1 Introduction

Naturalism is one of the main paradigms of contemporary philosophy. While the term “naturalism” is used in many ways, the two main forms of naturalism are ontological naturalism and methodological naturalism (cf. Papineau 2015). Ontological naturalism is the thesis that only those things fundamentally or truly exist which are countenanced by the theories of the natural sciences. The most commonly accepted sub-species of ontological naturalism is physicalism, according to which only those things fundamentally or truly exist which are countenanced of the theories of a future-ideal state of physics, all else having to be suitably related to such entities through supervenience or reduction, or having to be eliminated altogether. Methodological naturalism, on the other hand, states that philosophy is “continuous with science” (Quine 1960, p. 209). There are at least a dozen ways of spelling out the specifics of methodological naturalism, and it is difficult to adjudicate which specification of methodological naturalism is authoritative. But one essential point of a commitment to methodological naturalism is that the natural-scientific method (or methods) figure as a yardstick for philosophical research.Footnote 1

Some proponents of either form of naturalism have been acutely aware of some of its problems. The first problem pertains to methodological naturalism, namely that it is incoherent. Methodological naturalism articulates a basic principle, i.e. that philosophy should be aligned with the natural sciences in a specific way. Yet, methodological naturalism itself cannot be justified by that basic principle. The second problem pertains to ontological naturalism, namely Hempel’s dilemma which states that ontological naturalism is either a false thesis (since current physics cannot account for all of reality) or a trivial thesis (if a future-ideal physics is promised to account for all of reality).Footnote 2

The interesting strategy that different proponents of either form of naturalism have proposed, seemingly independently from another, address these two different problems. This strategy consists in reformulating ontological naturalism and methodological naturalism as an attitude,Footnote 3 or research program,Footnote 4 or as a project.Footnote 5 While there are differences between these three contenders,Footnote 6 what unites these two conceptions that they present the same strategy of naturalists to defend against Hempel’s dilemma.Footnote 7 It is common to all three of them, for example, that they redefine either ontological or methodological naturalism as something non-truth-evaluable. For the sake of simplicity, I shall henceforth refer to either of these as “attitude accounts”.

In this paper I aim to show that attitude accounts remain unsuccessful because they incur yet another dilemma: naturalism as an attitude either collapses into a truth-evaluable thesis again, or naturalism as an attitude is essentially a-rational. To this end, I shall first go into more detail on the problems of the two different forms of naturalism, and then tease out the dilemma. Lastly, I will consider what the best course of action for naturalism might be here, and suggest that one interesting option may be to conceive of naturalism as a worldview which I will construe as a more extreme form of the attitude account, one which fully embraces its a-rational status.

Some terminological clarifications are in order. I use “naturalism” as the generic term under which both methodological naturalism and ontological naturalism are specifications. Furthermore, for the sake of symmetry, I use “ontological naturalism” and “physicalism” interchangeably. Similarly, I use “attitude” as a generic term under which the terms “research program”, “disposition”, or “stance” may be subsumed; while these latter terms refer to differing notions, they are sufficiently similar for the purposes of this investigation, insofar as none of them are truth-evaluable.

2 Two Dilemmas for Two Naturalisms: Hempel’s Dilemma and the Coherence Dilemma

There are two distinct problems for methodological naturalism and ontological naturalism respectively: Hempel’s dilemma pertaining to ontological naturalism and a looming incoherence charge against methodological naturalism. I shall briefly offer a construal of both of these problems and then demonstrate how both naturalisms resort to the same strategy, namely reformulating ontological naturalism and methodological naturalism as an attitude rather than a thesis.

First, Hempel’s dilemma (Hempel 1969) states that ontological naturalism is either obviously false or trivial. Ontological naturalism is false if current physics is taken as a standard for a naturalistic ontology. This is because current physical science does not include and would be unable to account for non-physical properties including the mind and normativity. On the other hand, ontological naturalism is trivially true (and hence uninteresting) if the ontological naturalist merely promises that a future-ideal physics will account for everything, including normativity and the mind.Footnote 8 It is trivial because the physical would obviously have to expand its domain in order to account for all phenomena even if it means including mental or normative ones.

