Desiderata for a Theory of Explanation

In order to be in a position to evaluate the relative merits of the grounding-based and grounding-free theories of metaphysical explanation, we need some independent metric against which to measure these theories. As such, here I will briefly identify some desiderata for a theory of explanation, more generally. These I have gleaned, for the most part, from the ways in which theories of scientific explanation have been criticised. So, if some theory has come under attack for failing to exhibit feature X, I take it that, for some at least, X is a desideratum. I will say a lot more about how these desiderata interact with the literature on scientific explanation in §2.5.

It will quickly become apparent that some of the following desiderata are in tension with one another. My diagnosis of this—following Bromberger (1965), Lewis (1986b) and Bird (2005)—is that there are (at least) two senses in which the word ‘explanation’ is used, which Bird (2005) calls the subjectivist and objectivist senses, but I

prefer to call the epistemic and ontic senses. In the subjectivist/epistemic sense, an explanation is something offered to an agent in order to enhance her understanding of some phenomenon. In the objectivist/ontic sense, one phenomenon can explain another without any agent ever realising that this is the case, for these explanations are there in the world, such that they obtain regardless of agents’ interests or understanding.

As Bird (2005) argues, it is plausible that these senses are interrelated. For, when we offer epistemic explanations we are trying to tap into part of the objective explanatory structure of the world so as to illuminate some phenomenon for some agent.

Nevertheless, that explanation is commonly thought of in these distinct ways is sufficient to explain why the desiderata pull in different directions. For, while most desiderata seem motivated by thinking of explanation in the epistemic sense, there is one that is

motivated by thinking of explanation in the ontic sense.

The following desiderata are motivated by epistemic intuitions about explanation.

COVERING CASES: A theory of explanation in some domain should capture the

explanations actually used in that domain. If there are explanations that are not covered, something is missing.

For example, Salmon’s (1984) causal process theory is criticised for being putatively unable to cover actual explanations in terms of absences (see §2.5.2; Beebee, 2004 for discussion). Thus, I take it that covering cases of actual metaphysical explanation is a desideratum for a theory of metaphysical explanation.

IRREFLEXIVITY: Nothing explains itself. While there may be unexplained, or unexplainable phenomena, to cite some event as its own explanation is not to explain it at all.

ASYMMETRY: Explanation is an asymmetric affair, such that if A explains B, it is not the case that B also explains A.39

The motivation for irreflexivity and asymmetry is that we, as agents, find self- explanations and circular explanations to be unhelpful in illuminating why some phenomenon is the way that it is. For instance, Hempel and Oppenheim’s (1948) deductive-nomological theory of scientific explanation is criticised (by, for example,                                                                                                                

39 _{Note that asymmetry entails irreflexivity, as a self-explanation is a case where both A explains B, and B}

Salmon, 1984) for being unable to rule out symmetrical explanations (§2.5.1). Thus, I take it that asymmetry and irreflexivity are desiderata for a theory of explanation.

UNDERSTANDING: The explanans should shed light upon the explanandum,

making the latter more intelligible. This is the most explicitly epistemic element of explanation, whereby the phenomenon in question should be illuminated by the explanans.

RELEVANCE: The entirety of the explanans should be relevant to the

explanandum. A perfectly good explanation can be ruined by the addition of extraneous, irrelevant information.40

These candidate desiderata once again reflect an inclination to think of explanations as the kinds of things that have a certain psychological effect upon agents. So, for example, the deductive-nomological theory is often criticised for allowing that the event of a storm can be explained in terms of barometer readings, which we intuit to be irrelevant (see §2.5.1).

The final candidate desideratum is strongly suggested by the ontic understanding of explanation.

OBJECTIVITY: What explains what is not an interest-relative or subjective matter. Some parts of the world explain other parts, and this is simply a matter of how the world is.

It is a desire for objectivity that motivates theories of explanation framed only in terms of laws of nature or causal processes—things that exist in a mind-independent way— rather than theories that appeal also to contingent psychological features of agents.

With these desiderata in hand, there are three points I want to emphasise. Firstly, I take the above list to be defeasible, and I am not trying to convince the reader to endorse any desiderata they do not already find intuitively appealing. As these are merely

candidate desiderata, I am happy to allow that each of us will place different weight upon each desideratum, perhaps placing no weight on some, while maintaining that others are non-negotiable. Again, my intention here is not to argue that any desideratum is required, nor indeed that the reader should have a particular attitude to any of them. I merely seek                                                                                                                

40 _{The question of whether there is a mind-independent, non-anthropocentric notion of relevance is a}

to identify some features which are often deemed good-making features of a theory of explanation. Ultimately, which theories of explanation one finds attractive will depend upon how one weights the desiderata.

Second, the reason I can stay so agnostic about whether these candidate desiderata are genuine desiderata is that there is no view on the desiderata which would lead one to prefer a grounding-based theory of metaphysical explanation over the alternatives I offer in Chapters 5, 6 and 7. If one held the view that all of the above desiderata must be satisfied, one might initially be attracted to the unfiltered grounding-based theory— indeed, in the literature on grounding and metaphysical explanation, it does seem that defenders of grounding want every desideratum to be met. This is a thought to which we shall return, for, as I shall argue in Chapter 3, the unfiltered grounding-based theory of metaphysical explanation seeks to satisfy all of the desiderata in an ambitious, but ultimately implausible, way. Thus, I hope to later show that given any plausible view on the desiderata, there is a grounding-free theory of metaphysical explanation that is preferable to the grounding-based alternative. Of note is that it is exceedingly difficult to simultaneously satisfy both the epistemic and ontic desiderata: those seeking to satisfy all of the above desiderata are asking a lot, as will emerge in the below discussion of theories of scientific explanation. Perhaps these theorists of scientific explanation realise that it is a fool’s errand to attempt to satisfy desiderata derived from differing conceptions of explanation, and thus seek to strike a balance between them.

Thirdly, I want to point out that these desiderata are aligned with features of the priority intuitions. For example, there are no reflexive or symmetrical priority intuitions. Likewise, in each case of ‘x because y’, y seems relevant to, and to increase our

understanding of, x. Significantly, however, there is nothing in the priority intuitions that explicitly implies objectivity (though one might have the further intuition that it is a mind-independent truth that ‘x because y’, as reported by defenders of the unfiltered grounding-based theory).

Via consideration of these desiderata, I will show, in Chapters 5, 6 and 7, that the Grounding-free Theory has the resources to vindicate our priority intuitions in a way that also provides the theoretical utility of a strong theory of metaphysical explanation. Recall that, as long as I can show that my preferred theories of metaphysical explanation are at least as good as the grounding-based theories, I can show that my account is better overall, since it is more parsimonious not to posit grounding relations.

Before moving on, however, we conclude this chapter with a detour via some theories of scientific explanation. The purpose of this detour is not to argue in favour of any one of the following theories. Instead, it will play the following three roles. Firstly, it will identify a useful way to categorise theories of explanation—one to which we shall often return in the following chapters. Secondly, it will identify some prototypes of various kinds of theory of explanation, to be used as templates for theories of

metaphysical explanation in the following chapters. Thirdly, it will illuminate the tension between objectivity and understanding, and thus illuminate the tension between the epistemic desiderata, on the one hand, and the ontic desideratum, on the other.