Draft, please do not cite. From the Heterogeneity Problem to a Natural-Kind Approach to Pleasure Antonin Broi Abstract The heterogeneity problem, which stems from the alleged difficulty of finding out what all pleasant experiences have in common, is largely considered as a substantial issue in the philosophy of pleasure, one that is usually taken as the starting point for theorizing about the essence of pleasure. The goal of this paper is to move the focus away from the heterogeneity problem and toward a new approach to pleasure. To do this, I first show that, although the approach stemming from the heterogeneity problem – what I call the heterogeneity approach – has led to an interesting discussion on the essence of pleasure, it has significant methodological problems that make it unlikely to make more progress. I thus propose a natural-kind approach to pleasure, which has been surprisingly overlooked so far, and which seeks to determine what, if any, the natural kind of pleasure would consist in. This approach overcomes the obstacles which the heterogeneity approach is confronted with. It also broadens the investigation of pleasure by enabling the use of a larger range of methodological tools, thus opening new promising directions for research. 1 Keywords: pleasure, heterogeneity problem, natural kind, introspection, affective neuroscience Introduction Pleasant experiences typically include the various experiences associated with having a massage, reading a good book, playing a video game, having an orgasm, etc. While it is easy to give examples of pleasant experiences, it is notoriously difficult to identify what pleasure consists in. This question has given rise to a rich philosophical literature in recent years, leading to a variety of accounts of pleasure. The starting point for this recent philosophical debate has been the so-called heterogeneity problem, according to which the heterogeneity of pleasant experiences poses a particularly difficult challenge for defining pleasure. While the heterogeneity problem is arguably the touchstone of the recent literature on pleasure, the goal of this paper is to argue that the discussion that stemmed from it has reached its limits, and to propose a new direction for research in the philosophy of pleasure, centered around questions about the status of pleasure as a natural kind. To do this, I will first introduce the heterogeneity problem, as well as the role it has taken in the recent literature (Section 1). I will call the heterogeneity approach the approach to pleasure that takes as a starting point the heterogeneity problem. The heterogeneity approach has led to an exploration of a variety of theories about the structure of our pleasant experiences and the essence of pleasure. However, I will argue that it is unlikely to make more progress: the methodological tools that it relies on are too precarious (Section 2). To overcome this problem, I propose to reorient the debate toward a natural-kind approach (Section 3), which seeks to answer the question whether 2 pleasure is a natural kind, and, if it is, what it consists in. In doing this, we can avoid the difficulties faced by the current debate and allow for a convergence between the investigation of pleasure and that of other mental entities like beliefs, desires or emotions. 1 The Heterogeneity Problem The philosophy of pleasure is primarily interested in understanding what pleasure is. As it stands, this is a standard kind of question in philosophy, one that philosophers can ask about many different things: What is a person? What is justice? What is knowledge? In the case of pleasure, what seems to be expected from philosophers is to come up with a definition that identifies the essence of pleasure, i.e. that in virtue of which experiences are pleasant. Different accounts propose different definitions of pleasure. Why would we think that pleasure has an essence? Well, as all competent language users arguably know how to use the concepts "pleasure" and "pleasant", there must be something which explains why it is so easy to determine whether one's experience is pleasant or not. Now, in investigating the essence of pleasure we seem to be confronted with the heterogeneity problem: when we introspect our pleasant experiences, there seems to be nothing in common between them. Pleasant experiences appear to be excessively heterogeneous. It is difficult to overstate how important this problem has become in the recent philosophical literature. Virtually every article published in the last thirty years on pleasure has mentioned it more or less explicitly.1 A non-exhaustive list includes Parfit, 1984; Griffin, 1986; Feldman, 1988; Kagan, 1992; Carson, 2000; Feldman, 2004; Crisp, 2006; Heathwood, 2007; Mason, 2007; Smuts, 2011; Labukt, 2012; 1 The problem is often taken to trace back to Sidgwick's justification of his account of pleasure in terms of desirability (Sidgwick 1981, 127). 3 Bramble, 2013; Moen, 2013; Aydede, 2014, 2018; Lin, 2018. "Heterogeneity" has progressively become the standard term to refer to this problem. To give a few examples of how philosophers have introduced it, here is how Parfit, who did not employ the term "heterogeneity", put it: Compare the pleasure of satisfying an intensive thirst or lust, listening to music, solving an intellectual problem, reading a tragedy, and knowing that one's child is happy. These various experiences do not contain any distinctive common quality (1984, 492) In his 1988 article, Feldman aims to address what he calls the "heterogeneity question", which he takes to be a problem affecting sensory pleasures only: One thing to notice about sensory pleasure is its apparent heterogeneity. The man on the beach enjoys some pleasurable smells as well as some pleasurable feelings of warmth. Each of these sensations is pleasant, pleasurable, 'pleasure-giving'. Some would find nothing odd in saying that each of these sensations 'is a pleasure'. Nevertheless, from the strictly phenomenological perspective, they seem to have very little in common. One is an olfactory sensation – it is the smell of fresh, salty air. The other is an all-over bodily feeling of warmth. (1988, 60) To take a more recent example in the literature, here is how Smuts introduces it: Most philosophers since Sidgwick have thought that the various forms of pleasure differ experientially to such an extent that one cannot find a common, distinctive feeling among them. The heterogeneity of pleasurable experience is thought to make it something of a mystery as to why we call these things by the same name. This is known as the heterogeneity problem. (2011, 242) 4 In all generality, the heterogeneity problem stems from two conflicting intuitions that we have about pleasant experiences. First, that they have something in common: after all, they are arguably all occurrences of pleasure. This is the claim that we postulate when we try to discover the essence of pleasure. Second, they do not seem to have anything in common when we introspect them, that is, they seem heterogeneous. Talk of heterogeneity may be usefully reformulated in terms of similarity and dissimilarity, which are notions more commonly found in the philosophical literature and which have been subject to more philosophical scrutiny (see Cowling 2017 for a review of philosophical issues around similarity, or resemblance). This reformulation is rather innocuous: talk of similarity is often used to clarify that of heterogeneity (as the quotation further below by Smuts shows). The heterogeneity problem, as it is usually introduced in the literature, thus gives rise to a discussion about the (dis)similarity holding between different pleasant experiences. This seems like a useful way to initiate the investigation on pleasure. After all, if we want to define, say, the concept of person, we might start as well with an investigation of the similarities and dissimilarities between all the entities we consider as persons. The respect in which all these entities are