Loosely defined, the term “qualia” usually refers to the phenomenal aspects of mental experience. Examples from the Stanford Encyclopedia of Philosophy should suffice: “I run my fingers over sandpaper, smell a skunk, feel a sharp pain in my finger, seem to see bright purple, become extremely angry” (Tye, “Qualia”). To undergo any of these experiences, most of us would agree, would entail a very particular feeling. Quite apart from the simple recognition of damage from sandpaper, or the mere identification of a particularly bright shade of purple, there seems to be a qualitative – phenomenal – aspect to each of these mental affairs. Simply put, there is something it is like for you or me to have an experience. Thomas Nagel, Keith Campbell, and Frank Jackson each argue that qualia, in this broad sense, must exist (Nagel, “What Is It Like To Be A Bat?”; Campbell, “A Critique of Central-State Materialism”; Jackson, “Epiphenomenal Qualia”).

However, exactly what “qualia” means to each thinker differs substantially, and the conclusions they draw vary accordingly. Nagel’s analysis allows for qualia to be essentially physical properties of a purely physical realm of the mind and to play a causal role in the physical events of the universe; thus, his analysis of qualia poses no threat to the physicalist doctrine that everything is physical (Stoljar, “Physicalism”). Campbell and Jackson deny that qualia are physical; thus, their analyses of qualia seek to falsify the physicalist premise. This paper contends that Campbell’s and Jackson’s analyses carry no ontological weight, rely on a primary intuition with unclear origins, and lead to highly counterintuitive and worrying consequences. Nagel’s analysis, in contrast, necessitates none of the suspect results that come with Campbell’s and Jackson’s claims. Consequently, we should take Nagel’s account of qualia – which does not show physicalism to be mistaken – to be overwhelmingly preferable.

Nagel approaches the question of qualia by examining what he terms “the subjective character of experience” (323). He clarifies exactly what he means when referring to this subjective element by inviting us to imagine what it would be like to be a different form of life. A bat’s experience when it uses sonar to sense the world, for example, must be completely dissimilar to anything that a human can experience (Nagel 324). Though we may imagine what it would be like “to behave as a bat behaves,” Nagel argues, we cannot imagine what it is like to be this organism (324). Furthermore, it seems to Nagel that physical science as it stands today cannot help us understand what it is like to be something that we are not. A bat’s qualia – Nagel’s what-it-is-likeness – are completely inaccessible to humans through any third-person analysis because their inherently subjective element would necessarily be lost through any objective inquiry (Nagel 323, 326).

Though Nagel admits that we might never be able to experience a bat’s qualia, he sees no reason to deny that there is nonetheless a fact of the matter. Human conception and the lack thereof, he believes, have no implication to what is real. Indeed, Nagel argues that “to deny that the reality or logical significance of what we can never describe or understand is the crudest form of cognitive dissonance” (325). This subjective realism is crucial to his analysis: it allows him to treat the problem he raises as an epistemic one, with no ontological commitments attached. Facts presently unintelligible through objective physical analysis need not be non-physical. Indeed, qualia could yet be physical in spite of the fact that “we have at present no conception of what an explanation of the physical nature of a mental phenomenon would be” (Nagel 322). Accordingly, Nagel refuses to denounce the physicalist position that everything, including qualia, is physical (328).

In contrast, Campbell’s account of qualia entails exactly what Nagel refuses to commit to, that physicalism is false. This follows from his claim that “the enjoying or enduring of phenomenal properties is not a physical affair” (Campbell 338). Because Campbell’s phenomenal properties – qualia – are non-physical, Campbell’s analysis stands in stark opposition the belief that everything is physical; physicalism, to Campbell, must be mistaken. To support this view, Campbell presents us with a critique of the Causal Theory of mind. This widely-accepted theory holds that inner mental states cause our outward behaviour (Campbell 333). For example, in the case that my finger is burned, the Causal Theory holds that certain “components” arise in my mental state: these include “awareness” that my finger is burned and “desire” that this awareness stop immediately (Campbell 333). Mental components such as these combine to form a causal chain that results in my behaviour: for example, I might decide to run my finger under cold water. Campbell agrees with the Causal Theory that these mental components are entirely physical, writing that “the brain’s activities of a physical kind all occur in accordance with physical laws” (337). Because of their physical nature and their functional role in determining behaviour, we may call these mental components “physical-functional properties.”