Neither horn of the dilemma is something an ontological naturalist could be content with. Hence, Hempel’s dilemma has constituted a reason for major concern among physicalists ever since it was first formulated. Alyssa Ney’s widely received solution to this dilemma is to not understand ontological naturalism as a thesis (as it has been traditionally viewed), but rather as a stance or attitude which includes forming “one’s ontology completely and solely according to what physics says exists” (Ney 2009, p. 9). Physicalism as an attitude is not truth-evaluable, but rather a commitment to a physicalist “oath”: “I hereby swear to go in my ontology everywhere and only where physics leads me” (Ney 2009, p. 5). Taking an oath, which can be qualified as an illucotionary speech act, cannot be true or false. One can fail to uphold the oath, but the content of the oath itself is thereby made neither true nor false. By not being truth-evaluable, ontological naturalism avoids both horns of the dilemma. On the one hand, it avoids triviality because it retains a commitment to current physics, not a future-ideal expansion of physics, insofar as the Ney’s oath simply names “physics”. On the other hand, it avoids being obviously false because it is not truth-evaluable: tautologically, statements which are not truth-evaluable obviously cannot be false. Ney views this physicalist attitude as supported by empirical evidence since “explanatory success of physics supports the attitude of taking physics as a guide to one’s ontological commitments” (Ney 2009, p. 10). And she adds: “Insofar as physics provides empirically supported claims about the internal mechanisms of what we experience, we are […] justified in forming beliefs about what is fundamental using its deliverances”. This justification promotes “physicalism beyond the status of a mere dogma” (Ney 2009, p. 11), as it were.Footnote 9 Ney’s account of ontological naturalism as an attitude is to date one of the most well-developed expressions of this idea which seems to capture the often tacit convictions of many naturalists.

The second problem, pertaining to methodological naturalism, is a threat to its coherence. To get this looming incoherence into view, it is helpful to look at a similar case of in the history of philosophy, namely (incidentally again) Hempel’s empiricist criterion of meaning. The empirical criterion of meaning “qualifies a sentence as cognitively meaningful if its non-logical constituents refer […] to observables” (Hempel 1950, p. 58). This leaves the idea that a sentence is meaningful if it is suitably connected to empirical observations. This would render metaphysical statements (of the kind positivists like Carnap and others loathed) meaningless because they would, by definition, not be related to empirical observations in a way the empiricist countenances. The main problem is that the empiricist criterion, if true, is itself without meaning. This is trivially so because the empiricist criterion does not involve, or suitably relate to, empirical observations. Once the criterion is formulated, it would be without meaning, rendering it incoherent: if the empirical criterion of meaning does have meaning, it thereby does not have meaning. The empiricist criterion is thus incoherent because it cannot meet the very standard set by itself.Footnote 10

Taking the incoherence of the empiricist criterion of meaning as a blueprint, something very similar besets methodological naturalism: the methodological thesis sets a standard for justification which it itself cannot meet. The methodological thesis states that philosophy should align itself with the natural sciences regarding its treatment of those philosophical problems which remain once all other problems have been deferred to the natural sciences. In this sense, whether or not a certain philosophical approach, statement, or theory is justified hinges upon whether or not it is properly aligned with some kind of natural-scientific methodology in the sense that that philosophical statement or theorem can at least be countenanced from a natural-scientific standpoint.