similar is likely to have to do with properties essential to personhood. In other words, what all persons have in common is likely to point to the essence of personhood. In the case of the heterogeneity problem, as is clear from the quotations above, a specific take on similarity is taken for granted: it focuses on similarity in the phenomenology of pleasant experiences, i.e. in what it is like to have a pleasant experience, rather than on other features of these experiences (e.g. their relationships with other mental states). As a result, there are two standard responses to the heterogeneity problem. One is to take it as justifying the move toward an externalist, non-phenomenological conception of pleasure. This takes for granted that pleasant experiences do not have anything internal in common, and proposes instead that pleasure has to be 5 defined in terms of extrinsic properties of experiences, usually the property of being the object of a certain attitude from the subject. In other words, as Smuts puts it, "the reason we call all these different types of experiences 'pleasures' is not because of some similarity in the way the experiences feel, since they feel very different, but because of some similarity in our responses" (2011, 242). Several externalist, or attitudinal, views have been defended. Some have appealed to conative attitudes, that is, attitudes of desire (Alston 1967; Carson 2000; Heathwood 2007), others to sui generis attitudes such as liking (Parfit 2011) or the propositional attitude "taking pleasure in" (Feldman 2004). The other solution has been to resist the pressure from the heterogeneity problem, and maintain that there is some kind of intrinsic "phenomenal quality" common to all pleasant experiences after all. The standard typology of these felt-affect theories distinguishes between the distinctive feeling account (Moore 1993; Bramble 2013) and the hedonic tone account (Broad 2000; Crisp 2006; Smuts 2011). Bramble characterizes the distinctive feeling account, somewhat tautologically, as follows: "for an experience to be pleasant (or unpleasant) is just for it to involve or contain a distinctive kind of feeling, one we might call 'the feeling of pleasure itself', or simply 'the pleasant feeling'" (2013, 202). The idea seems to be that pleasure is a phenomenal quality that is somehow separated from the rest of the phenomenal experience and in particular, in the case of sensory pleasures, from the sensation that the subject takes pleasure in. This is the account that seems particularly vulnerable to the heterogeneity problem (though Bramble (2013) has argued that it has the resources to resist it). According to hedonic tone accounts, pleasure is a quality that somehow infuses our phenomenal experience. There are different ways to understand this claim. One interpretation draws on an analogy with loudness, which is arguably a dimension of all our auditory experiences (Kagan 1992). In the same way, pleasure (and displeasure) would be a dimension of all our experiences. Another interpretation draws on an analogy with colors (Crisp 2006): the 6 relationship between being colored and being red (or being blue) is a determinate-determinable relation; likewise, being pleasant would be a determinable property of many different determinate properties instantiated by the experiences we intuitively consider as pleasant. Insofar as all these accounts investigate the essence of pleasure by taking as a starting point the heterogeneity problem, they belong to what I shall call the heterogeneity approach. This approach usually leads to an investigation of how pleasant experiences are structured: felt-affect accounts put forward different ways in which a pleasant experience could somehow contain a phenomenological entity corresponding to pleasure, whereas attitudinal accounts propose that pleasant experiences are structured in a way that involves some attitude toward them. 2 The Limits of the Heterogeneity Approach The heterogeneity approach has accompanied a revival of the philosophical literature on pleasure, and sparked a fruitful debate about its essence. In this section however, I would like to highlight the limits of this approach, and argue that it is unlikely to enable us to make more progress in the future. In doing this, I shall call into question the relevance of the heterogeneity problem. I am not the first to do so, since recurring worries have been expressed within the heterogeneity approach itself. For example, Crisp describes the argument from heterogeneity as "spurious" (2006, 629), and Smuts claims that "the heterogeneity problem is not a genuine problem" (2011, 242). My arguments can be understood as an attempt to ground them in more general methodological worries. Though there are a variety of considerations that have been brought up to support or undermine specific accounts of pleasure within the heterogeneity approach, two kinds of considerations which have played a particularly important role: armchair introspective evidence and theoretical 7 assumptions about the mind, notably about how attention works and about the structure of our pleasant experiences. I will review them successively and show that they are both problematic. As already seen in the previous section, the heterogeneity problem invites us to use introspective evidence to compare the phenomenal character of different pleasant experiences, in order to subsequently attempt to isolate the phenomenology of pleasure. This raises the question of how reliable our introspection is when it comes to introspecting our pleasant experiences. I would like to argue that it is unreliable when it is used for the purposes of discovering the structure of our pleasant experiences. In recent years the epistemological ambition of introspection in general has been subject to considerable scrutiny. Schwitzgebel (2008), in a much-discussed paper, argued that introspection is unreliable most of the time, and there has been an ongoing debate around this question since then. More to the point, Haybron (2007) argued that we are often mistaken about our affective states, so that we are subject to what he calls affective ignorance. Many authors within the heterogeneity approach have also brought up similar worries about our introspective capacities in general (e.g. Smuts 2011; Labukt 2012; Bramble 2013). For example, one difficulty identified by Smuts has to do with remembering our past pleasant experiences. According to him, it implies that "[i]t is unreasonable to expect that people can clearly identify a common phenomenal aspect among experiences that they cannot recall with any level of specificity for much time at all." (2011, 256) While these worries may give us prima facie reasons to be pessimistic about how far we can go in investigating pleasure through armchair introspection, objections usually proceed by pointing out the extent of introspective disagreements, that is, disagreements among philosophers over what introspection tells us about the mind. Of course, one might argue that introspective disagreements are to be resolved in the course of philosophical discussion. For example, Bayne and Spener (2010) claimed that some introspective disagreements could be simply due to terminological variation 8 among participants in the debate, or to the influence of background commitments and expectations. Still, the more widespread introspective disagreements are over a topic of research, the more concerned we should be about our capacities to make genuine progress on this topic. When it comes to the heterogeneity approach to pleasure, there are long-standing disagreements about whether pleasant experiences seem heterogeneous in the first place. In other words, there are disagreements about whether there is something phenomenal in common between our pleasant experiences. As noticed by Labukt, "some philosophers claim to know through direct selfobservation that their pleasant experiences all have the same hedonic tone and others that they don't" (Labukt 2012, 