Abstract
Mechanistic explanation is at present the received view of scientific explanation. One of its central features is the idea that mechanistic explanations are both “downward looking” and “upward looking”: they explain by offering information about the internal constitution of the mechanism as well as the larger environment in which the mechanism is situated. That is, they offer both constitutive and contextual explanatory information. Adequate mechanistic explanations, on this view, accommodate the full range of explanatory factors both “above” and “below” the target phenomenon. The aim of this paper is to demonstrate that mechanistic explanation cannot furnish both constitutive and contextual information simultaneously, because these are different types of explanation with distinctly different aims. Claims that they can, I argue, depend on several intertwined confusions concerning the nature of explanation. Particularly, such claims tend to conflate mechanistic and functional explanation, which I argue ought to be understood as distinct. Conflating them threatens to oversell the explanatory power of mechanisms and obscures the means by which they explain. I offer two broad reasons in favor of distinguishing mechanistic and functional explanation: the first concerns the direction of explanation of each, and the second concerns the type of questions to which these explanations offer answers. I suggest an alternative picture on which mechanistic explanation is understood as fundamentally constitutive, and according to which an adequate understanding of a phenomenon typically requires supplementing the mechanistic explanation with a functional explanation.
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Notes
Naturally there are exceptions. For example, there is considerable debate over whether the explanations offered by dynamical systems theory are in fact mechanistic. See Zednik (2011), Lamb and Chemero (2014). Indeed, the literature on dynamical systems may in fact suggest that the tide is beginning to recede.
There are, of course, other ways of thinking about mechanisms. See, for example, Bechtel and Abrahamsen (2005), Glennan (1996, 2002), and Woodward (2002, 2003), among others. It should be noted that some formulations of mechanistic explanation do involve laws (Glennan 1996, 2002; Schaffner 1993; Woodward 2003). But the dependence on laws is a minority position. Accounts that do not involve laws (e.g., Machamer et al. 2000; Craver 2007a) have gained more traction in the literature on explanation. The consensus view seems to be that the appeal to laws is unnecessary for mechanistic explanation (Bechtel 2006, 2008; Machamer et al. 2000; Craver 2007a). For present purposes I take no stand on whether this consensus is indeed justified.
Each of these views differ in important respects, and those differences will be noted throughout. I focus on these accounts because they are representative of the literature in all of the respects that are relevant for present purposes—with few exceptions, the differences between the available accounts are not ones that make a difference here. Moreover, these views are the views that have gained the most traction in the literature.
Contextual explanation is not new; its roots can be found as far back as Aristotle’s idea that for non-aggregative systems (something that “is not a sort of heap”) the whole is more than the some of its parts. What is new is the explicit juxtaposition of contextual explanation with mechanism. Historically, this combination is novel. The mechanists of the seventeenth century—Descartes, Boyle, and others—saw mechanism as a way of avoiding appeal to explanatory practices that they found to be suspect. Of course, for Descartes, such practices were perfectly acceptable for non-natural phenomena.
He also claims that few mechanistic explanations are ideally complete, and that ideally complete descriptions of a mechanism are typically too unwieldy to be useful. However, a satisfactory mechanistic explanation will appeal to explanatory factors at levels both above and below the phenomenon of interest.
Advocates of mechanistic models, like advocates of covering law models, are faced with a dilemma: they must decide whether background conditions, inputs, and outputs ought to be understood as part of the explanation or as external to it. If they are not part of the mechanism, then there are important factors that seem to do some explanatory work but are not part of the mechanism itself. Alternatively they can be understood as part of the mechanism. This may alleviate the worry just articulated, but it raises a different problem: some third entity is required to connect the mechanism to its surrounding environment. Inputs, outputs, and background connections cannot do double duty, serving both as components of the mechanism and as the mechanism’s point of connection to the environment; some third thing is needed.
It is of course important to understand that the Craver/Machamer et al. account of mechanistic explanation can trace its origins to Salmon’s account, while Bechtel and Richardson’s and Bechtel and Abrahamsen’s account does not. For this reason, Craver is subject to a special problem, which will be discussed shortly. I do not mean to impose an association with Salmon’s account where none is intended. Nevertheless, I think that Salmon’s distinction is one worth preserving, and that any account of mechanism that aims to blend these two styles of explanation together will be ultimately confused.
The distinction between how- and why-questions needs to be distinguished from a much older distinction that is substantively different. This older distinction between how- and why-questions dates at least to Dray (1957), and was adopted by Hempel (1965), Bromberger (1966), and Suppe (1989). In this older tradition, how- and why-questions were used to distinguish between “why-necessarily” and “how-possibly” some event occurred. The focus then was on the modal distinction between these two kinds of questions. In that tradition, how-possibly questions were not always taken as a request for an explanation, but rather to express skepticism that some event was likely to occur: as in “how possibly could x have occurred?!” Here, I use the distinction between why- and how-questions to reflect the difference between requests for explanation in terms of antecedent causes (why-questions) and underlying mechanisms (how-questions).
While Craver argues that levels of mechanisms are levels of nature, that is not what is meant here; the ‘0’, ‘− 1’, and ‘+ 1’ level terminology is meant to order levels in a hierarchically organized mechanism with respect to each other; this is not meant to suggest that there are ‘0’, ‘− 1’, and ‘+ 1’ levels of nature.
Of course, the heart’s function can be described in other ways as well, so this list should not be taken to be exhaustive.
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Acknowledgements
I am grateful to Colin Allen and Carlos Zednik for many years of discussion about mechanisms, and to Antony Aumann, Zac Cogley, and Kristopher Phillips for reading and providing helpful commentary on an early draft of this paper.
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Theurer, K.L. “Looking Up” and “Looking Down”: On the Dual Character of Mechanistic Explanations. J Gen Philos Sci 49, 371–392 (2018). https://doi.org/10.1007/s10838-018-9402-7
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DOI: https://doi.org/10.1007/s10838-018-9402-7