This looming incoherence has been noted by a number of proponents who actually endorse methodological naturalism. In his World without Design, Michael Rea, himself a card-carrying naturalist, sees that methodological naturalism formulated as a thesis as “self-defeating or otherwise unacceptable” (Rea 2002, p. 60). Rather than disavowing naturalism, Rea aims to reformulate methodological naturalism as an attitude:

“neither [methodological, TJS] naturalism nor any alleged version thereof can be expressed as a substantive philosophical thesis that is neither at the mercy of science nor self-defeating, vacuous, or otherwise naturalistically unacceptable. If I am right, then we have only two options: either we reject naturalism and its alleged varieties as severely internally defective, or we draw the conclusion that naturalism is not a substantive philosophical position. Charity requires us to take the latter option.” (Rea 2002, p. 53f.)

Rea substantiates his preferred option by characterizing naturalism as a research program. Research programs in turn are characterized as a “set of methodological dispositions – a way of conducting inquiry” (Rea 2002, p. 66; an idea he traces back to Roy Wood Sellars).Footnote 11 Methodological dispositions, in turn, are dispositions which “our cognitive faculties [trust] as sources of evidence” (Rea 2002, p. 1), e.g. our disposition to trust mathematical or logical statements, as well as the deliverances of our senses under standard conditions. And in the case of naturalism as a research program, part of that set of methodological dispositions is the disposition to align one’s convictions (philosophical and otherwise) with the results of the natural sciences.

Similar as to how Hempel’s dilemma poses an issue for ontological naturalism, Rea sees methodological naturalism pressured by another dilemma, namely that methodological naturalism is either “internally defective” or not a “substantive philosophical position” at all. And Rea has no problem with methodological naturalism to be impaled on the second horn, i.e. concluding that methodological naturalism is not a position, or in the terminology so far, not a thesis. Rea thinks because naturalism, formulated as a thesis, has to be incoherent, unjustifiable or “epistemically circular” (in his terminology), it is uncharitable to understand naturalism as a thesis. For the sake of charity, we therefore have to understand it as an attitude. This is because once naturalism is viewed as an attitude it is not truth-evaluable, and hence not self-defeating in the same manner that Hempel’s empiricist criterion of meaning was. Rea’s notion of research programs is obviously different from, say, Ney’s notion of attitudes. Yet they are the same in a crucial respect: Rea circumvents giving up on methodological naturalism (admitting its “internal defectiveness”) by introducing the same strategy as Ney did in relation to ontological naturalism: reformulating naturalism as an attitude. (For the sake of conciseness, the term “attitude” is being kept as a catch-all under which Rea’s “disposition” can be subsumed. This is because neither are truth-evaluable which is the deciding factor in the current context.)

Summarizing the progress so far, both ontological naturalism and methodological naturalism face their own specific dilemma: Hempel’s dilemma for ontological naturalism and the coherence dilemma for methodological naturalism. And arguably, methodological naturalism and ontological naturalism can be endorsed separately from one another. It is therefore interesting that representatives of either kind of naturalism utilize the same strategy to address their respective dilemma, namely reconceiving (ontological and methodological) naturalism as an attitude (rather than a thesis).

3 A Third Dilemma for Naturalism as an Attitude

Reconceiving different forms of naturalism as an attitude (rather than a thesis) seems to be at least prima facie a viable strategy to avoid Hempel’s dilemma and the coherence dilemma. Considering the long duration in which versions of naturalism have dominated analytic philosophy, the and Dove’s strategy to reconceive of naturalism as an attitude is fairly recent. Yet, some authors have pre-emptively defended the strategy to reformulate kinds of naturalism as attitudes in different ways.Footnote 12

This section is dedicated to raise a further, not sufficiently addressed worry regarding this rephrasing strategy. This strategy faces its own dilemma: naturalism as an attitude either collapses into a thesis again or is potentially a-rational. Both horns are genuinely undesirable for the naturalist: the collapse from attitude to thesis would render the two naturalisms vulnerable to their initial problems which motivated to reformulation as a stance in the first place. And naturalists will generally want to avoid holding onto beliefs which are a-rational. Note that the following dilemma pertains to both methodological naturalism and ontological naturalism equally insofar as both have been defended as attitudes.

