Ethical Non-naturalism and the Metaphysics of Supervenience Tristram McPherson Virginia Tech dr.tristram@gmail.com Revised MS for submission to Oxford Studies in Metaethics June 28, 2011 One of the most striking recent developments in metaethics is the extraordinary revival of non-naturalistic realism about ethical properties. Not too long ago, J. L. Mackie was able to suggest that "No doubt it was an extravagance for [G. E.] Moore to say that „good‟ is the name of a non-natural quality..." (1977: 32). It would be difficult to be so dismissive today, as a growing number of influential philosophers have recently come to the defense of ethical non-naturalism.1 More importantly, these philosophers have offered sophisticated (and often competing) new ways of conceiving of non-naturalism, new and clarified arguments and motivations for these conceptions, and innovative responses to the central problems that the view has been alleged to face. One such problem is that ethical non-naturalism is unable to explain the supervenience of the ethical, where this is roughly the claim that it is impossible for two circumstances to be identical in all natural respects, but different in their ethical respects. This problem can appear difficult to finesse because the supervenience of the ethical has been a rare locus of near-consensus in metaethics. However, the idea that supervenience poses such a problem for non-naturalism has recently been challenged in a number of important ways. One central barrier to the task of evaluating these challenges is that the problem itself is typically not characterized precisely. In this paper, I propose a relatively precise and purely metaphysical interpretation of the argument that supervenience poses a substantial but not necessarily decisive problem for non-naturalism. I then canvass the prospects of various strategies for rebutting this argument on the non-naturalist‟s behalf. I argue that examining these strategies helps to illuminate the burden posed to non- 1 Some leading recent examples include Dancy (2006), Enoch (2007), FitzPatrick (2008), Huemer (2005), Shafer-Landau (2003), and Wedgwood (2007). As I will explain in §1, a number of other philosophers describe themselves as ethical non-naturalists, but defend what I take to be significantly different views. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 2 naturalism by the metaphysics of supervenience, rather than undercutting it.2 I conclude that the non-naturalist has few attractive options for responding to the problem. My central argument rests on two theses about the metaphysics of ethics and a general claim about metaphysical methodology. The first thesis is that the ethical properties are supervenient. The second thesis is that, non-naturalists are committed to the supervenience of the ethical being a metaphysically brute (i.e. inexplicable) necessary connection between distinct properties. The third claim is a modest methodological cousin of Hume‟s dictum that there can be no necessary connections between distinct existences. This is the claim that commitment to brute necessary connections counts significantly against a candidate metaphysical view. The core idea behind the central argument as I will develop it is that, while everyone should accept the supervenience of the ethical and this modest Humean thesis, the non-naturalist‟s core commitments force him to accept the bruteness of the supervenience connection. Together, these claims entail that the nonnaturalist in unable to avoid commitment to a significant theoretical liability. This is a highly schematic representation of the central argument: each of the central claims mentioned requires significant elucidation, refinement, and defense in order to make the argument precise and compelling. I approach this task in the following way. I begin by explaining the core commitments of non-naturalism (§1). I then formulate and defend a more precise version of the supervenience thesis required by my central argument (§2). This permits me to offer a more precise formulation of the central argument, and briefly motivate the remaining premises of that argument (§3). The force of these premises becomes most evident when one considers attempts to resist them, so the remainder of the paper canvasses attempts to rebut these premises. The claim that the non-naturalist must accept that the supervenience of the ethical is a brute necessity can appear to be the most vulnerable premise of the argument. I thus consider attempts to rebut it directly (§4), and by appeal to non-reductive physicalism as a model (§5). Finally, I consider attempts to cast doubt on the remaining „modest Humean‟ methodological premise (§6). 2 In this paper, I set aside the question of whether supervenience sets any special problems for antirealist metaethical views like expressivism. For contrasting views on this question, see Ridge (2007) and Sturgeon (2009). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 3 1. Characterizing classical non-naturalism In this section, I explain the characteristic commitments of ethical non-naturalism that I take to bear on the supervenience argument just introduced. As with many other philosophical views, it is controversial how best to characterize ethical non-naturalism. I will thus explain a set of core commitments that I take to be characteristic of what I will call classical non-naturalism, and contrast this view with a number of distinct views – supernaturalist, quietist, and expressivist – that are sometimes labeled „non-naturalist‟. Classical ethical non-naturalism can be characterized as the conjunction of the following two claims, suitably interpreted: EXISTENCE There are instances of ethical properties3 NEGATIVE Ethical properties are metaphysically sui generis Consider these two claims in turn, beginning with EXISTENCE. As I have characterized it, non-naturalism is a thesis about the ethical. Provisionally, I will say that ethical questions are normative questions concerning action, agents, and outcomes, where the paradigmatic ethical question is the question of what one ought, all things considered, to do. There are deep difficulties inherent in attempts to offer a more satisfactory characterization of the ethical.4 I will set them aside, because they are not the focus of this discussion: the sorts of issues that I will raise face both non-naturalism about morality more narrowly understood, and non-naturalism about normativity understood more broadly to encompass epistemic as well as practical norms.5 3 A more accurate but awkward formulation would read: „the correct metaphysics is (non-deflationarily) existentially committed to the ethical‟. The reference to ethical properties is intended only as a convenient but dispensible way to register such existential commitment. Thus, (although it would be a peculiar combination), ethical non-naturalism is in principle compatible with a Quinean view that avoided quantifying over properties, but allowed us to talk about our existential commitments concerning certain classes of entities, etc. An important discussion that argues for the significance of such broader metaphysical debates in this context is Ridge (2007), which suggests that Shafer-Landau‟s version of non-naturalism is best developed within a trope metaphysics. 4 Among others, these difficulties include questions about whether the normative and „descriptive‟ elements of thick ethical terms, like „justice‟ or „courage‟ can be disentangled from each other, and questions about how to categorize logically complex sentences or properties that have both ethical and descriptive elements, as in A. N. Prior‟s famous examples like "either tea drinking is common in England, or all New Zealanders ought to be shot." (1960: 202). 5 Some of the philosophers I discuss in this paper talk about the supervenience of the moral, the evaluative, or the normative. Because the issue at the heart of this paper cuts across those discussions, I will sometimes talk about those views as discussing the supervenience of the ethical, for the sake of uniformity. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 4 EXISTENCE conveys the fact that classical non-naturalism is an ontologically committal metaethical view. Most obviously, this view makes non-naturalism inconsistent with nihilist views in moral ontology, such as thoroughgoing error theory about ethical discourse. Such an error theory takes our ethical discourse to purport to be ontologically committal, but takes the world to be uncooperative. Very roughly, on this view, ethical discourse is of a piece with naïve talk of dragons and unicorns. Importantly, I intend a reading of EXISTENCE which also rules out certain expressivist or quietist views that have sometimes claimed the non-naturalist label. On a leading interpretation, expressivism takes the fundamental function of instances of ethical discourse to be to express evaluative attitudes, rather than to track ethical facts or properties.6 Some expressivists argue that a quasi-realist version of expressivism permits one to „earn the right‟ to apparently ontologically loaded talk. Allan Gibbard (2003: 32), has suggested further that his expressivism makes good sense of the idea that ethical concepts are „non-natural‟. Another recently popular view in metaethics is a sort of quietism which rejects expressivism but which echoes the quasi-realist‟s denial of substantive metaphysical commitments about ethics.7 In contrast with both of these views, the classical non-naturalist takes there to be ethical facts or properties in a metaphysically significant, non-deflationary sense. Distinguishing classical non-naturalism from these views is essential, because, in light of this difference, the latter views are associated with radically different motivations, theoretical assets, and liabilities.8 The non-naturalist‟s second characteristic claim – NEGATIVE – is that ethical properties are metaphysically sui generis. This claim again requires explication. The classical non-naturalist‟s claim that ethical properties are sui generis should be read as ruling out at least two relations between ethical and non-ethical properties. First, it should be read as ruling out the view that ethical properties are distinct from, but reducible to, 6 This crude characterization of expressivism clearly requires refinement. The leading systematic discussions of the relevant issues include Gibbard (2003) and Schroeder (2010). 