179). To give a few examples, Moen, talking about our intuition of the unity of pleasures, writes: Looking at pleasures first, it seems that the taste of ice cream, the feeling of being loved, and the excitement of reading a detective story-although these differ in many respects-do share a certain quality (perhaps a certain kind of positive buzz), and it seems to be by virtue of sharing this quality that they are pleasures and that we are able to reliably pick them out as such. (Moen 2013, 528) By contrast, Bain and Brady, for example, take the "non-phenomenality" of pleasure as a feature that a satisfactory theory of pleasure would have to account for (Bain and Brady 2014, 5). Nonphenomenality implies that pleasure is not a common phenomenal quality of pleasant experiences. I would like to suggest that this disagreement, as well as other disagreements between partisans of different accounts of pleasure (e.g. between hedonic tone and distinctive feeling theorists), may ultimately trace back to our tenuous introspective access to the structure of our pleasant experiences. If this is true, introspective disagreements within the heterogeneity approach are unlikely to be solved through armchair introspection. I certainly do not deny that we do have some 9 sort of introspective access to the pleasant character of our experiences. Otherwise, how would we come to know that our experience is pleasant or not, or that an experience is more pleasant than another? However, when it comes to determining the metaphysical status of pleasure within our experience, introspection seems to flounder: the structure of our pleasant experiences is not introspected in a way that can lend support to any specific account of pleasure. Perhaps this is just an example of a more general failure of introspection, but I am open to the possibility that there might be a special difficulty related to the introspection of affective states. To illustrate this, suppose that felt-affect theories are right, so that pleasure is a phenomenological entity. How exactly could introspection help us decide between the different feltaffect theories in competition? It seems to me that whether pleasure is a distinctive feeling, a dimension or a determinable of our experience could not be settled on introspective grounds only. This is suggested by my own attempts at introspecting my pleasant experiences, but it is also in line with many remarks made within the heterogeneity approach.2 Part of the difficulty may lie in the ignorance of what introspecting our pleasant experience would be like if, say, the determinatedeterminable account of pleasure were true: it is not clear whether we are able to recognize through introspection a determinable property of our experience. More importantly, different accounts entail different modal claims about pleasant experiences. That pleasure is a distinctive feeling may be understood as implying that it is possible for pleasure to occur independently from the rest of the experience, which is ruled out if pleasure is a dimension of our experience. But introspection does not give us access to modal facts about our experience! From what we introspect, there does not seem to be any straightforward inference toward what our experience could be. If this is true, then we seem to be confronted with a fundamental epistemological problem when trying to put 2 For example, Carson notes that "[t]he feeling tone of pleasantness, if it exists at all, is a subtle and elusive quality of our experience that is difficult to isolate" (2000, 14). Talking about whether there is heterogeneity in our pleasant experiences, Labukt concedes that his "own attempts to answer it through introspection have so far been inconclusive" (Labukt 2012, 179). 10 introspective evidence to bear on candidate accounts of pleasure. Overall, the precise articulation between pleasure and the rest of our phenomenal experience appears to be largely hidden to the subject, so that further use of armchair introspective evidence is unlikely to yield much more progress. To make up for the limits of introspection, discussions within the heterogeneity approach have relied on other considerations and background assumptions. The most common auxiliary assumptions have to do with how attention and introspection work.3 Unfortunately, many of the assumptions commonly appealed to are insufficiently motivated, so that the arguments that build on them rest on shaky grounds, or so I will argue. Since an exhaustive review is beyond the scope of this paper, I will focus on three such assumptions found in the heterogeneity approach, which stand out either for their representativeness or the important role that they have played in the debate: 1. The heterogeneity problem is largely taken to imply that there is no phenomenal quality of pleasure that we can introspectively isolate, that is, focus our attention on it alone. This in turn is taken to discredit at least a crude distinctive feeling theory. The underlying assumption seems to be that if pleasure were a distinctive feeling, understood as an independent component of our experiences, then we would be able to introspectively isolate it. Our alleged failure to do so would then justify the move to hedonic tone theories, which are arguably less demanding in this respect (though one could claim that they too are undermined by the same argument). However, the assumption that we can introspectively isolate all the components of our experiences, which is required for this move, seems unwarranted. For example, it is common to hold that experiences of flavors are composed of both taste and smell properties (Smith 2015), where taste properties include 3 In addition, one might think that general considerations about the structure of our experience may usefully constrain our accounts of pleasure. For example, if we think that there is no determinate-determinable relation in our phenomenology (perhaps because we think that there is no determinate-determinable relation tout court) Crisp's account seems to be straightforwardly undermined. This might be the spirit of Bramble's objection against Crisp's proposal (2013, 207–8). The problem is that the structure of our experiences in general is itself a very controversial issue, so it is a problematic ground to build an argument on. 11 sweetness or bitterness. The flavor of a strawberry, for example, would not be an unanalyzable phenomenal quality. Nevertheless, we cannot introspectively isolate the smell components from the taste components of the flavor of a strawberry. As Smith puts it, "[o]nce taste and smell fuse into an experience of flavour, it is no longer possible to separate out the different components by phenomenological decomposition." (Smith 2015, 323) This is supported by the fact that people who gradually lose olfaction, a condition known as anosmia, tend to report first their incapacity to taste flavors. Likewise, though the phenomenal quality associated with hearing a chord is certainly composed of different, independent notes that a trained musician can easily distinguish, many inexperienced people are unable to do so. While these putative counterexamples do not definitely rebut the assumption that we can introspectively isolate the components of our experience, they do shed doubt on the most central argument in the heterogeneity approach. 2. In arguing against the distinctive feeling theory, Smuts (2011, 255) apparently endorses an argument made by Alston which is based on an implausible assumption about how attention works. Alston (1967) argued that if pleasure were a distinctive component of our experiences, it would be a distraction, that is, something we would tend to focus our attention on.4 But, the argument goes, pleasure is not a distraction: if I am playing video games in a pleasant state of flow, I am not tempted to stop playing to attend to the pleasant character of my experience. Of course, I know that the pleasant character of the experience would stop should I stop playing. But, more fundamentally, the pleasant character of my experience does not capture my attention. Although he does not develop the argument in much detail, its success clearly depends on the assumption that there is a direct relationship between the "size" of a phenomenal component and how much attention it draws: the larger the component of our experience, the more our attention would be repeatedly drawn to it. This is a substantial assumption about how attention works, and it is far from obvious. 