According to the first horn of this third dilemma, naturalism is unstable as an attitude. This is because the content of an attitude can simply be reformulated as a thesis. But once the content of naturalism as an attitude has been reformulated as a thesis, naturalism itself becomes susceptible again to either of the preceding dilemmas, i.e. Hempel’s dilemma or the coherence dilemma. And then, the naturalist would be back where they started. This has been noted by Rik peels, albeit in a context which focuses on scientism: naturalism “can be translated into a thesis, such as the thesis that we should have that affection, attitude, or stance, or the thesis that it is permissible to have that affection, attitude, or stance” (Peels 2017, p. 1f.). In other words, a non-truth evaluable attitude can trivially be reformulated as a truth-evaluable statement. When prompted to explicate the content of one’s naturalistic stance, that content can be reformulated into a truth-evaluable statement. And the naturalist would be prompted to give a rational justification for the reformulated attitude, on pain of not being rational.

This can be applied to the concrete approaches that came up in the preceding section, i.e. Ney’s and Rea’s respective strategies.

Firstly, consider again Ney’s attitudinal approach which she expresses as a commitment to the physicalist oath:

Oathattitude: “I hereby swear to go in my ontology everywhere and only where physics leads me” (Ney 2009, p. 5).

According to Peels’ challenge, the oath can simply be reformulated into a truth-evaluable statement:

Oathtruth: It is justified to construe all of one’s ontological commitments in terms of the results of physics.

While this is certainly not the only possible way to phrase the conceptual contents in Ney’s oath, it seems to be a viable expression of her reasoning, given the fact that she seems to prefer the Quinean terminology of “ontological commitments” a total of 38 times throughout making her case. Ney does make the case that ontological naturalism is supported by empirical evidence (Ney 2009, pp. 4 and 10) which makes it the preferable version of ontological naturalism, elevating it “beyond the status of a mere dogma” (Ney 2009, p. 11). While the truth-conditions of the Oathtruth are difficult to determine, the statement must be truth-evaluable, thereby making Hempel’s dilemma applicable again.

In a similar fashion, phrasings of naturalism as a research project analysable as a set of methodological dispositions can be rephrased. When questioned on the content or reasoning of dispositions guiding their action and belief, a card-carrying Rea-style naturalist (most likely another professional philosopher) might express their belief in the following manner:

“I align my philosophical beliefs and research with the deliverances of the natural sciences because philosophy is continuous with science.”

Again, this is only one possible formulation. A Rea-style naturalist might also just justify their disposition by claiming that it is simply reasonable to do so. When further pressed, the Rea-style naturalist would perhaps recount several of the usual arguments for the conviction that following the natural sciences is reasonable. For example, Ney suggests that physicalism conceived as an attitude is preferable because it allows physicalism to receive empirical support, such that the physicalist “oath” can be vindicated by looking to empirical evidence (Ney 2008, p. 11). Elpidorou and Dove (2018, p. 18), too, suggest that their physicalism, as an empirically informed research program, is an expression of “optimism” and a “promise”. Their justification for this optimism is that we have good reason to assume, as it were, that the research progress concerning consciousness of the last twenty years has wrought more knowledge in that area than the whole rest of human history combined. It is this progress, they seem to suggest, that allows for optimism that physicalism as an attitude can be vindicated ex post in the future. Specifically tailored to methodological naturalism, Ronald Giere suggested that commitment “to the method [of science, TJS] can be sufficiently justified by appealing to past successes at finding naturalistic explanations […]” (Giere 2000, p. 214f.). Similarly, Ladyman and Ross insist, responding to Lowe’s version of the incoherence charge, that “[…] even if naturalism depends on metaphysical assumptions, the naturalist can argue that the metaphysical assumptions in question are vindicated by the success of science” (Ladyman and Ross 2007, p. 7). The most forceful expression of this idea is perhaps found in Rosenberg: “The reason we trust physics to be scientism’s metaphysics is its track record of fantastically powerful explanation, prediction, and technological application. If what physics says about reality doesn’t go, that track record would be a totally inexplicable mystery or coincidence” (Rosenberg 2014, p. 19).Footnote 13