7 Scanlon (1998: 55-64); (2003); and his second Locke lecture) is the leading example of a quietist in this sense who simultaneously claims to be a non-naturalist realist. I discuss this view in detail in my (2011). 8 Gibbard claims that his account of non-naturalistic concepts gives us all that we could want by way of satisfying some of the central motivations of non-naturalism. However, he rejects classical non-naturalism exactly because of what he takes to be its characteristic theoretical liabilities. For an argument that Gibbard‟s quasi-realism fails to accommodate the non-naturalist‟s central motivations, see FitzPatrick (2010: esp. §2.4). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 5 non-ethical properties.9 Second, it must rule out at least some views that are often described as non-reductive. For example, Richard Boyd suggests that goodness might be a „homeostatic cluster property‟. On Boyd‟s account, goodness is not reducible to any other property.10 However, there are robust (if defeasible) natural tendencies to unify the properties which together constitute the property of goodness (1997: esp. 116-18 and 122). Schematically, Boyd‟s idea is that „good‟ picks out an empirically discoverable and nomically robust pattern in the world. While goodness on the Boydian account cannot be reduced to any other property, it is not sui generis. Rather, it is metaphysically continuous with other classes of natural properties, because its nature is to be understood in terms (natural kinds, causation, homeostatic feedback, etc.) that are themselves deeply naturalistic. Non-naturalism as I will understand it rules out this sort of continuity between ethical and non-ethical properties.11 One might think that NEGATIVE overcomplicates matters: why not just say that on this view, ethical properties are not natural? While obviously intuitive, this suggestion would be misleading. Perhaps the leading account of the natural takes natural properties to be those properties discoverable by scientific investigation.12 However, most nonnaturalists intend to commit themselves to something stronger than the denial that ethical properties satisfy this criterion. Here, it is helpful to contrast the classical non-naturalist with the ethical supernaturalist. For example, some philosophers think that ethical facts and properties can be understood as a function of facts and properties of God‟s will (e.g. Adams: 1999). Such views are clearly not naturalistic in any ordinary sense of the term. 9 For what I take to be persuasive arguments that reduction shouldn‟t be understood simply as property identity, see Gillett‟s discussion of „compositional‟ reductionism (2007) and Schroeder (2005: 9-12). 10 Note that some views of reduction would count Boyd‟s view as reductive. Whether continuity of the kind I go on to describe is possible without reduction is controversial; here I set aside important debates about necessary conditions on reduction, but see the discussion in §5 for ties to debates about non-reductive monism. 11It is not entirely clear that all self-described non-naturalists satisfy this criterion. But see §5 for discussion that suggests they should. Wedgwood‟s avowedly Platonist metaphysics of the normative suggests a further way in which NEGATIVE may need to be further refined. According to Wedgwood, normative and intentional properties are essentially mutually constituting: the nature of each makes ineliminable reference to the other (2007: Ch.7). If such mutual property constitution is possible, then it is plausibly sufficient for nonnaturalism that the ethical be a member of a cluster of mutually constituting property-types, and that this cluster is sui generis in the sense described above. 12 Compare Moore (1903: 40). Other important approaches characterize the natural in terms of those properties to which we lack a priori access (compare Shafer-Landau 2006), or in terms of those properties that could feature in causal explanations of our having access to them (compare Smith 2004). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 6 However, these views (like quasi-realism) have very different theoretical motivations, assets, and liabilities from classical non-naturalism, and are thus best treated separately.13 In this section I have characterized what I take to be the core commitments of nonnaturalism, once the classical version of this view has been distinguished from radically different metaethical views which sometimes share the name. (In the rest of the paper, I will typically revert to calling the classical view „non-naturalism‟.) On the one hand, nonnaturalists take there to be actual instances of ethical properties, where this commitment is not to be given a deflationary paraphrase. On the other, non-naturalists take such properties to constitute a distinct, sui generis property kind: one that that is neither reducible to nor continuous with any other type of property. These features of the view will be crucial to my discussion of why supervenience constitutes a burden for nonnaturalism. Before proceeding to that discussion, however, I will clarify the supervenience thesis that I take to be at stake, and why we should accept it. 2. The supervenience of the ethical My aim in this section is to formulate a version of the claim that the ethical is supervenient that satisfies two desiderata. First, the supervenience of the ethical is often taken to be close to being common ground in ethics. I thus aim to offer a formulation that is modest enough to respect this thought, by being extremely difficult for at least metaethical realists to resist. Second, I require such a thesis to be strong enough to star in the central argument against non-naturalism that I will go on to offer. It is common for metaethicists to formulate the supervenience of the ethical in roughly the following way: CRUDE SUPERVENIENCE No metaphysically possible world that is identical to a second world in all natural respects can be different from the second world in its ethical respects. 13 G. E. Moore is instructive here. He famously contrasted what he took to be the non-natural character of ethical properties with both naturalist and supernaturalist proposals. Moore is willing to describe the „metaphysical‟ (i.e. supernaturalist) ethicist as purporting to offer truths about „non-natural existents‟ (1903: 112). He is thus sensitive to Sturgeon‟s point that it arguably does violence to the word „non-naturalism‟ to deny that supernaturalist views are non-naturalist (2009: 63). However, Moore thinks that the naturalistic fallacy applies as much to such proposals as it does to naturalistic accounts of morality (1903: 39). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 7 I will go on to suggest that CRUDE SUPERVENIENCE needs to be modified. However, we can begin by noting that it is a very strong metaphysical claim. First, in the standard jargon, it is a kind of global supervenience claim: it is a claim about the possible structure of whole worlds, not of the relationships between properties of individuals.14 Second, the modality invoked in this thesis is metaphysical, and not, for example, merely nomic: the idea is not that the laws of nature link certain classes of properties, but that the link between these classes of properties holds across every possible world.15 Given its metaphysical strength, we might wonder why so many philosophers are inclined to accept something like CRUDE SUPERVENIENCE. I take ethical supervenience theses to be best motivated by a two-part process. The first stage is to consider particular instances of what they rule out. For example, it seems impossible that another world might be identical to this one except that in the other world, a genocide otherwise identical to the actual Rwandan genocide differed solely in being ethically wonderful, rather than being an atrocity. Cases like this postulate a necessary connection: we seem to have discovered on reflection that the ethical features of the genocide cannot vary independently of its other features. Reflection on such examples thus suggests commitment to a series of „specific supervenience facts‟, each of which involves a posited necessary connection.16 The second stage of the process involves noticing that our views about these specific cases do not seem to rest on idiosyncracies of the cases: analogous specific supervenience facts about everyday promising, for example, seem as compelling as such facts about radical evil like genocide. This point can encourage the inductive thought that it is impossible for there to be a case in which supervenience fails. After all, what would such a case look like? Finally, given specific supervenience facts, the existence of a general supervenience thesis like CRUDE SUPERVENIENCE is explanatorily attractive: rather than having to explain a huge raft of specific necessary connections, one will have only a single general necessary connection to explain. This in turn suggests the hope of being able to explain this connection in terms of quite general features of ethical properties. While our 14 For important worries about the formulation of global supervenience claims, see Leuenberger (2009). In light of these worries, it may be that the supervenience of the ethical is better formulated in terms of strong supervenience. I set aside these concerns here. 15 This contrast will evidently disappear on views on which the laws of nature are metaphysically necessary. 16 For an ambitious use of such specific supervenience facts, see Horgan and Timmons (1992: §2). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 8 intuitive judgments about the absence of counterexamples is sadly fallible (a point shown, most famously, by Gettier), the intuitiveness of the generalization, combined with its potential explanatory force is quite powerful.17 As Nicholas Sturgeon has recently shown, however, there are excellent grounds for rejecting the idea that CRUDE SUPERVENIENCE could be dialectical common ground in metaethics. Sturgeon‟s point is simple. He accepts CRUDE SUPERVENIENCE, but he suggests that his reasons for doing so are parochial, being explained by the fact that he himself is an ethical naturalist. By contrast, a theist is likely to think that some supernatural properties are ethically significant. For example, he suggests that such a theist would presumably think that what God wishes is ethically significant (2009: 62-3).18 Sturgeon extends this point to cast doubt on common formulations of the supervenience of the ethical on the non-evaluative, the factual and the descriptive, among others. His conclusion is that different philosophers‟ seemingly shared commitments to supervenience theses simply reflect their various „parochial‟ commitments. Rather than being an independently plausible constraint on metaethical views, then, the supervenience of the ethical is actually a collection of distinct theses, none of which has wider dialectical significance (2009: 53-57). Sturgeon is to be lauded for sharply posing an illegitimately neglected question in metaethics. As he correctly points out, even some of the most careful philosophers often talk about the supervenience of the ethical on the natural, as if the sorts of difficulties in formulation that he canvasses do not exist. However, I do not think that his diagnosis of the 17 This way of understanding the motivation for accepting the supervenience of the ethical seems to me to cast doubt on the role that Blackburn takes supervenience to play in a general puzzle for ethical realists. Roughly, according to Blackburn (1993), it is puzzling that we can accept the general supervenience of the ethical without accepting as uncontroversial any specific view about which natural properties necessitate which ethical ones. However, if our commitment to supervenience is largely grounded in an elegant and seemingly undefeated generalization from uncontroversial cases, this combination of views is not particularly puzzling. What would be puzzling would be agnosticism about all specific supervenience claims, combined with acceptance of a global supervenience thesis. 18 One worry about Sturgeon‟s version of this objection is that he accepts the thesis that if God possibly exists, then He exists necessarily (2009: 66). This might suggest that all supernatural properties are necessary if possible. However, if this were so, then Sturgeon‟s own argument that CRUDE SUPERVENIENCE is parochial collapses: a theist‟s commitment to God‟s necessary existence and character is compatible with insisting that every world ethically different from our own must be naturally different too. It seems strange to think that there are no contingent non-actual supernatural beings, however. (Think of Zeus. The only reason I can think of for Zeus‟ existence being impossible is if the God of the philosophers were actual, and Zeus‟ existence were incompatible with His nature.) Note that naturalists who accept the possibility of ethically significant interactions between such supernatural beings will therefore need to reject CRUDE SUPERVENIENCE. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 9 problem is correct. Indeed, I will now introduce and defend just the sort of supervenience thesis that Sturgeon is skeptical of: a thesis that at least all ethical realists ought to accept, that permits philosophers to argue from supervenience with the sort of dialectical force that such arguments have been traditionally taken to have.19 My formulation, which may appear slightly baroque,20 draws on the same core idea that motivated my preferred formulation of non-naturalism: the idea that for nonnaturalists, ethical properties are sui generis. Call a property ethically involving if it either is a sui generis ethical property, or its real definition ineliminably mentions sui generis ethical properties. Finally, call any property a base property, unless it is an ethically involving property. This machinery permits us to formulate an improved version of the supervenience thesis: SUPERVENIENCE No metaphysically possible world that is identical to a second world in all base respects can be different from the second world in its ethical respects. 19 Ridge (2007: §2) offers a competing „ecumenical‟ response to Sturgeon. According to this proposal, the normative supervenes on either the non-normative or the descriptive, where the „descriptive‟ is characterized in roughly the terms offered by Jackson (1998). One problem with this is that it is not at all clear that, as Ridge suggests, it is undeniable "...that that the normative either supervenes on the non-normative or on the descriptive" (2007: 334). Anyone (including an ethical naturalist) could simply deny supervenience on the descriptive, because they find insuperable difficulties with Jackson‟s attempt to characterize the descriptive (for example, compare Sturgeon 2009: 75-9). Further, as Sturgeon notes, there are reasons for certain reductive naturalists to resist the claim that the normative supervenes on the non-normative (2009: 69-72). There thus appears to be no barrier to such a reductive naturalist denying both supervenience on the nonnormative and on the Jackson-descriptive. 20 I am indebted to Daniel Nolan for pressing me about A. N. Prior-style conjunctive or disjunctive properties, which led me to this slightly more complex formulation. It is worth explicitly addressing two Prior-inspired worries about the revised formulation. On the one hand, one might worry that in an ethically barren world, a mountain could have the property of being tall or evil solely in virtue of being tall, and hence that such a property in such a world is not ethically-involving. However, I take it that to state the real definition of being tall or evil, one would have to invoke ethical properties, and hence that the property is ethically involving in the sense that I am interested in. On the other hand, this latter consequence might seem to be unacceptable: how could the mountain, simply in virtue of being tall, have the property of being tall or evil (which is ex hypothesi ethically involving)? Doesn‟t this violate Hume‟s Law, which famously proscribes deriving an „ought‟ from an „is‟? It does not, for the simple fact that „ethically involving property‟ is a term of art. It is meant to finesse Prior‟s challenge in this context, not to solve it. The objection arises from missing the fact that the „ethically involving property‟ does not mean the same thing as „ethical property‟: for one thing, if ethical naturalism is true, there are many ethical properties and no ethically involving ones! Far from violating a plausible version of Hume‟s Law, the notion of an ethically involving property was introduced in a way that renders trivial the entailments from non-ethically involving properties to ethically involving properties. I thank a reviewer for Oxford Studies for pressing me to clarify this point. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 10 SUPERVENIENCE should be common ground between ethical realists.21 Consider: if naturalistic ethical realism is true, ethical properties are not sui generis. So, ethical properties will count as part of the base for a naturalistic realist, and SUPERVENIENCE is secured trivially. If non-naturalist realism is true, then ethical properties are sui generis properties, and SUPERVENIENCE entails that they supervene on a set of distinct base properties, just as the non-naturalist typically claims.22 Part of my goal in formulating SUPERVENIENCE is to offer a thesis that is as modest (and hence widely acceptable) as possible, compatible with the role of this thesis in my central argument. It is thus worthwhile to emphasize four important respects in which this thesis, as I intend it to be read, is modest. First, some philosophers suggest that in order to make a supervenience claim interesting, we must specify a subset of the natural properties as the supervenience base, because some natural properties seem by their nature to be ethically irrelevant.23 It is true that some natural properties are ethically irrelevant at least some of the time. To adapt a classic example, SUPERVENIENCE is compatible with the ethical significance of the Rwandan genocide being sensitive to the spatial location of an atom on Mars. Given such examples, the objector suggests that we want a supervenience thesis whose supervenience base rules out such absurd sensitivities. While possession of such a thesis would clearly be valuable, there are two reasons to reject the demand to produce such a thing. On the one hand, any attempt to specify the exact relevant properties will in effect constitute an attempt to do substantive normative ethics, and hence will not be nearly as uncontroversial and 21 This thesis should also be trivially acceptable to most anti-realists, since on antirealist views, there is no way for two worlds to be distinct in ethical respects. Again, some antirealists may take ascriptive supervenience theses to be more explanatorily important than ontological ones (compare Klagge 1988), but this is no barrier to their accepting SUPERVENIENCE. Some delicacy would be required in interpreting and assessing the thesis given certain quasi-realist views, and I set that task aside here. 22 A reviewer for Oxford Studies worries that the supernaturalist alternative raised by Sturgeon also plagues my formulation. Might not two worlds differ only in that the first contains an essentially good being lacking in the second? And might such worlds thereby be base-identical but ethically distinct? If so, then we would have a counterexample to SUPERVENIENCE. However, good character (and, a fortiori, essentially good character) surely supervenes on possession of some base properties: for example, an essentially good being must have dispositions to help and to refrain from harming in a certain wide range of circumstances. So, if the second world is base-identical to the first, it must contain a being with identical base properties to those that subvene the essential goodness of the being in the first world. But the intuition that supports the supervenience of the ethical is that to have those base properties guarantees that one is essentially good. This entails, contrary to the objection, that the two worlds must be ethically identical as well. 23 Compare Griffin (1992: 314). Griffin further develops his objections to the supervenience of the ethical in his (1996). For important responses see Smith (2004) and Wedgwood (2007: 149-151). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 11 dialectically compelling as SUPERVENIENCE as I have set it out. On the other, such more informative supervenience claims are simply not needed in order to spell out the burden that I shall argue faces the non-naturalist. Note further that philosophers might disagree heatedly about (a) which types of property are possible or sui generis, and (b) whether a given type of property is ethically significant. For example, one might believe that supernatural properties are actual, possible, or impossible, and one might further think that, whether they are possible or actual, such properties are not ethically significant. For example, Sturgeon suggests that on his view supernatural properties are impossible (2009: 66). So, Sturgeon might accept something stronger than SUPERVENIENCE. However, even if this is so, what Sturgeon accepts entails SUPERVENIENCE. As this example shows, disagreements of types (a) and (b) will make no difference to whether a philosopher accepts SUPERVENIENCE. These features are virtues of SUPERVENIENCE, because the supervenience of the ethical is, on the traditional view that I seek to vindicate, exactly supposed to be common ground between philosophers with radically different commitments in metaphysics and ethics.24 Second, my claim about SUPERVENIENCE is purely metaphysical. I have made no appeal to the alleged apriority or analyticity of this thesis, although the thesis as stated is compatible with commitment to these.25 I again take this to be a virtue because such claims are arguably more controversial than the thesis as sketched, since many philosophers reject the categories of apriority and analyticity on broad metaphilosophical grounds. Third, the supervenience thesis that I defend here is non-symmetric. The early discussion of supervenience both in metaethics and in the philosophy of mind often used it as a kind of proxy for an asymmetric metaphysical dependence relation. However, such dependence claims exceed the content of supervenience theses, as is now generally 24 Someone might be tempted here to the complaint that SUPERVENIENCE is „gimmicky‟, in virtue of simply expressing the disjunction of the naturalist‟s and the non-naturalist‟s commitments. I think this would be a mistake. However, as I have been emphasizing, the fact that various philosophers would in fact accept various stronger metaphysical claims is irrelevant to the use that I plan to make of SUPERVENIENCE. It is also notable that, if one were agnostic between ethical naturalism and non-naturalism, one should still be confident that SUPERVENIENCE is correct, because supervenience-violating non-naturalism is a markedly less plausible view than non-naturalism itself. 25 The burden sketched thus contrasts markedly with the canonical argument offered in Blackburn (1993), which uses the alleged conceptual status of the supervenience claim as part of an argument against ethical realism generally. For what I take to be a largely convincing argument against Blackburn‟s idea that supervenience raises problems for naturalistic realism, see Dreier (1992). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 12 recognized.27 The non-symmetric nature of supervenience theses can be illustrated by noting that every property supervenes on itself, and on any set of properties containing it. Thus, the fact that SUPERVENIENCE is non-symmetric also entails that it need not relate distinct properties.28 This point is again crucial to SUPERVENIENCE being common ground, this time helping to accommodate certain aggressively reductive views about the metaphysics of ethics. Finally, some philosophers seem to think that, in order to deserve our allegiance, a supervenience thesis must be explanatory.29 However, except insofar as one might interpret the unification provided by a general supervenience thesis to be an explanatory gain over a collection of specific supervenience theses, nothing in my quick gloss on why one might accept a supervenience thesis suggests that an ethical supervenience thesis ought to have explanatory power. To the contrary, the very heart of the argument to come is that the supervenience of the ethical appears to demand to be explained by further facts about the metaphysics of ethics.30 I take SUPERVENIENCE, so clarified, to be an adequate response to Sturgeon‟s challenge: it does deserve the sort of wide acceptance (at least among ethical realists) that the supervenience of the ethical has traditionally elicited. However, it should be emphasized that, even if it should turn out to fall to counterexamples, as CRUDE SUPERVENIENCE did, it is not at all clear that the role of supervenience in the central argument to come would be impugned. This is because actual non-naturalists, from G. E. Moore to Russ Shafer-Landau are (for just the sorts of reasons suggested by the genocide example) committed at least to the parochial claim that the ethical properties supervene on the non-ethical properties.31 Indeed, they sometimes insist that variance in these subvening properties plays a crucial role in explaining the variance in supervening ethical properties.32 Thus, even absent an uncontroversial supervenience thesis, there may be a dialectically 27 For an especially clear discussion see McLaughlin and Bennett (2008: §3.5). 28 Contrast Shafer-Landau (2003: 90), among others. 29 This seems to be the heart of Raz‟ doubts about supervenience in his (2000: 55). 30 Because the order of discovery and the order of metaphysical explanation are two very different things, it thus seems illegitimate to insist (as Raz seems to suggest) that we should abandon a confidently held general principle simply because its explanatory basis is currently opaque to us. 31 See for example Moore (1998: esp. 55-57), Shafer-Landau (2003: 78), and FitzPatrick (2008: §10). Raz (2000) is an important exception. 32 Compare Audi: "...certain of the natural properties of a thing determine what moral properties it has, (if any)" (1997: 97; emphasis mine). See also FitzPatrick (2008: 186-7). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 13 effective version of the argument to come. In what follows, however, I will assume that my formulation is sound. 3. Brute necessities: the central argument stated With non-naturalism and the supervenience of the ethical characterized, we are now in a position to introduce my central argument for the claim that supervenience entails a significant burden for non-naturalism. This argument can be encapsulated in three central theses: SUPERVENIENCE No metaphysically possible world that is identical to a second world in all base respects can be different from the second world in its ethical respects. BRUTE CONNECTION The non-naturalist must take the supervenience of the ethical properties on the base properties to involve a brute necessary connection between discontinuous properties MODEST HUMEAN Commitment to brute necessary connections between discontinuous properties counts significantly against a view Together, these three theses entail that non-naturalism is committed to brute necessary connections that count significantly against its plausibility. We have seen the case for SUPERVENIENCE in the previous section. In the remainder of this section, I will elaborate on and motivate the remaining theses, beginning with MODEST HUMEAN. MODEST HUMEAN is a methodological cousin of a metaphysical thesis that is sometimes called Hume‟s dictum: the claim that there are no metaphysically necessary connections between distinct entities. Hume‟s dictum is a common, if controversial, player in contemporary metaphysical debates. It is usually motivated on directly intuitive grounds: for example, via the claim that the relevant connections are „unintelligible‟ (e.g. Lewis 1983: 366). Despite its intuitive pull, there are a number of reasonable grounds for suspicion in Hume‟s dictum, of which I will mention two.33 First, one might worry about our ability to type entities as distinct in a way that makes the dictum true but interesting. After all, a variety of seemingly non-identical properties are necessarily connected. For example, a 33 For an important recent attack on Hume‟s dictum that examines these issues much more thoroughly, see Wilson (2010). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 14 surface‟s being scarlet is not identical to its being red, and yet seems to necessitate it. Second, one might, on quite general methodological grounds, be suspicious of the idea that we could be entitled to rule out a theory on this intuitive basis. We do not seem entitled to be sure that no theoretical package could come along that seemed so attractive on other grounds that we would yield the Humean principle. The MODEST HUMEAN thesis is modest exactly in seeking to accommodate these two grounds for concern about Hume‟s dictum. It includes two elements that address the first concern. First, consider the question of what makes two properties count as distinct. Here MODEST HUMEAN adopts the same criterion that I used to characterize non-naturalism in §1: two properties are discontinuous just in case neither is reducible to the other and they are not identical or metaphysically continuous with each other. Second, MODEST HUMEAN only applies to brute necessary connections. Thus, if it two properties are discontinuous, but we are nonetheless able to offer a compelling explanation of the necessary connection between them, MODEST HUMEAN makes the reasonable suggestion that having made such a connection intelligible would be enough to defeat the Humean presumption. MODEST HUMEAN adresses the second concern by stating only that positing the relevant brute connections counts significantly against a view, rather than ruling it out. By doing so, it signals that the other features of an overall theoretical package could (at least in principle) entitle one to belief in a theory that posited such brute connections. It is worth noting at this stage why naturalistic realists do not face a version of my central argument. MODEST HUMEAN is a completely general methodological claim, and I have suggested in §2 that naturalistic realists should accept SUPERVENIENCE. The crucial contrast is that nothing like BRUTE CONNECTION is prima facie plausible in the naturalist‟s case, because they will appeal to identity, reduction, or continuity relations to underwrite the necessary connection between ethical and base properties.34 It might in practice be quite challenging to state the relevant relations, but that is a different matter from it being hard to see in principle how it could be done. 34 The case of identity and reduction should be clear enough, here. However, it is less obvious that a continuity relation will do the required work. For one model, see §5. I do not mean to rule out the possibility that there could be forms of non-reductive naturalism that do face the same burden as the nonnaturalist. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 15 Why then should we think that the non-naturalist is committed to BRUTE CONNECTION? The case is clear, but less compelling than that for MODEST HUMEAN. In being committed to ethical properties being sui generis (as I argued in §1), the nonnaturalist is committed to them being distinct in the sense mentioned in BRUTE CONNECTION and MODEST HUMEAN. The thought motivating BRUTE CONNECTION is that, in virtue of their being distinct in this way, we have prima facie reason to think that there could be no metaphysically satisfying explanation of the necessary connection between them. What, after all, could explain such a connection? Such argument by rhetorical question is hardly satisfying, and that makes it natural to take BRUTE CONNECTION to be the most vulnerable premise of the central argument. The key gap is that being distinct in the sense set out in §1 – the failure of identity, reduction, and metaphysical continuity relations – does not seem in any obvious way to imply the lack of a possible explanatory connection. The most natural way to build on this point in order to attack BRUTE CONNECTION would be by providing an account of the relevant connection. The next two sections of this paper will thus examine the prospects of important models for undercutting BRUTE CONNECTION. I take considering such attempts to also be the best available way to defend this thesis: the failures canvassed below have a systematic character, and this significantly augments the slim intuitive case for BRUTE CONNECTION just sketched. 4. Direct attempts to undercut BRUTE CONNECTION In this section, I examine three representative strategies that aim to directly undercut BRUTE CONNECTION, by adding additional structure to the non-naturalist‟s fundamental commitments.35 The first strategy suggests that the supervenience of the ethical is not brute because it can be given an ethical explanation. The second claims that it can be given a 35 Ralph Wedgwood suggests another important way for the non-naturalist to develop this strategy in his (2007: Ch. 9). Wedgwood argues for a non-standard conception of metaphysical modality that permits him to claim that contingent facts about the actual world can affect what is possible relative to the actual world. He uses this conception to argue that he can explain the supervenience of the normative on the natural, without compromising the robustly irreducible nature of normative properties. I argue that this approach ultimately falls afoul of our intuitive commitments concerning supervenience in my (2009: 74-8). See also Schmitt and Schroeder (forthcoming) for a helpful and technically rigorous critique of Wedgwood‟s distinctive strategy. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 16 conceptual explanation. Finally, the third proposes that it can be given a constitutive metaphysical explanation. I will argue that these strategies either fail to undercut BRUTE CONNECTION or (in the third case) merely relocate the explanatory burden they are intended to alleviate. First, it is sometimes suggested that the supervenience of the ethical can be adequately explained ethically. As Matthew Kramer puts the idea: When a moral realist is pressed for an explanation of the phenomenon of supervenience, he or she should advert to the factors that have just been broached. That is, an appropriate account of the phenomenon is an ethical account that focuses on the phenomenon‟s ethical rationale. (2009: 352-3) There is something attractive about this line of thought. It can perhaps seem that our reaction to the possibility of an otherwise identical genocide being good is moral revulsion, not metaphysical incomprehension. It may be that at least some of us believe in supervenience because of our first-order normative ethical reflection, but it is crucial to distinguish the epistemological and metaphysical orders of explanation here. Our question is the metaphysical one. In evaluating Kramer‟s proposal, it is useful to recall the contrast between the classical non-naturalist and the quietist and quasi-realist.36 The quietist and quasi-realist typically claim that facts about (deflationarily understood) ethical properties are to be understood as mere reflections of ethical truths, or ethical thought and talk. It is thus easy to see why, on such views, the supervenience of the ethical will thus itself most plausibly be explained by appeal to ethical truths, or facts about ethical thought and talk. The classical non-naturalist, by contrast, thinks that ethical properties exist in a robust, not-to-be-deflated, sense. On the classical non-naturalist‟s interpretation, then, SUPERVENIENCE is a claim about the actual and possible distribution of those properties. For Kramer‟s proposal to be available to the classical non-naturalist, facts about the existence and distribution of such metaphysically robust properties must be capable of being explained by appeal to ethical truths. But this is a puzzling suggestion. The idea that in a certain domain truths explain the distribution of the properties (rather than vice-versa) looks remarkably like a way of characterizing a deflationary view about that domain. The 36 Note that Kramer himself is perhaps best understood as a kind of quietist, so the following is not intended to be forceful ad hominem. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 17 classical non-naturalist who wants to adopt Kramer‟s proposal will thus have to explain why a non-deflationary conception of ethical properties does not instead entail that ethical claims are true in virtue of the distribution of ethical properties (and perhaps, in the case of contingent ethical truths, other facts about the way things actually are).37 Second, one might think that we can undercut BRUTE CONNECTION by offering a conceptual explanation of the supervenience of the ethical. This is again an attractive thought, as many philosophers have thought that ethical supervenience theses have a „conceptual feel‟. Consider an instance of this line of thought: Phillip Stratton-Lake and Brad Hooker suggest that if we accept the buck-passing account of value, then: It is a conceptual truth that that if you have a reason to care about A, then there must be something that provides that reason. This something is what the reason supervenes on. If the reason you have to go for a walk is that it will be pleasant, then this reason supervenes on the pleasantness of the walk.... Reasons supervene on other properties because there must be something that provides the reason. There is nothing mysterious about this, nothing here that stands in need of further explanation. (2006: 164) The core of this argument appears to be that, on the buck-passing view, the supervenience of normative facts on non-normative facts is a conceptual truth, and hence is not brute. The central point to note in response is that we do not as a matter of language, get to simply stipulate necessary connections between distinct properties.39 We don‟t get to stipulate, for example, that "all Fs are Gs" is analytic, while holding fixed the antecedent meaning of „Fs‟ and „Gs‟.40 This point can be illustrated by reductio. Suppose that I were permitted to stipulate that I was adding to my idiolect a term „kats‟ such that „kats‟ refers to cats, but also that „all kats wear hats‟ is analytic, while holding fixed the ordinary English meaning of the rest of my language. If it were successful, this stipulation would allow me to truly make the claim that „all kats wear hats‟. But this is absurd, since there are evidently 37 I am indebted to a reviewer for Oxford Studies for pressing me to clarify this concern. 39 On some views, we might be entitled to „risky concept introduction‟. On this view, such stipulation would be legitimate semantic practice, with the proviso that our attempted stipulation would fail, absent the existence of a vindicating necessary connection in the world. Thanks to David Enoch for discussion of this idea. 40 There are at least two sorts of views on which it may be fair to say that we can stipulate such connections. On one such view, we sever the analyticity-truth link, so that it might be analytic but false that all Fs are Gs. Crucially, on this sort of view, the fact that such a connection was analytic would be no guide to whether it was necessary. Such a view would thus be no help in explaining (rather than, perhaps, debunking) the holding of the relevant necessary connection. On another view, metaphysically unconstrained analyticities might be enough to underwrite „metaphysically lightweight‟ necessities (compare Chalmers 2009: 95). However, such a „lightweight‟ approach to claims about the metaphysics of ethics is best understood in this context as suggesting a variant of quietist realism. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 18 cats that do not wear hats. This example suggests a constraint: given an allegedly analytic connection, there needs to be something in the metaphysics that can explain why this connection is necessary.41 Recall a point briefly made in §3: the reductive naturalist has exactly such an explanation. On her view, there is a necessary connection between ethical and base properties trivially, because the ethical properties are base properties. The crucial point is that stating the buck-passing view (if interpreted simply as a view about concepts) provides the non-naturalist with no analogous metaphysical story.42 The lesson of the above cases is that it is very attractive to seek to offer a metaphysical explanation of the connection between base and ethical properties. However, straightforward metaphysical suggestions on behalf of the non-naturalist make little progress. For example, in part of his response to the supervenience problem, Russ ShaferLandau suggests that: "We explain the ban on mixed worlds by claiming that a duly specified set of non-moral properties metaphysically must give rise to a certain moral property" (2003: 85). If intended to undercut the bruteness of the necessary connection between these types of properties,43 this proposal is clearly inadequate: to say that certain base properties must give rise to the ethical properties is to state the necessary connection to be explained, not to explain it. A more sophisticated variant of this strategy may appear more promising.45 Suppose that one was attracted to an essentialist metaphysics on which the way to explicate properties is to offer a real definition that states their essence. Such a view invites the hypothesis that the necessary connection might be explained by such essential facts. Consider a simple attempt to implement this idea with a conjunctive real definition: Being a reason =def having a distinctive justifying role R, and being realized by base property B. I take it that an instance of this schema for a real definition, if correct, perhaps would explain the supervenience of the ethical on the base properties. However, it suffers from a 41 There might also be case where analyticities can latch onto contingent a priori truths like "I am here now." However, this model is not going to help the ethical realist. 42 My objection here is close to Ridge‟s line of argument in (2007: 342-3). For what I take to be a different diagnosis, compare Olson‟s (2009: §3) claim that Stratton-Lake and Hooker have fallen victim to what he dubs the „extensional fallacy‟. 43 Another (and perhaps more charitable) reading of Shafer-Landau in this passage would take him to be using the metaphysical necessitation appealed to here to explain the weak supervenience of the ethical, and to not even be attempting to address the deeper challenge as I have formulated it. 45 I am indebted to Ralph Wedgwood for pressing a version of this idea. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 19 problem that I will call bruteness revenge: it offers an explanation of one necessary connection only by covertly relying on a second brute necessary connection. To see the problem, notice that on this definition being a reason is a peculiar sort of conjunctive property: it is a conjunctive property one of whose conjuncts (having a distinctive justifying role R) only combines with the other. To see how odd this is, contrast another toy real definition of a complex property: Being a bachelor =def being adult, being unmarried, and being male. Notice that any one of the properties in the definiens can combine with others to form a perfectly good property: there is nothing metaphysically puzzling about adult married males, for example. By contrast, there is no property that is constituted by the conjunction of having distinctive justifying role R, and being realized by the promotion of suffering (for example). Rather, R can only possibly combine with one base property – B – to form the real definition of a property. The non-naturalist proponent of explanation via real definition thus explains one necessary connection (in this case, between being a reason and being realized by a certain base property B) only to discover that she is committed to another brute connection, this time between the natural and non-natural constituents of the essence of a normative property (in this case between B and having justifying role R). This is not a reply to BRUTE CONNECTION; it simply moves the objectionable explanatory bump in the carpet. If my discussion of these three cases is correct, we can draw a general moral from each. First, because the non-naturalist rejects deflationism about the metaphysics of ethics, she cannot happily appeal to an ethical explanation of supervenience. Second, it seems that appeals to conceptual connections are likewise explanatorily inert. This is because any such connection, if it is to help, must ultimately be underwritten by a necessary metaphysical connection, thus raising the question of whether the latter connection is brute. Finally, attempts to undercut BRUTE CONNECTION by adding extra metaphysical structure are vulnerable to what I have called bruteness revenge: in effect, they are in grave danger of simply moving the objectionable explanatory bump in the carpet. This arises in a particularly straightforward way on a simple real definition strategy, but the core logic of that case naturally extends to others. It would be difficult to show that no instance of this strategy could be successful, but I have been unable to find a promising way forward for the McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 20 non-naturalist here.46 In the absence of direct responses such as these to BRUTE CONNECTION, a non-naturalist might instead seek shelter in a helpful model or analogy. In the next section, I examine the most salient instance of this strategy. 5. Non-reductive physicalism as a model Two leading non-naturalists, Russ Shafer-Landau (2003) and Ralph Wedgwood (2007), have recently emphasized the continuities between their views and non-reductive physicalism in the philosophy of mind. In this section I consider whether such an analogy might provide a model for rebutting BRUTE CONNECTION. One general problem that faces philosophers both in metaethics and the philosophy of mind is that there is no uncontroversial way of characterizing dualism, monism, and reduction. Indeed these views are sometimes distinguished in ways that do not seem to reflect metaphysical differences at all.47 In what follows I will examine one influential and reasonably motivated characterization of non-reductive physicalism. Begin with the following (again: controversial) taxonomy in the philosophy of mind:48  To claim that every mental property is identical to some physical property is to be a reductive physicalist about the mental.  To claim that every mental property supervenes with metaphysical necessity on the physical,49 but that mental properties are non-identical to physical properties (for 46 There are many interesting approaches to this problem that, sadly, would overburden an already long paper. My favorite of these would seek to extend FitzPatrick‟s (2008) „standards-based view‟ to account for strong as well as weak supervenience, by adding extra assumptions about the explanatory power of abstract objects. While fascinating, this approach also appears to generate a bruteness revenge problem. 47 For example, the locus classicus for discussions of reduction is Nagel (1961), which takes reduction to be a relation between theories rather than property-types. This had led some, especially the Cornell Realists, to call themselves „non-reductive realists‟ in metaethics on the basis of worries about the extensiveness of possible theoretical vocabularies. In a helpful passage that flags the tension between the Nagelian and metaphysical conceptions, Boyd (1997: 114-5) claims that while "in some sense all natural phenomena are „reducible‟ to basic physical phenomena" (emphasis and scare quotes his), reduction in the classical (i.e. Nagelian) sense must be rejected. 48 While common, this taxonomy is stated especially clearly in Bennett (2008: 284-6). 49 Some non-reductivists would want to permit the possibility of non-physical realizers for mental properties. For such non-reductivists, the relevant physical supervenience claim must be restricted to worlds that lack such non-physical realizers, and also any non-physical „realization-defeating‟ properties, if such are possible. One way to do this would follow Jackson‟s suggestion that, for any world that contains only physical realizers, every „minimal physical duplicate‟ of that world (which duplicates exactly those physical properties and adds no further realizing properties), will also contain the same mental property instances as the duplicated world (compare his 1998: 12-13). I set aside important further worries with treating Jackson‟s proposal as a sufficient condition for physicalism. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 21 example, because they are multiply realizable), is to be a non-reductive physicalist about the mental.  To deny that the mental supervenes with metaphysical necessity on the physical is to be a dualist about mental and physical properties. The first thing to note about this taxonomy is that it appears to presuppose at least a local instance of Hume‟s dictum. Because of this, if we treat this taxonomy as an instance of a general metaphysical schema (as is usually intended), the ethical non-naturalist‟s commitment to ontological „dualism‟50 is simply inconsistent with accepting the metaphysically necessary supervenience of the ethical on the base properties. The strategy under consideration here concedes this presupposition, in order to see whether the view defended by ethical non-naturalists might in fact best be modeled on non-reductive physicalism, and not dualism. My discussion in this section will focus on two questions about this strategy. First, can the non-reductive physicalist provide an adequate answer to the supervenience problem? Second, can adopting this answer help the would-be ethical non-naturalist? On the taxonomy just sketched, non-reductive physicalists hold that physicalism is true, because on their view the mental supervenes with metaphysical necessity on the physical.51 They deny reduction, however, because they claim that mental properties are multiply realizable. The paradigm of a putatively non-reductive explanation of both multiple realizability and supervenience is functionalist.52 An (oversimplified) toy example will illustrate the central idea. If a system takes some cash as input and reliably gives a coke as an output, then, on a functional conception of coke machines, it is a coke machine. Functionalism can explain multiple realizability because this input-output relation could seemingly possibly be instantiated by a structure composed of mud brick, or plastic, or even, perhaps, by spooky supernatural stuff. Functionalism can also offer a plausible explanation of (a suitably restricted) supervenience thesis. Paradigmatic functional kinds like coke machines are causal 50 Of course, a non-naturalist would not strictly count as a dualist, if she believed in more than two fundamental kinds of things. 