4 This may be inspired by a well-known argument developed by Ryle to defend his dispositionalist view of pleasure (Ryle 2009). 12 One might think that a phenomenal component which continuously grows in our consciousness could go unnoticed, since no sudden change would attract the subject's attention (especially if, as it is the case in the state of flow, her attention is already focused on the activity that she is immersed in). Perhaps one could take it to be true in virtue of what attention does: what is attended to becomes a bigger component of one's experience. But again this would be a controversial assumption about the relationship between attention and consciousness, which is the object of a large literature in philosophy of mind (see Watzl 2011 Section 3; Mole 2017 Section 3.1 for brief introductions about this topic). In any case, it is not an assumption that has enough support to draw a conclusive argument against any theory of pleasure. 3. Finally, let us focus on Bramble's "reflective blindness" objection against attitudinal views (2013, 2016, 2019). It is based on two conflicting premises. First, he argues that we are sometimes unaware of our sensory pleasures while they occur. He draws on alleged examples from Schwitzgebel and Haybron's works. Haybron's examples include those affective states that "exceed our powers of discernment even while they are occurring" (Haybron 2008, 222). For example, Perhaps you have lived with a refrigerator that often whined due to a bad bearing. If so, you might have found that, with time, you entirely ceased to notice the racket. But occasionally, when the compressor stopped, you did notice the sudden, glorious silence. You might also have noted, first, a painful headache, and second, that you'd had no idea how obnoxious the noise was – or that it was occurring at all – until it ceased. But obnoxious it was, and all the while it had been, unbeknownst to you, fouling your experience as you went about your business. In short, you'd been having an unpleasant experience without knowing it. (2008, 205) Second, Bramble advances that "one can hardly have the relevant kind of attitude (be it 13 disliking, not wanting, disvaluing, or whatever) toward an experience that one is entirely unaware of" (his italics, 2013, 204). In his initial paper, this claim is taken to be intuitive enough on its own. The problem for attitudinal theories, then, is that they cannot account for pleasures that we are unaware of, and Bramble takes this to be "a decisive objection" against them (p. 203). This objection has been criticized in recent articles by Heathwood (2018) and Feldman (2018). Heathwood makes a distinction between weak and strong awareness, and argues that the fact that we are weakly aware of the experiences in question in Bramble's argument is sufficient for our having the relevant attitude toward them. Feldman, on the other hand, denies the existence of pleasures of which we are unaware: of the experiences mentioned by Bramble, he pursues, either we are aware of them or they are not (un)pleasant. A detailed examination of the argument would be beyond the scope of this paper, but I would like to briefly suggest that both premises are either underspecified or lack adequate support, especially in the light of the relevant literature in philosophy of mind. The first premise in Bramble's argument, that there are pleasures of which we are not aware, suffers from considerable ambiguity (not much alleviated by Heathwood's subsequent distinction between weak and strong awareness). Though Bramble seems to take awareness as a non-problematic notion, it has been subject to much debate in philosophy of mind. By asking about the kind of awareness we can have toward some of our peripheral experiences, it is thus clear that Bramble touches on difficult issues involving the relationship between attention, awareness, and consciousness, that are in no way specific to pleasure. Bramble's idea seems to be that the pleasant experiences of which we are unaware still belong to our phenomenal experience.5 The problem is that there is clearly a sense in which we are always aware of our phenomenal experience.6 To avoid 5 Talk of pleasant experiences is best understood as implying the existence of a phenomenology, since the term "experience" is usually taken to refer to phenomenal experience. In addition, he draws on an example by Schwitzgebel which explicitly mentions a phenomenological state. 6 Block (2007), for example, talks of "Awareness" to refer to this sense of awareness associated with phenomenal experience. 14 contradiction, Bramble has to maintain that there is another sense in which we remain unaware of these pleasures. In philosophy of mind, following the well-known (but controversial) distinction by Block (1995), phenomenal consciousness is often contrasted with access consciousness, which has to do with availability of the conscious state for use by different cognitive functions, such as memory, reasoning and decision-making. On this interpretation of awareness, a subject is aware of something only if she can use it for various cognitive purposes. The existence of mental states which are phenomenally conscious but not access conscious is controversial, as well as their relationship with attention.7 In addition, a more cognitively sophisticated kind of awareness is sometimes hinted at: in Haybron's previous example above, it is emphasized that the subject did not know that she was having an unpleasant experience, and "Unknown Pleasures" is also the title of Bramble's 2019 paper in which he responds to Heathwood and Feldman's objections. Now, talk of "knowing" seems to imply a more sophisticated cognitive awareness than either phenomenal consciousness or access consciousness. Knowing something arguably requires holding a propositional attitude. As a result, there is nothing contradictory about having a pleasant experience (with phenomenal awareness) available for further cognitive processes (with access awareness) but nonetheless "unknown" by the subject. In any case, without more precision on the kind of awareness that Bramble is concerned with, it is difficult to properly assess the cogency of the premise. While the second assumption – that one cannot have a liking or desire attitude toward an experience which we are unaware of – has apparently been accepted by all participants in the debate, it strikes me as unmotivated, whatever the sense of unawareness at play. Perhaps Bramble has in mind a picture of attitudes as voluntary, effortful mental acts, in which case it is natural to 7 Block mentions a case similar to Haybron's refrigerator example, which he interprets as involving phenomenal consciousness without access consciousness (Block 1995, 234). See Schlicht (2012) for a review of different alternative interpretations of this case. 15 suppose that the subject must have a prior awareness of something before holding an attitude toward it. But I do not see any reason to accept such a restrictive view on attitudes.8 In a subsequent article (Bramble 2016), he argues that denying the assumption has undesirable consequences: since we have a lot of subtle, peripheral pleasures and pains at all times, accepting that we have some attitude toward each of them would lead to an implausible inflation in the number of attitudes that a subject has at a given time. But why is such a "rich" view about attitudes implausible? The only (brief) justification given by Bramble (in his 2019 article, ft 16) is that this objection