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CHAPTER 10 Constructing Causal Explanations 1. DECOMPOSITION AND LOCALIZATION IN PERSPECTIVE Our focus has been on decomposition and localization and their role in the development of scientific research programs. We have especially emphasized their heuristic role in the construction of explanatory models within problem domains that are ill structured. In the cases we have discussed there was initially no well-delineated space of explanatory models, nor even a clearly defined range ofphenomena to be explained. The problemsolving tasks were, then, exploring and constructing the space of explanatory models, and determining the precise range of phenomena to be explained . These tasks are interdependent, their relationship neither simple nor uniform. As Ian Hacking (1983) observes, the relationship between theory and experimental "data" can change with the development of a theory and varies from one science to another. Observations may sometimes be undertaken with no particular theoretical motivation; however, the phenomena one then finds may have no clear significance, for lack of a theory to make sense of them. Alternatively, the observations' significance may become clear only after the fact. In other cases, a program of experimental investigation and observation is undertaken with clear theoretical motivations. In these instances the implications may be clear and immediate. However, on occasion the significance changes and is far from what the initial experimenter thought it would be. lt would be a mistake, from our current vantage point, to try to fit the full range of cases into a single mold. In the cases we have discussed, research programs vary greatly in both motive and method. Some motives were clearly practical: the investigation of fermentation, for example, mattered for the development of wine and beer industries, and research in genetics was not unrelated to agriculture. Other motives were more theoretical: the importance of catalytic reactions to respiration could not be clear in the absence of Lavoisier's view that respiration was a slow combustion. Even the relationship of fermentation and respiration was unclear. At times it was assumed that there should be a single, general theory encompassing both; at other times they were treated in relative isolation. Likewise, it was not always clear what the significance oflinguistic or cognitive deficits was for a theory of neural and cognitive functioning . Gall and Spurzheim rejected appeals to deficits on the grounds that Constructing Causal Explanations . 231 the resulting phenomena were unreliable and of unclear relevance to normal functioning; Broca and Wernicke made them a centerpiece of their work; Jackson acknowledged their importance, but drastically reinterpreted them; and in contemporary research their significance is still a matter of debate. In part, decomposition and localization suggest a form for explanatory models; in part, they serve to impose a structure on the phenomena to be explained. Exactly how they affect the development of explanatory models depends on the theoretical context and the available experimental techniques. We have described the explanatory models generated by these heuristics as mechanistic in character. This is meant to suggest a number of features common to the cases we have discussed. First of all, the models do feature in what are naturally thought of as causal explanations. Models describing the structure of the genetic material are meant to explain development and inheritance in terms of underlying causes. For example, the presence or absence of specific enzymes explains respiration in these terms. However, laws and theories classically construed have little place in the picture. The problems guiding the sort of research we have recounted are (1) explaining how some particular effect is actually produced, here and now, and (2) by what means. The resulting explanations are sometimes what Nancy Cartwright (1983), following John Stuart Mill (1884), calls "explanation by composition ofcauses." She says this "picture of how nature operates to produce the subtle and complicated effects we see around us is reflected in the explanations that we give: we explain complex phenomena by reducing them to their more simple components" (1983, p. 58). We describe the effect on a body, say, as the consequence of gravitational and electrical forces acting together. Likewise, we describe our linguistic competences in terms of the effect of a multitude of capacities, and we explain phenotypic traits as the consequence of the influence of genetic and environmental contributions. We explain a phenomenon that interests us by identifying a variety of causal factors and showing how they conspire to yield an effect. Second, the explanatory models appeal to what are naturally thought of as underlying mechanisms. Fermentation is something done by cells; the mechanism is...

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