to furnish scientific explanations of natural phenomena. To is possible to offer a more defensible account. distinguish these other types of explanation from scientific explanations is As I see the situation, the received view has evolved into the view of not to disparage them-quite the contrary, to confuse different sorts of explanation as unification. But a significant Change has occurred in the explanation with one another interferes with the appreciation of all of course of this evolution. Whereas the received view was prepared to their importances. accept as legitimate any subsumption of a fact-to-be-explained under a So, how does all of this relate to the new archaeology? It does bona fide law of nature, no matter how narrow its scope, the newer view nothing to undermine the thesis that a basic aim of archaeology is to looks at the overall structure of scientific knowledge and judges provide scientific explanations of phenomena in its domain. The moral is explanations in terms of their ability to unify. As Friedman pointed out, that the rather simplistic and rigid notions of scientific explanation furnished by philosophers in the heyday of logical empiricism and of the 252 WESLEY C. SALMON EXPLANATION IN ARCHAEOLOGY 253

new archaeology should give way to more sophisticated and complex Hempel, Carl G., and Paul Oppenheim, 1948. "Studies in the Logic of conceptions of the nature of scientific explanations.s Explanation," Philosophy of Science, vol. 15, pp. 135-75. Reprinted in Carl G. Hempel, Aspects of Scientific Explanation and Other Essays in University of Pittsburgh the Philosophy of Science (New York: Free Press, 1965), pp. 245-95. Humphreys, Paul, 1989. The Chances of Explanation. Princeton: Princeton Notes University Press. Kitcher, Philip, 1985. "Two Approaches to Explanation," Journal of Philosophy, vol 82, pp. 632-39. 1 The results of this work appeared in (Salmon, 1990). __, 1989. "Explanatory Unification and the Causal Structure of the 2 Lewis R. Binford, An Archaeological Perspective (New York: Harcourt, World," in Philip Kitcher and Wesley C. Salmon, eds., Scientific Brace, and Jovanovich, 1972), 7-8. Explanation, vol. 13, Minnesota Studies in the Philosophy of Science 3 Hempel also introduces a deductive-statistical pattern, which is not of (Minneapolis: University of Minnesota Press), pp. 410-505. particular concern to us in this discussion. Moreover, explanations of this Martin, Paul S., and Fred Plog, 1973. The Archaeology of Arizona. Garden type can appropriately be considered a subspecies of deductive-nomologi­ City, NY: Doubleday. cal explanation. Salmon, Merrilee H., and Wesley C. Salmon, 1979. "Alternative Models 4 I have presented some of these arguments in papers addressed to of Scientific Explanation," American Anthropologist, vol. 81, pp. 61-74. archaeological audiences, namely, M. Salmon and W. Salmon (1979) and Salmon, Wesley c., 1980. "Probabilistic Causality," Pacific Philosophical W. Salmon (1982). Quarterly, vol. 61, pp. 50-74. __, 1982. "Causality in Archaeological Explanation," in Colin Renfrew, 5 Patrick Suppes (1970) offers a classic systematic treatment; W. Salmon et aI., eds., Theory and Explanation in Archaeology (New York: (1980) contains a sUlVey of various theories. Humphreys (1989) and Eells Academic Press), pp. 45-55. (1991) represent the state of the art. __, 1990. Four Decades of Scientific Explanation. Minneapolis: 6 The most advanced and thorough account, to date, of the unification University of Minnesota Press. Reprinted from Philip Kitcher and approach is given in Kitcher (1989). Wesley C. Salmon, eds., Scientific Explanation, vol. 13, Minnesota 7 For purposes of this example we must assume that the rolling friction Studies in the Philosophy of Science (Minneapolis: University of of the carriage with the brake off can be neglected. Minnesota Press, 1989), pp. 3-219. S An earlier version of this paper was presented at the First Joint __, 1990a. "Scientific Explanation: Causation and Unification," Cntica, Archaeological Congress, Baltimore, 5-9 January 1989. vol. 22, pp. 3-21, Suppes, Patrick, 1970. A Probabilistic Theory of Causality. Amsterdam: Bibliography North-Holland. Watson, Patty Jo, Steven LeBlanc, and Charles Redman, 1971. Explana­ tion in Archeology: An Explicitly Scientific Approach. New York: Binford, Lewis R., 1972. An Archaeological Perspective. New York: Harcourt, Brace, and Jovanovich. Columbia University Press. Watson, Patty Jo, Steven LeBlanc, and Charles Redman, 1984. Archeo­ Eells, Ellery, 1991. Probabilistic Causality. Cambridge: Cambridge logical Explanation: The Scientific Method in Archeology. New York: University Press. Columbia University Press. [2nd ed. of Watson, et aI., 1971] Friedman, Michael, 1974. "Explanation and Scientific Understanding," Wright, Larry, 1976. Teleological Explanations. Berkeley: University of Journal of Philosophy, vol. 71, pp. 5-19. Hempel, Carl G., 1965. "Aspects of Scientific Explanation," in Carl G. California Press. Hempel, Aspects of Scientific Explanation and Other Essays in the Philosophy of Science (New York: Free Press), pp. 331-496. __, 1966. Philosophy of Natural Science. Englewood Cliffs, NJ: Prentice-Hall.