runs parallel to a similar objection made against higher-order theories of consciousness. Indeed, these theories claim that conscious states are just those states which are the object of a (higher-order) attitude from the subject. They thus require the existence of a very large number of (higher-order) attitudes toward (first-order) mental states to account for the variety of our conscious states. It has been objected that it is implausible to suppose that the subject can have so many higher-order attitudes. But the success of this objection against higher-order theories of consciousness is itself controversial, and Bramble says little to support it. As a result, endorsing it and building on it to develop a different objection, this time against some specific accounts of pleasure, amounts to cherry-picking. What stands out from the debates over the three assumptions reviewed is how isolated they have been from other relevant domains of research. Since they take a stand on complex, unresolved issues related to introspection, attention or the structure of our experiences, they do not properly belong to the philosophy of pleasure. However, there seems to be no consistent attempt to engage with the existing debate on these questions. While it is difficult to draw a general conclusion from 8 One might try to defend the assumption by claiming that it is the attitude itself that makes the subject aware of its object. This would be a standard claim for representationalists (such as Tye 1995), who argue that conscious states are states that represent something else, but this is clearly not the framework that Bramble operates with. In addition, Bramble's assumption might introduce an asymmetry with pro-attitudes whose object is not experiential. If I desire that my friend come to visit me tomorrow, I arguably do not have a prior awareness of the proposition that my friend comes to visit me tomorrow before I have the attitude of desire toward it. This means that the assumption must hold only for pro-attitudes with experiential objects. 16 an examination limited to a few assumptions, I tentatively conclude that some key theoretical considerations in the heterogeneity approach rest on shaky foundations. This has damaging consequences. The use of ad hoc auxiliary assumptions about introspection, attention, and the structure of our experiences makes it easy to defend different accounts of pleasure. Consider the following defense of the distinctive feeling account by Bramble: if the distinctive feeling theory is true, we should not expect to be able to gain a clear sense of 'the pleasant feeling', or the way in which all pleasant experiences feel alike. The reason is that, if the distinctive feeling theory is true, most instances of 'the pleasant feeling' are, taken by themselves, virtually imperceptible. They occur in extremely small quantities (or low intensities), and in very abstract or ethereal locations in one's experiential field, locations that are not at all easy to direct one's attention toward, or focus upon. What does a pleasant experience of sunbathing have in common phenomenologically with one of drinking a cool beer on a hot day? Just that it has a whole lot of these tiny, independently virtually imperceptible, feelings scattered throughout it. (Bramble 2013, 210) He makes clear that introspection cannot help us to confirm or infirm his account: our failure to identify these "tiny, independently virtually imperceptible, feelings" can be explained by the limits of our introspective capacities. In doing this, he has to make controversial metaphysical assumptions: are there really "ethereal locations" in our conscious experience "that are not at all easy to direct one's attention toward"? Why would the small quantities of pleasure scattered throughout our experiential field aggregate in a way that nonetheless cannot be introspectively isolated? These considerations play a crucial role in his defense of the distinctive feeling account, and yet lack independent support. As a result, they seem arbitrary. 17 I conclude that the heterogeneity approach relies heavily on debatable armchair introspective evidence and problematic theoretical assumptions. This suggests that the heterogeneity approach might have an overly limited evidential basis, insufficient to successfully decide between the different accounts in competition. As a result, it is unlikely to make further progress. 3 Toward a Natural-Kind Approach Up to now, my results are rather negative. I have attempted to show that the heterogeneity approach to pleasure may have come to a standstill. I turn now to the positive argument of this paper. I would like to introduce a new direction for research, one that moves the focus away from introspective considerations about the phenomenological similarity of our pleasant experiences and allows for a better connection between the philosophy of pleasure and the rest of philosophy of mind: a naturalkind approach.9 To be clear, this new approach does not enable us to decide between the different accounts highlighted by the heterogeneity approach. Rather, it asks new questions about pleasure, ones on which we may be able to make more progress. Importantly, these questions still have to do with the nature of pleasure. What Is a Natural-Kind Approach? 9 I am not the first to put forward a natural-kind approach to pleasure: Katz (2016) explicitly evokes in passing the idea that pleasure may or not be a natural kind. More recently, valence has been treated as a natural kind by Carruthers (2018). At the beginning of his paper he characterizes valence as "pleasure and displeasure". Because he is primarily interested in a technical concept used by psychologists, and not in the common-sense notion of pleasure or the one relevant to ethical theorizing, he takes a slightly different perspective on whether pleasure (and displeasure) is a natural kind. 18 Natural kinds are categories which carve nature at its joints. They are determined by the way the world is structured, rather than by the interests of the subject doing the categorization. In other words, there is something objective about natural kinds, which explains why discovering and studying natural kinds is often considered as an important task for scientific inquiry. In particular, natural kinds are taken to support inductive generalizations across their members: that one member has property P can be taken as evidence that most of the other members have P too. Paradigmatic examples of successful natural kinds include chemical elements such as gold or helium: different individuals of the same chemical element have in common a specific microphysical organization, that distinguishes them from individuals of any other chemical element. In this sense, different instances of gold or helium share the same essence. Other kinds, like biological species, have a more disputed status (Bird and Tobin 2018). For biological species and many other kinds found in special sciences (biology, social sciences, etc.), it is generally recognized that talk of essence, which points to a set of necessary and sufficient conditions for something to belong to the kind, has to be abandoned, but this does not necessarily threaten their status as natural kinds (more on this below). In the case of pleasure, asking whether it is a natural kind thus amounts to asking whether there is something objective about the way we categorize all occurrences of pleasure under the same category, and asking what the putative natural kind of pleasure would consist in amounts to asking in virtue of what pleasure would be a natural kind. As I said earlier, the heterogeneity approach was rooted in questions about the similarity between pleasant experiences. The natural-kind approach could be understood as a new, more comprehensive attempt to investigate this similarity. As will become clearer later, this may redirect philosophers' attention toward currently relatively overlooked topics of inquiry. A natural-kind approach to pleasure