51 This supervenience claim will need to be restricted (as discussed in n. 49 above), if mental properties can be realized or blocked by non-physical properties. 52 I am setting aside a range of important controversy about non-reductive physicalism here. On the one hand, the very possibility of non-reductive physicalism has been repeatedly challenged, most famously by the many variants of Kim‟s (1993 and elsewhere) causal exclusion argument. The idea of multiple realizability has been less frequently challenged, but for an important exception, see Shapiro (2000). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 22 functional kinds. Since certain physical states (perhaps together with physical laws) essentially necessitate certain causal properties, there is no mystery about the supervenience of essentially causal kinds on physical properties. Why does the existence of a certain configuration of plastic, steel, and coke entail the existence of a coke machine? Because the total physical nature of this configuration just entails that if one puts a dollar into it, one reliably gets a coke in return. This functional fact, in turn just is what it is to instantiate the functional kind coke machine. As Nadeem Hussain has argued, however, the smoothness of this sort of account of necessitation depends upon the fact just noted: that the functions appealed to by the standard non-reductive physicalist are causal functions.53 In the terms introduced in §1 above, the causal nature of functional properties arguably makes them metaphysically continuous with physical properties, thus violating one of the central conditions for nonnatural properties suggested in §1.54 This would not be much of a worry if the discontinuity condition were an arbitrary feature of my theoretical characterization of non-naturalism. However, it is not. Rather, it can be motivated by one of the core commitments of nonnaturalism. This is what David Enoch pithily called the „just too different‟ intuition (2007: 44 n.47): the claim that the natural and normative are radically different sorts of things. Derek Parfit makes a version of the same intuitive claim, when he says that the natural and the normative are like rivers and sonnets, in that we can just tell that they are radically different (2011, 324). This intuition is arguably at the heart of many non-naturalists‟ view that naturalistic realism is not merely incorrect, but a non-starter. (It leads Parfit, for example, to wonder if naturalists are even trying to understand the same property that he is interested in).55 It is striking, then, that we do not have this sort of reaction to paradigm cases of non-reduction via multiple realizability. I do not think that a coke machine is „just too 53 Hussain (ms.). Hussain cites Kim (2006: 120), which defines functional properties in terms of causal roles. 54 Some non-reductive physicalists reject causal functionalism about the mental, especially the phenomenal. However, the crucial question is whether such non-functionalist views can provide a good explanation of the relevant necessary connections. In the absence of such an explanation, they may be unable to resist the sort of intuitive doubts about the (metaphysical grade) supervenience of the phenomenal that lead Chalmers (1996) to dualism. It is thus unclear how appeal to these views as a model could help to undercut BRUTE CONNECTION. 55 It should be said that not everyone who is typically classed as a non-naturalist is gripped by this intuition. For example, in conversation Ralph Wedgwood has suggested that he is unmoved by it. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 23 different‟ from the arrangement of plastic, steel and coke that constitute it to count as a physical thing. I just think that there are other physical (and perhaps non-physical) systems that would also be coke machines. In other words, a non-reductive metaphysics appears insufficient to account for the contrast that the ethical non-naturalist is committed to pressing. One might think that the residual contrast could be explained in nonmetaphysical terms, for example in terms of features of the semantics or epistemology of the ethical. This, however, is exactly what naturalists and expressivists have typically argued against the non-naturalist: that the materials that the non-naturalist takes to motivate a metaphysical difference can be explained away in other terms. It is thus hard to see how would-be non-naturalists could rest easy with such explanations. Other clear models of non-brute necessary connections between properties also seem to be between properties that are relevantly continuous. This seems true, for example, of determinates and determinables. Intuitively, it is necessarily true that anything that is crimson is red, for example. However, being red and being crimson are surely both going to get the same general treatment by the philosophy of color, and if they did not, this would cast doubt on my casual positing of a necessary connection between them. What we seem to need as friendly analogy for the ethical properties is an explicable necessary connection between a pair of properties that are strongly metaphysically discontinuous. I have argued that non-reductive physicalism is no help here, and other candidates appear difficult to produce. The discussion in this section thus suggests contrasting answers to our two central questions. The functionalist non-reductive physicalist may be able to offer an acceptable explanation of the (alleged) metaphysically necessary connection between physical and mental properties. However, the structure of this explanation depends upon features of the non-reductive physicalist‟s view that appear incompatible with core non-naturalist commitments. It is thus very difficult to see how this analogy can help the non-naturalist address her version of this problem. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 24 6. Resisting the MODEST HUMEAN thesis I have just argued that the seemingly most inviting ways of challenging BRUTE CONNECTION (the idea that the non-naturalist must take the supervenience of the ethical to be a brute fact), face serious difficulties. In light of this, the non-naturalist might consider instead trying to undercut the remaining premise in my central argument: the MODEST HUMEAN thesis that commitment to such brute necessities counts significantly against a view. I consider two versions of this strategy: the first seeks to undercut MODEST HUMEAN by appeal to companions in guilt, and the other attempts to raise methodological questions about the intuitive case for the thesis. Some philosophers have pressed more radical versions of the Humean idea, for example claiming that necessary coextension entails reduction or identity.56 Unsurprisingly, many non-naturalists have taken up arms against this existential threat to their views.57 However, it should be clear that seeking to undercut this entailment (especially via argument from cases such as the distinctness of necessarily coextensive properties like triangularity and trilaterality, which are surely metaphysically continuous) does nothing to impugn MODEST HUMEAN. The central argument of this paper does not involve the claim that the supervenience burden entails that non-naturalism is incoherent. Rather, I am inclined to think that the ubiquity of philosophical assumptions that necessary connections entail reduction or at least monism (as in the characterization of non-reductive physicalism in the previous section) provides excellent indirect evidence for the more modest claim that one takes on an intuitively powerful explanatory burden in accepting brute necessary connections between distinct properties. Shafer-Landau seeks to undercut the thought at the heart of MODEST HUMEAN by appealling to the unavoidability of positing brute facts. He begins by correctly observing that any line of metaphysical explanation must end with some brute facts. For example, he suggests that once we identify the most fundamental laws of physics, there is no sense in asking the realist about physics what makes those laws true (2003: 97). In assessing this 56 For defense of the link between necessary coextension and reduction, see for example Kim (1993: 151). For the view that the necessary coextension must be knowable a priori in order to suffice for reduction, see Chalmers and Jackson (2001). 57 For example, see Majors (2005: §3), Shafer-Landau (2003: 89-91), Suikkanen (2010), and Wedgwood (2007: 136-147). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 25 response, it is crucial to distinguish the supervenience burden from the general complaint that non-naturalism is ontologically profligate. Shafer-Landau‟s point may serve as a useful corrective against the latter complaint, reminding us that positing novel classes of properties is sometimes indispensible. (Be careful lest your zeal to trim „Plato‟s beard‟ leads you to amputate part of what there is!) However, this line of argument fails to address the distinctive burden posed by supervenience. This burden stems not from the non-naturalist‟s positing extra properties, but from their need to posit brute necessary connections between distinct properties.58 Unlike positing brute properties, it is highly controversial whether this is ever necessary in metaphysics, so there is no clear argument here from inevitability. One might seek to develop the objection by focusing on the fact that it involves appeal to an analogy with laws of nature, not mere brute properties. Consider an example: what is the best explanation for the (approximate) truth of general relativity? Realists about the laws think that it looks bad to suggest that all of the particular contingent facts in our actual world – past and future – just happen to miraculously line up in a way that satisfies this theory. The alternative is seemingly to posit a further metaphysical element – a law of nature – that explains this regularity.59 Such a law is exactly a brute necessity. Such an example may seem to suggest that brute necessary connections are not so bad. Indeed, they can seemingly be more explanatory than brute contingencies. There are two difficulties with this analogy. On the one hand, there is the modality of this necessity: if it is nomic rather than metaphysical (as is usually assumed about the laws of nature), the analogy may lose much of its force. More importantly, the alternative in realist metaethics is not to take the ethical properties of each action to be a distinct contingency: this really would be a remarkably odd view. Rather, it is to offer a naturalistic realist account of the nature of the ethical properties that entails the supervenience relation. To repeat: on such a view, the metaphysics of supervenience is not puzzling at all. 58 Shafer-Landau also claims parity between the non-naturalist‟s explanatory burden in positing a necessary connection between distinct properties, and the identity naturalist‟s explanatory burden in positing identities between ethical properties and certain natural properties (2003: 96). This claim must, I think, rest on conflating metaphysical with pragmatic explanation. Among metaphysical claims, identity claims surely require the least explanation. "Why is X identical to X?" is hard to even hear as a literal question. 59 Compare Lowe (2002: 380). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 26 Other companions in guilt are possible, but none are uncontroversial. One general difficulty with appeals to such companions can be illustrated by considering mathematical Platonism, which is probably the strongest candidate. Suppose that we grant that commitment to mathematical Platonism requires belief in metaphysically brute necessities (which seems true). And suppose that we grant further that mathematical Platonism is nonetheless on balance the most attractive view in the philosophy of mathematics (which is far from obvious). Even these generous suppositions fail completely to show that commitment to brute necessities does not count significantly against a view. All that they would show is that the commitments that derive from a domain that is arguably our paradigm of collective epistemic success may be sufficient to overcome this burden. What would, perhaps, undercut the MODEST HUMEAN thesis is a case for the ubiquity of brute necessities across a range of domains. However, it is plausible that such a case could only be made within an unusually inflationary ontology. It is notable that, for the proponent of such an ontology, ethical non-naturalism would not be a distinctively motivated view, but would rather threaten to be a trivial consequence of the failure of anything in metaphysics to be exhaustively explained in terms of an elegant ontological base. This seems to me contrary to the spirit of much contemporary non-naturalist argument. The non-naturalist might seek to debunk, rather than combat, the intuitive force of the intuitions that ground the MODEST HUMEAN thesis. However, this option is at least somewhat methodologically awkward.60 This is because the case for the force of this thesis rests fundamentally on powerful methodological intuitions in metaphysics. What MODEST HUMEAN denies is that we are permitted, in metaphysical theory construction, to embrace brute necessary connections whenever they appear to be otherwise convenient posits. This is close to simply being a characteristic mark of taking the metaphysical project seriously. Attacking this powerful intuitive thesis will be awkward for many non-naturalists, because non-naturalism is almost always grounded in an extremely intuition-friendly methodology. 60 This point is perhaps best illustrated by Wedgwood‟s (2007: 202-212) forceful exposition of the burden within the context of an otherwise non-naturalism-friendly framework. Wedgwood then (2007: 212-220) attempts an inventive solution to this burden. For critical discussion of this attempted solution, see my (2009) and Schmitt and Schroeder (forthcoming). McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 27 This is not, of course, to say that such a debunking argument is inconceivable.61 However, it is not at all clear what general grounds an intuition-friendly philosopher might have for suspicion in a thesis whose tacit acceptance appears to underlie much of contemporary metaphysics. The modesty of MODEST HUMEAN may appear to invite a final non-naturalist response to this argument: sanguine acceptance, modulo some „dickering about the price‟. A crucial difference between this thesis and Hume‟s dictum itself, after all, is that MODEST HUMEAN permits the coherence of non-naturalism. Even if the whole argument succeeds, it only concludes that supervenience „counts significantly against‟ the view. But it is quite difficult to see how to argue convincingly about the weight of this consideration. It is thus open to the non-naturalist to simply grant the existence of a burden, but deny that it is particularly weighty.62 I take this to be a misguided response, but I also take arguing this point to be a tortured endeavor. The only compelling way to proceed, it seems to me, would be to move from domain to domain in metaphysics, considering the explanatory burdens and puzzles that one might escape by positing analogous necessary connections, and arguing repeatedly that even such philosophical riches are not worth the methodological price of such posits. I conjecture (and it is only that) that anyone unmoved by such a tour would find themselves generally amenable to a highly inflationary metaphysics. I thus strongly suspect that this response would in effect collapse into the view mentioned above, on which ethical non-naturalism ceased to be an interestingly locally motivated view after all. Conclusions Contrary to the idea just sketched, I take ethical non-naturalism to be powerfully motivated: of all metaethical views it perhaps most deeply reflects compelling intuitively commitments to the objectivity, robustness, and distinctiveness of ethical facts and properties. However, I have argued in this paper that the non-naturalist cannot easily escape a carefully formulated metaphysical version of the supervenience burden that it has 61 Non-naturalists can, of course, potentially debunk intuitions: for an important model, see Huemer (2008). 62 I am indebted to David Enoch for forcefully pressing this response. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 28 traditionally been understood to face. As the preceding sections of the paper have been concerned to canvass objections to the argument, permit me to briefly restate the central positive argument. This argument appeals to three core claims: SUPERVENIENCE No metaphysically possible world that is identical to a second world in all base respects can be different from the second world in its ethical respects. BRUTE CONNECTION The non-naturalist must take the supervenience of the ethical properties on the base properties to involve a brute necessary connection between discontinuous properties MODEST HUMEAN Commitment to brute necessary connections between discontinuous properties counts significantly against a view Having characterized non-naturalism in §1, I argued in §2 that non-naturalist ethical realists (like other realists) have excellent reasons to accept SUPERVENIENCE. I also noted that even if these reasons were defeated, they would have reason to accept a related supervenience thesis that would present them with very similar issues. In §3, I argued that we have excellent reasons to accept the MODEST HUMEAN thesis, and offered some motivation for accepting BRUTE CONNECTION. In §§4-5, I canvassed a range of attempts to resist BRUTE CONNECTION, and argued that it is extremely difficult to rebut. Finally, in §6, I argued that there are no easy roads to undercutting MODEST HUMEAN. Like most philosophical arguments, this one is open to question at many points. Part of my ambition in setting out the central case as clearly as possible is the hope that others will find compelling ways to rebut one of these premises that I have not found. Because I take non-naturalism to have many attractive features, I would take this to be a happy result. Further, even if sound, this argument only entails that there is a substantial objection to non-naturalism. Its soundness is thus compatible with non-naturalism being developed so as to be otherwise so attractive that this burden is outweighed. In advance of such happy surprises, however, when the supervenience problem for non-naturalism is refined in the way expounded in this paper, it remains one of the most difficult challenges facing the view.63 63 I am deeply indebted to David Plunkett, David Enoch, Bill FitzPatrick, Frank Jackson, Matt Bedke, Dan Baras, and two anonymous reviewers for Oxford Studies in Metaethics for comments on drafts of this paper. I am also grateful to audiences at ANU, the University of Sydney, the Madison Metaethics Workshop, the University of Delaware, the University of Tennessee Knoxville, Washington University St. Louis, and Virginia Tech for wide-ranging and enlightening discussion. Finally, thanks to Jamie Dreier, Daniel Nolan, Mike Titelbaum, and Dave Chalmers for helpful discussion of related issues. McPherson Ethical Non-naturalism and the Metaphysics of Supervenience 29 Works Cited Adams, Robert. (1999) Finite and Infinite Goods. (Oxford: Oxford University Press). Audi, Robert. 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