Campbell argues that the Causal Theory, though perfectly adequate in explaining behaviour by appealing to physical-functional properties of the mental realm, is nonetheless incomplete. Nowhere in the Causal Theory, he argues, is there room for qualia; “the hurtfulness of pain must lie elsewhere” (Campbell 334). To help understand why this must be so, Campbell asks us to imagine a person who has all of the same physical-functional properties as you or I, but yet lacks any “phenomenal properties”, any qualitative aspects of experience (333-335). This “Imitation Man” would be completely physically indistinguishable from a normal person: we could apply the Causal Theory to his behaviour with stunning success, and we could even – scientific progress permitting – examine the physical-functional aspects of his mental states (Campbell 334). Because Imitation Man has no phenomenal properties but remains physically identical to a normal person in every respect, these phenomenal properties must be non-physical. For this reason, Campbell places himself in the New Epiphenomenalist camp, which holds that qualia are both non-physical and non-causal (337-338).

Of course, a physicalist with inclinations towards Nagel’s view of qualia might reply that Imitation Man proves nothing: though we may use Imitation Man to conceptually divorce phenomenal properties (qualia) from physical-functional properties, Campbell does not show why this must be the case. Qualia could just be one and the same as physical-functional properties; indeed, Nagel does not deny that qualia have a causal role in behaviour (323). With Imitation Man, Campbell merely suggests the presence of non-physical qualia in addition to physical-functional properties, and shows how it would follow that physicalism would be mistaken. Thus, the physicalist might argue, Campbell has only shown it to be conceptually possible that physicalism could be false; he has not proven it wrong in any serious sense.

However, according to a popular understanding of physicalism, the physicalist is wrong to draw the above conclusion. The view that everything is physical is usually interpreted to mean that it is impossible for there to be non-physical things (Kirk, “Zombies”). Thus, if Campbell can prove that it is even possible that Imitation Man could exist – and that, by extension, phenomenal properties need not be physical – then he proves physicalism false. In short, if physicalism holds that there cannot be non-physical properties and Imitation Man shows that there could be non-physical properties, physicalism is wrong.

Before accepting the Imitation Man argument wholesale, however, we must examine whether or not he is conceptually possible. Though Campbell seems to take this to be intuitively obvious, Jackson – also an epiphenomenalist – points out that some philosophers “sincerely deny that there can be physical replicas of us in other possible worlds which nevertheless lack consciousness” (Jackson 343). Indeed, in order for Imitation Man to be possible, he must not break any laws of physics. Epiphenomenalists agree that it would be impossible for a non-physical entity to cause a physical event, so Imitation Man’s non-physical properties must by definition be non-causal. Epiphenomenalists must therefore show that qualia could be non-causal before we may allow that Imitation Man is even conceptually possible. But the non-causal nature of qualia is exactly what Imitation Man is designed to prove! In this important respect, Imitation Man begs the question; we cannot accept his conceptual existence unless epiphenomenalists provide some reason to do so.

Perhaps it is well and good that we cannot accept Campbell’s mode of reasoning, for it can lead to highly counterintuitive claims. Consider the following thought experiment.1 Torture Man is just like me in every physical respect, but his qualitative experience is rather different from mine. When he smells a rose, Torture Man experiences exactly the same qualia that I would experience if I were exposed to mustard gas; when Torture Man steps outside, the cool breeze on his skin feels much the same way that a swim in boiling water would feel for me. Every aspect of Torture Man’s pitiful existence is horrifyingly awful in a phenomenological sense until the day he dies, but he cannot do anything about it – nor could he want to – because he is physical-functionally normal. In fact, to accept Campbell’s framework is to accept that you, the reader of this essay, could be a Torture Man or a Torture Woman, and that, because qualia have no causal role, you would have no way of knowing if you were being tortured at this very moment. This seems at first to be a terrifying prospect. However, consider what the term “torture” would entail if you had no knowledge – before, during, or after the fact – that it was happening. The term would be meaningless. Though the definition of “torture” seems inherently to require that the victim at least realize that it has occurred, Campbell’s account of qualia would require us to deny even this. In addition to presupposing what it is designed to prove, Campbell’s conceptual framework can lead to extremely counterintuitive results.