would enable a convergence with many debates over other mental entities in philosophy of mind. Indeed, it is common in many areas of philosophy of mind to 19 ask about the natural-kind status of mental entities belonging to folk psychology, such as desire (e.g. Schroeder 2004), memory (e.g. Michaelian 2011), concepts (e.g. Machery 2005), emotion and its discrete categories like anger or sadness (for influential discussions, see Griffiths, 1997; Barrett, 2006), or mental entities postulated by scientific research, such as clinical depression and other nosological categories (see Kincaid and Sullivan 2014). In contrast, as is shown by the examples developed in the last section, it is striking that the investigation of pleasure has comparatively remained this isolated from philosophy of mind, psychology and neuroscience (important exceptions aside, such as Aydede 2000, 2014, 2018; Crisp and Kringelbach 2018; Katz 2016).10 This can be explained by the fact that recent works on pleasure within the heterogeneity approach stem from ethics (as noted by Aydede 2014, 12). The discrepancy in treatment between the concept of pleasure and other folk-psychology mental concepts is all the more unfortunate since the concept of pleasure seems comparatively to be more amenable to a natural-kind approach. Indeed, some mental concepts are used in so many different contexts, and in seemingly so many different senses, that they are suspicious candidates for being natural kinds.11 In contrast, the concept of pleasure seems to be well-delimited, and thus more likely to pick out a natural kind, as evidenced by the relative consensus over which experiences count as pleasant (also noted by Carson 2000, 13). The natural-kind approach is most distinctive in the methodological tools that it brings to the investigation of pleasure. Indeed, in accordance with its naturalistic perspective, the natural-kind approach makes use of a wide variety of empirical methods and results. In the case of pleasure, rather than primarily appealing to armchair introspective evidence and theoretical considerations, philosophers could additionally draw on empirical research from psychology and neuroscience. To get a grasp of the variety of these methods and results, let us give a few examples of the potentially 10 Note that the heterogeneity approach has also been disconnected from the literature concerned with displeasure, arguably the opposite of pleasure. For example, there is a thriving literature on pain in philosophy of mind (see Corns 2018 for a recent review). 11 For example, Schueler (2011) denies that the concept of desire is suited for a natural-kind approach, while Haybron (2008 Chapter 2) notes the special difficulty in asking what happiness is, due to the diversity of its meanings. 20 relevant research. Insofar as pleasure, together with other affective states, plays a crucial role in motivating and directing the individual's behavior, it can be investigated in terms of how it affects the individual's chances of reproduction and survival. For example, pleasure is directly involved in homeostatic processes, i.e. those processes that enable the organism to retain some key biological parameters within desirable bounds. Evolutionary considerations, by pointing to the adaptive function of pleasure, might illuminate the role of pleasure in our mental life (for example LeDoux 2012; Dickinson and Balleine 2009). In psychology, the behavior of individuals has long been interpreted as directed toward obtaining reward stimuli, such as food or sex, which are usually understood as pleasure-giving rewards. With the rise of neuroscience, it has become possible to investigate the neurobiology underlying this reward system. It has been done in the growing field of affective neuroscience, which has discovered several brain areas involved in the production of pleasant experiences, as well as different components in the reward system, which may give rise to different felt qualities in our phenomenal experience (for a summary of the main results of affective neuroscience on pleasure, see Berridge and Kringelbach (2015)). Together with results from neuroeconomics, which is concerned with investigating the brain processes underlying decisionmaking, notably so-called value-based decision-making, the neural substrates of pleasure can be investigated in a way that is likely to illuminate its nature (see for example Glimcher and Fehr 2014). As already mentioned, many philosophers of pleasure currently make heavy use of armchair introspection, which is prone to various biases. However, there have been attempts to use more rigorous introspective reports to inform our theories of affective states (see Miskovic, Kuntzelman, and Fletcher 2015 for a discussion of how affective neuroscience currently deals with subjective experience of affect.). For example, Colombetti (2013) has defended the use of firstand second21 person methods to investigate the bodily character of our affective experiences. By enriching the range of considerations drawn upon in the philosophical investigation of pleasure, the natural-kind approach would appear to have the potential to solve the methodological impasse. Some Objections Against the Natural-Kind Approach Before I go on to explore some implications of the natural-kind approach, I would like to respond to a few potential objections. The variety of considerations just outlined gives rise to the problem of how we should weigh them against each other. Should some of them prevail over others? Natural-kind approaches in general are sometimes criticized as surrendering the philosophical investigation to scientists.12 Indeed, since most of the distinctive methodological tools brought by the natural-kind approach come from scientific research, it could be argued that this approach amounts de facto to giving up the philosophical investigation of pleasure to scientists, so that the concept of pleasure would end up referring to whatever scientists are referring to with this concept. As a result, one could worry that a natural-kind approach puts too much – illegitimate – responsibility in scientists' hands. I would like to briefly argue that this is not the case. While some concepts like that of water have been taken over, so to say, by scientists, the concept of pleasure is unlikely to undergo the same fate. The subtleties of the common-sense notion of pleasure and its importance for ethics justify that philosophers take a significant part in its investigation. In addition, there are notoriously difficult philosophical issues when it comes to mental concepts belonging to folk psychology in general, 12 See Griffiths (2013) for an interesting review of the opposition between naturalistic and non-naturalistic approaches to affective states. 22 notably due to their use in ordinary explanations and predictions and our alleged first-person access to what they refer to.13 Overall, this suggests that the epistemic authority of scientists on these questions may be greatly limited. This general response might not satisfy the critics, who could still argue that it is unclear why scientists (or scientifically informed considerations) should have any say in defining pleasure, since their purposes are so different from philosophers'. Although it is true that, in the end, both scientists and philosophers want to elucidate what pleasure is, one could object that the move towards the natural-kind approach would give up on important aspects of the original purpose of the philosophical investigation of pleasure. Let us review two versions of this objection. Since many philosophers investigating the nature of pleasure, especially within the heterogeneity approach, think that pleasure is a phenomenological entity, primarily accessible from a first-person point of view, it could be argued that the natural-kind approach would not do justice to this idea. Insofar as the natural-kind approach is naturalistic at its core, and that phenomenological entities are notoriously difficult to accommodate within naturalistic frameworks, it would ensue that the natural-kind approach is not suited for the task of finding out what pleasure is. While I do think that there are additional difficulties raised by the putative phenomenological aspect of pleasure, I do not think that it is enough to undermine the prospects of the natural-kind approach. First, it should be emphasized that its phenomenological aspect is itself fairly contested, as I have already shown. It would be unreasonable to take it for granted. Second, its phenomenological aspect may not be an unanalyzable feature. Perhaps it can be accounted for by other aspects of pleasure: the phenomenology of pleasure could be e.g. desire-like. Third, other mental states that arguably have a phenomenological aspect, such as perceptual states or pain, have been subject to scientifically informed philosophical accounts as well. Fourth, whether the putative 13 See Murphy (2017) for a review of different positions about the integration of folk psychology with empirical psychology and neuroscience. 