Regardless of the merit of such arguments, the initial statement justifying their naturalist disposition is truth-evaluable. And taking account that this is a variation of methodological naturalism, the threat of the coherence dilemma or “epistemic circularity” (in Rea’s own terms) would apply again to this statement. In both instances, naturalism as an attitude seems to turn back again into naturalism as a thesis. It seems therefore, that the naturalist would have to demonstrate somehow that Peel’s challenge – the transposition from attitude to thesis – is somehow illegitimate.

The second horn of the dilemma arises if the naturalist somehow were to insist or demonstrate that naturalism can only be formulated as an attitude (thereby resisting the first horn in some way). The naturalist would most likely have to do this by resisting calls to justify the naturalistic attitude or disposition in the first place. For if the naturalist does not even utter the contents of the attitude or disposition in question, their expression and justification cannot be used in a reformulation as a thesis, which would put a stop to the regression from naturalism as an attitude to naturalism as a thesis.

While this would at first seem to vindicate naturalism as an attitude, this would come perhaps at a higher price. For this strategy would render naturalism as such a-rational as mere belief or mere faith. A commitment to naturalism as an attitude would then be a-rational in the full neutral sense of the word: naturalism as an attitude would not be inaptly or insufficiently justified, it would rather not be rationally justifiable at all, fully outside the philosophical game of giving and asking for reasons.

To clarify this point, two kinds of attitudes (or dispositions) need to be distinguished. On the one hand, there are those attitudes which are not in need of rational justification; and there are those attitudes which are in need of rational justification. The first kind of attitudes pertains to preferences and matters of taste. For example, someone’s preference for vanilla ice cream (opposed to strawberry ice cream) does not have to be rationally justified. Nor is someone’s favourite colour being blue a matter for rational justification. These attitudes may, to varying degrees, depend one one’s taste and include something like faultless disagreement.

The second kind of attitude pertains to more serious matters. For example, one’s attitude towards political matters (like the death penalty, child marriage, or private gun ownership) may be in need of justification. Topics, questions, and assertions in philosophical practice themselves are of the same kind (even if they usually do not have stakes as high as matters of death penalty or child marriage). There is no faultless disagreement to be had here. In such cases, asking for justification is itself justified in a way that it is not in matters of preferences which are merely a matter of taste. A fortiori, ontological and methodological naturalism, being distinctly philosophical matters, are in need of justification; proponents are at least prima facie justified in asking for reasons for believing a variation of methodological or ontological naturalism or holding a corresponding attitude, disposition, or intuition. Hence, a principled refusal to provide justification for methodological or ontological naturalism (in any of its forms) would render such commitment a-rational. By their very nature, philosophical beliefs cannot be a-rational if they are to be genuinely philosophical.Footnote 14 Furthermore, holding naturalism as an attitude in conjunction with a refusal for further justification would then be in tension with the naturalist’s preference for intellectual virtues governing the scientific process, among which rational justification is chief.

The first horn of this third dilemma states that ontological or methodological naturalism as an attitude can be reformulated as a truth-evaluable thesis, thereby making it vulnerable again to Hempel’s dilemma or the coherence dilemma respectively. This could, in principle, be resisted by disavowing or rejecting rational justifications of naturalism as a stance by simply keeping quiet. This triggers, however, the second horn of the dilemma according to which naturalism as a stance is a philosophical matter about which further justifications can be demanded, thereby rendering a rejection of justification of naturalism as a stance a-rational which would be genuinely unacceptable for any philosopher.