Jackson’s account of qualia is troubled by neither of these problems. His thought experiment2 does not presuppose the existence of non-physical qualia but, rather, attempts to pick them out of something he believes to be a feasible state of affairs. Jackson introduces us to Mary, a gifted scientist specializing in colour. Mary conducts all of her research from a black and white room with a monochrome television – indeed she has never seen colour – and, because she is so brilliant, proceeds to learn “all the physical information” about colour (Jackson 342). Having discovered every physical fact there is to know related to her field, Mary decides to take a stroll outside her room, so she steps outside and sees colour for the first time. Jackson argues that when Mary does this, it “seems just obvious that she will learn something about the world and our visual experience of it” (342). Clearly, Jackson reasons, Mary’s previous knowledge was incomplete, even though it included every physical fact. Jackson tells us specifically that “qualia are left out of the physicalist story” and, consequently, physicalism is false (342).

Recall that as an epiphenomenalist Jackson holds that these qualia are not only non-physical but, crucially, non-causal: their “possession or absence makes no difference to the physical world” (344). Though Jackson holds that Mary “will learn something” when she sees colour, his epiphenomenalist definition of qualia commits him to the belief that qualia could not be the cause of this learning. If qualia were the cause, then Mary’s learning could not have any effects on the physical world; learning could not even be a physical aspect of the mental. Indeed, Campbell recognizes essentially this point when he admits that “the experience of the quality in question [qualia] is inoperative in behaviour, even the behaviour in which such experiences [qualia] are described” (337). In short, if non-physical qualia were the cause of what Mary learned, then she could never show it, nor could she even know that she had learned it. This does not seem to be the sense in which we intuitively attribute learning to Mary.

Given that it seems intuitive that a proper understanding of learning should involve its ability to lead to behaviour, then Mary’s learning was not caused by qualia. Instead, it must have been caused by something physical, for it could not have simply popped into existence. However, if this is the case, then Jackson did not tell us the whole story when he argued that qualia were left out of the physicalist story (342): indeed, something physical was left out as well! It appears strangely paradoxical that the physicalist story could leave out something physical, but this is what Jackson’s epiphenomenalist views seem to entail. To avoid this contradiction, we could reject Jackson’s premise that Mary knew every piece of information before she stepped into the world of colour, if we are to accept what he sees as “just obvious”, that she learned something new (342). Interestingly, Nagel’s account of qualia allows for exactly this possibility. Just as, Nagel admits, there might be physical facts about what it is like to be a bat “beyond the reach of human concepts” (325), so too there might be facts about colour that Mary could not have grasped through a purely objective analysis. If, as Nagel suggests, the physical world is not fully describable in objective terms, then Mary could never have been as brilliantly knowledgeable as Jackson supposes. By Nagel’s account, we cannot accept Jackson’s premise that Mary knew “all the physical information” (342). In attempting to escape Campbell’s method of presupposition, Jackson falls prey to a troublesome premise of his own.

The intuition upon which Campbell and Jackson base their epiphenomenalist claim that qualia must be non-physical forces them to argue that qualia are also non-causal, leading to serious problems: the Imitation Man thought experiment, in order to be conceptually possible, requires Campbell to presuppose what it is designed to prove, while Jackson stipulates that Mary must know what she cannot. In addition, the epiphenomenalist intuition requires that we accept highly counterintuitive definitions of words like “torture” and “learning”. These arguments cast considerable doubt on Campbell’s and Jackson’s mutual conclusion that physicalism is false. Nagel’s analysis, in contrast, is less problematic. It allows qualia to be physical and causal while suffering none of the weaknesses that plague Campbell’s and Jackson’s arguments. Nagel cannot presume, nor can we, that physicalism is mistaken.