23 phenomenological aspect of pleasure is adequately taken into account depends mainly on how the considerations outlined above are combined. In other words, it is up to philosophers to give pride of place to a priori considerations in their natural-kind investigation of pleasure. Fifth, the gap between non-scientific and scientific considerations is not to be exaggerated. For example, is there really a gap between armchair introspection-based considerations raised by philosophers and more rigorous introspection-based methods developed by scientists? A second variant of this objection is that the natural-kind approach loses sight of the normative significance of pleasure, which is what gave the initial impetus to the heterogeneity approach. It is true that the literature on pleasure has long been primarily about ethics – Crisp (2006) still introduces his own theory of pleasure for the sake of supporting a hedonistic theory of well-being –, but it has since then become largely autonomous, so there is no reason to keep the discussion within the bounds of ethics. But there is perhaps a more specific objection stemming from this general worry. Many philosophers (including Crisp 2006; Labukt 2012; Smuts 2011) define pleasure in a way that makes crucial use of the normative aspect of pleasure. One problem could be that naturalistic approaches cannot make sense of this essential normative aspect of pleasure. According to Labukt, It is also doubtful whether the normative hedonic tone view [i.e. his theory of pleasure] is compatible with a naturalistic account of goodness. A naturalist cannot claim that positive hedonic tones are united by possessing some very special non-natural and irreducibly normative property. He would have to maintain that the goodness of the positive hedonic states is a purely natural phenomenon. [...] It seems, then, that the property that, according to the normative hedonic tone view, unites pleasant and painful experiences must in some sense be irreducibly normative. It is not identical with any purely natural or factual properties of hedonic states (2012, 191) 24 In moving to the natural-kind approach, there seems to be no longer any room for this kind of views. I agree that Labukt's view is not compatible with a natural-kind approach to pleasure. However, his idea that the normative essence of pleasure is wholly non-natural and irreducible to any natural property is rather uncommon. A detailed examination of Labukt's interesting proposal would take me too far, but most philosophers would accept, contra Labukt, that the putative normative essence of pleasure would still at least have to supervene on natural properties. As soon as we accept this fairly weak commitment, we can confidently proceed to a natural-kind approach to pleasure. In sum, I think that the range of views that are ruled out by the natural-kind approach is limited to implausible views. In contrast, the idea that pleasure has (perhaps essentially) normative properties is not ruled out.14 Some Directions for Research in the Natural-Kind Approach to Pleasure Now that the guiding principles of the natural-kind approach have been clarified, I would like to say more about promising directions for research within a natural-kind approach. First, it is important to note that, strictly speaking, many accounts developed within the heterogeneity approach may still be included within the natural-kind approach. For example, feltaffect accounts, according to which pleasure just is a phenomenal quality, could be understood as a broadly essentialist answer to the natural-kind question: all and only occurrences of pleasure would share this phenomenal quality. But, in addition, the natural-kind approach extends the range of accounts of pleasure in interesting ways. Indeed, natural-kind research usually starts with the observation of a diversity of co-occurring properties that the alleged members of the kind tend to 14 The notion of normative kind has been proposed for kinds which are partially defined in terms of their normative role (P. E. Griffiths 2004). I leave open the possibility that pleasure be some sort of normative kind. 25 share. One of the important tasks of the natural-kind approach is then to explain this cluster of cooccurring properties. For example, water (in its liquid state) is associated with manifest properties such as being transparent, being drinkable, etc. The discovery of the essence of water – H2O – made it possible to explain these various manifest properties. Likewise, occurrences of pleasure are associated with a variety of manifest properties, though this is sometimes obfuscated in the philosophical literature. Let us review the most salient ones. The relevance of each of these manifest properties may of course be questioned, but I take them to be commonsensical intuitions that we have about pleasure. To start with, pleasure is instantiated in conscious occurrences, which justifies our talking about pleasant experiences in the first place. This implies that the subject can become aware of the pleasant experience at the moment in which it occurs.15 Not only is pleasure taken to be conscious, but also phenomenally conscious. This suggests that pleasure is associated with phenomenological properties, i.e. what pleasant experiences putatively feel like. Conative (or motivational) properties are those properties that pleasure has in virtue of its relationship with desires and motivation: we tend to have various sorts of desires that involve pleasant experiences, including the desires that the pleasant experience occur and persist, but also desires whose satisfaction produces pleasant experiences, like the desire to get a promotion or to relieve one's thirst. Cognitive properties of pleasure include the property of being positively appraised by the subject, and subsequently becoming the object of a representation that will contribute to the orientation of future behavior. Finally, normative properties have to do with pleasant experiences being arguably intrinsically good, providing normative reasons to act in certain ways, etc. A satisfactory account of pleasure aims at explaining these co-occurring properties. Most existing accounts of pleasure in the philosophical literature define pleasure in terms of only one of 15 On one interpretation, this intuition directly contradicts Bramble's claim that there are pleasures of which we are not aware. This is fine: after all, Bramble's claim is indeed counterintuitive. 