4 In Lieu of a Conclusion: Naturalism as a Worldview

So far, I have argued that ontological naturalism and methodological naturalism face a third dilemma if they are to be reconceived as an attitude (after they have faced Hempel’s dilemma and the coherence dilemma in their form as theses respectively). The first horn of this third dilemma states that naturalism as an attitude is unstable because the content of an attitude (or oath or disposition) can simply be rephrased as a thesis again. The second horn states that resisting further demands for justification, naturalism as an attitude is threatened to become a-rational, something which is unsatisfactory in the context of philosophical debates.

What is then the best option to proceed for a friend of naturalism? One of the most promising courses of action would be to allow naturalism to become a thesis again. Naturalism has many strong proponents, putting it into a good position to perhaps mount a decisive defence against both Hempel’s dilemma and the coherence dilemma. We might just want to leave a solution to Hempel’s dilemma up to time and the collective brainpower of swathes of naturalists developing and defending their positions.

There is, on the other hand, a route less commonly travelled, namely embracing naturalism not only as an attitude, but rather as a worldview. In other words, fully embracing the a-rational character of naturalism as an attitude can be taken to a more extreme form which lies in endorsing naturalism as a Weltanschauung, image, worldview, or even ideology. In fact, there is a tradition of engagement with naturalism (or materialism, physicalism) which from the outset conceives of it as a worldview. That is, as something whose propositional content can be expressed in statements, but whose overall status is different. This sense is present in metaphysical reflections prior to the advent of analytic metaphysics, most notably in Karl Jaspers and Wilhelm Dilthey. According to Jaspers’s theory of worldimages (Weltbilder), worldimages fixate a part of whole reality and take that part to be the whole (Jaspers 1925, p. 123f, cf. also 129). Ontological naturalism (“materialism” in older diction) as a worldimage fixates on the natural (“material”) aspect of the world and posits that there is nothing to the world beyond that aspect. Indeed, naturalists would not even call it a mere “aspect”, but rather either the “only” or the “most fundamental” thing there is. According to Dilthey, worldimages offer a systematisation and structuring of the whole of human experience into a set of problems and solutions. In the case of naturalism, this is mirrored in the multitude of developments for naturalistic accounts of phenomena pertaining to all kinds of human experience (e.g. ethics, aesthetics, sociality; Dilthey 1960, pp. 82, 849).

While not as exhaustively as found in the oeuvres of Jaspers and Dilthey, some analytic metaphysicians have been apprehensive of this peculiar status of naturalism. Most notably, Wilfrid Sellars’s developed his own grand holistic naturalistic vision with the idea of a scientific image potentially replacing the manifest image in the future (Sellars 1962). Gillett and Loewer state that every “era has its Weltanschauung and in much contemporary philosophy the doctrine of ‘physicalism’ plays this role”. (Gillett and Loewer 2001, p. ix). Similarly, card-carrying physicalist Daniel Stoljar admits that “physicalism is in many ways the Weltanschauung of modern analytic philosophy” (Stoljar 2010, p. 2). Jaegwon Kim begins an article stating that if “contemporary analytic philosophy can be said to have a philosophical ideology, it is, unquestionably, naturalism” (Kim 2003, p. 84). Such quotes may demonstrate that there are at least some important naturalists who are not averse to the idea of embracing naturalism as a worldview rather than a thesis.

Being considered the prevailing worldview gives naturalism a dialectical advantage. A worldview can be viewed as a kind of attitude on which we simply take certain claims as plausible, claims for which we may not be able or willing to further provide reasons as to why they are plausible. It is thus not that naturalism as a worldview is fully immune, but that it is granted prima facie plausibility as the predominant worldview. Contrast this with theism which could qualify as the dominant worldview of medieval Europe. Medieval man does not have to justify belief in God, as comes with the dominant worldview. Similarly, philosophers now rarely have to justify belief in naturalism, it comes with the dominant worldview. Naturalism as a worldview fully embraces the immunity awarded through its dominance. Even if this is not desirable, it is perhaps closest to the truth, i.e. most descriptive of the current circumstances, that naturalism is a worldview rather than a thesis or attitude.