26 these properties, which is taken to be the essence of pleasure: they can be thought of as singlefeature accounts of pleasure. Roughly, felt-quality accounts take the phenomenological aspect of pleasure to be essential, while desire-based accounts take the motivational aspect to be essential. They then go on to attempt to explain the other manifest properties associated with occurrences of pleasure in terms of this single feature identified as essential. But this is a difficult task, which is why objections against accounts of pleasure often proceed by pointing out that they fail to explain some manifest property associated with occurrences of pleasure. For example, Bramble mentions Findlay's objection against felt-quality accounts, which questions the capacity of these accounts to explain why we want pleasure (Bramble 2013, 212). Symmetrically, desire-based accounts are often criticized on the basis that they fail to account for the phenomenological aspect (Aydede 2014, 124). By contrast, the natural-kind approach brings with it new ways of dealing with this variety of manifest properties. On one of the main theories of natural kinds, the Homeostatic Property Cluster view (Boyd 1991), the co-occurring manifest properties are to be explained by appeal to an underlying causal mechanism, which may then be what grounds the natural kind.16 In the case of mental entities, the underlying causal mechanism is often characterized as a neurophysiological or neurofunctional entity, whose role in the brain would explain the manifest properties of pleasure.17 In the case of pleasure, although it is surely too soon to draw any definitive conclusion, affective neuroscience has investigated the neurobiological substrates of pleasant experiences and identified several processes in a distributed network of brain areas which are involved in the production of pleasant experiences. There is evidence suggesting that the same brain areas are responsible for a large variety of pleasant experiences (Berridge and Kringelbach 2015). This has been interpreted as supporting the existence of a "neural common currency", which in turn would favor the view that 16 It should be noted that, in the philosophical literature, Edwards (1979) has brought up the idea that occurrences of pleasure share a family resemblance. The Homeostatic Property Cluster view can be thought of as extending this idea by postulating the existence of an underlying mechanism that explains this family resemblance. 17 This is for example how Schroeder (2004) proceeds for desire. 27 all occurrences of pleasure fall under the same category, and thus that pleasure is a natural kind. There are significant issues that will need to be solved in the course of the natural-kind investigation, and which would provide promising directions for research for philosophers. Let us focus on two examples.18 First, how exactly do motivational aspects contribute to pleasure? As already mentioned, research has shown that the reward system may be decomposed into various processes, which often occur simultaneously during an ordinary occurrence of pleasure: "liking", "wanting" and learning processes (Berridge & Kringelbach, 2015, the quotation marks distinguish the liking and wanting in question from their ordinary counterparts). The "wanting" component is interpreted as what underlies craving. It adds "a visceral omph to mental desires" (Berridge 2009, 378–9). By contrast, the "liking" component is often considered to be what gives rise to the pleasant experience itself (what is sometimes called the "hedonic impact" of the reward). Interestingly, the two components can be decoupled under certain circumstances: for example, in cases of addiction the "wanting" attitude can occur without "liking". Now, the distinction between the two may have interesting consequences concerning the role of the motivational aspect of pleasure.19 It seems to show that pleasure and desire are not as tightly connected as one could intuitively think, casting doubt on one of the commonsensical features associated with pleasure. Of course, it also bears directly on the plausibility of desire-based theories of pleasure. What if it turns out that the "wanting" attitude underlies most of our intuitions in favor of these theories? If we think that occurrences of pleasure should be identified with occurrences of the "liking" attitude only, it would ensue that most of the intuitive support for desire-based theories collapses. Second, are unconscious pleasures possible? We have seen that the idea of pleasures of which we 18 Other issues that could benefit from a natural-kind approach includes the relationship between pleasure and displeasure. One might argue against the natural-kind status of pleasure on the basis that it is pleasure and displeasure together that properly constitute a natural kind (as Carruthers 2018 seems to proceed). 19 Berridge (2009) discusses a series of other philosophical implications drawn from these results. 28 are not aware has been at the center of Bramble's objection against attitudinal theories, but these pleasures were still thought to belong to our phenomenal experience. However, the issue of unconscious pleasures also extends to putative cases of pleasures which are not even phenomenally experienced. Neuroscientists sometimes argue for the existence of the latter by appealing to evidence to the effect that the brain processes which underlie ordinary occurrences of pleasure may also be activated in the absence of conscious experience (for a review of neuroscientists' views on the topic, see Kringelbach and Berridge 2009, 7–8). Berridge concludes that "independent evidence for unconscious 'liking' reactions, even if rare, must force us to expand our definition of pleasure." (Kringelbach and Berridge 2009, 7) Indeed, it has been shown that there are cases of subliminal affective priming, where subjects are subliminally presented with happy or angry emotional facial expressions, which produce a hedonic reaction that has an influence on the subject's subsequent behavior and preferences without a corresponding conscious experience (K. Berridge and Winkielman 2003). Now, we might be reluctant to accept the existence of such pleasures. This is because pleasure is intuitively thought to be a phenomenally conscious mental state. So, is unconscious pleasure a contradiction or not? Answering this question requires to decide how revisionary we want to be with respect to our commonsensical understanding of pleasure, but also to explore further the ethical significance of pleasure. For example, one might accept the existence of such pleasures if we think that phenomenally unconscious pleasures can be good for the subject having them. Finally, what if it turns out that pleasure is not a natural kind? This could be a reason to adopt an eliminativist position, according to which talk of pleasure should be entirely abandoned. It would also be of extreme significance to ethical theorizing, insofar as it may shed doubt on the many ethical theories, notably (normative) hedonism and classical utilitarianism, which assign a central role to pleasure. The philosophical discussion could then usefully focus on identifying putative 29 adjacent natural kinds, that is, natural kinds that overlap with the extension of our ordinary or normatively relevant concept of pleasure, and which might possibly explain our false impression that pleasure itself is a natural kind. The purpose of philosophical work could then become thoroughly revisionary. Conclusion In this paper, I have advocated a new approach to pleasure, one that better acknowledges the fact that pleasure is a multifaceted mental state, and that its diverse facets can all be contested. In doing this, it builds on the rejection by the heterogeneity approach of the naive picture of pleasure as a non-problematic phenomenal quality. In recent years, there has been an impressive surge in the number of works purporting to study the natural-kind status of a wide variety of entities. Since the notion of natural kind has been subject to important evolutions and amendments20, and associated with a wide array of epistemological and metaphysical positions, this move may be considered as mere posturing. I hope to have provided enough reasons to think that, in the case of pleasure, a natural-kind approach is more than a sleight of hand: it constitutes a promising way forward for the philosophy of pleasure. 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