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In philosophy of mind, qualia (; singular: quale ) are defined as instances of Subjectivity, consciousness. The term qualia derives from the Latin neuter plural form ( qualia) of the Latin adjective quālis () meaning "of what sort" or "of what kind" in relation to a specific instance, such as "what it is like to taste a specific this particular apple now".
Examples of qualia include the perceived sensation of pain of a headache, the taste of wine, and the redness of an evening sky. As qualitative characteristics of sensations, qualia stand in contrast to propositional attitudes, where the focus is on beliefs about experience rather than what it is directly like to be experiencing.
C.S. Peirce introduced the term quale in philosophy in 1866, and in 1929 C. I. Lewis was the first to use the term "qualia" in its generally agreed-upon modern sense. Frank Jackson later defined qualia as "...certain features of the bodily sensations especially, but also of certain perceptual experiences, which no amount of purely physical information includes". Philosopher and cognitive scientist Daniel Dennett suggested that qualia was "an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us".
The nature and existence of qualia under various definitions remain controversial. Much of the debate over the importance of qualia hinges on the definition of the term, and various philosophers emphasize or deny the existence of certain features of qualia. Some philosophers of mind, like Daniel Dennett, argue that qualia do not exist. Other philosophers, as well as neuroscientists and neurologists, believe qualia exist and that the desire by some philosophers to disregard qualia is based on an erroneous interpretation of what constitutes science.
Leibniz's passage in his Monadology in 1714 described the explanatory gap as follows:
It must be confessed, moreover, that perception, and that which depends on it, are inexplicable by mechanical causes, that is, by figures and motions. And, supposing that there were a mechanism so constructed as to think, feel and have perception, we might enter it as into a mill. And this granted, we should only find on visiting it, pieces which push one against another, but never anything by which to explain a perception. This must be sought, therefore, in the simple substance, and not in the composite or in the machine.
Charles Sanders Peirce introduced the term quale in philosophy in 1866, and in 1929 C.I. Lewis was the first to use the term "qualia" in its generally agreed upon modern sense.
Frank Jackson later defined qualia as "...certain features of the bodily sensations especially, but also of certain perceptual experiences, which no amount of purely physical information includes".
Daniel Dennett suggested that qualia was "an unfamiliar term for something that could not be more familiar to each of us: the ways things seem to us". He identifies four properties that are commonly ascribed to qualia. According to these, qualia are:
If qualia of this sort exist, then a normally sighted person who sees red would be unable to describe the experience of this perception in such a way that a listener who has never experienced color will be able to know everything there is to know about that experience. Though it is possible to make an analogy, such as "red looks hot", or to provide a description of the conditions under which the experience occurs, such as "it's the color you see when light of 700-nanometer wavelength is directed at you", supporters of this definition of qualia contend that such descriptions cannot provide a complete description of the experience.
Another way of defining qualia is as "raw feels". A raw feel is a perception in and of itself, considered entirely in isolation from any effect it might have on behavior and behavioral disposition. In contrast, a cooked feel is that perception seen in terms of its effects. For example, the perception of the taste of wine is an ineffable, raw feel, while the behavioral reaction one has to the warmth or bitterness caused by that taste of wine would be a cooked feel. Cooked feels are not qualia.
Arguably, the idea of hedonistic utilitarianism, where the ethical value of things is determined from the amount of subjective pleasure or pain they cause, is dependent on the existence of qualia.
The idea that an inverted spectrum would be undetectable in practice is also open to criticism on more scientific grounds, by C. L. Hardin, among others. As Alex Byrne puts it:
According to David Chalmers, all "functionally isomorphic" systems (those with the same "fine-grained functional organization", i.e., the same information processing) will have qualitatively identical conscious experiences. He calls this the principle of organizational invariance. For example, it implies that a silicon chip that is functionally isomorphic to a brain will have the same perception of the color red, given the same sensory inputs. He proposed the thought experiment of the "dancing qualia" to demonstrate this. It is a reductio ad absurdum argument that starts by supposing that two such systems can have different qualia in the same situation. It involves a switch that enables connecting the main part of the brain with either of these two subsystems. For example, one subsystem could be a chunk of brain that causes an object to appear red, and the other could be a silicon chip that causes the object to appear blue. Since both perform the same function within the brain, the subject would be unable to notice any change during the switch. Chalmers argues that this would be highly implausible if the qualia were truly switching between red and blue, hence the contradiction. Therefore, he concludes that the dancing qualia is impossible in practice, and the functionally isomorphic digital system would not only experience qualia, but it would have conscious experiences that are qualitatively identical to those of the biological system (e.g., seeing the same color). He also proposed a similar thought experiment, named the fading qualia, that argues that it is not possible for the qualia to fade when each biological neuron is replaced by a functional equivalent.
The argument holds that it is conceivable for a person to have a duplicate, identical in every physical way, but lacking consciousness, called a "philosophical zombie." It would appear exactly the same as the original person, in both behavior and speech, just without subjective phenomenology. For these zombies to exist, qualia must not arise from any specific part or parts of the brain, for if it did there would be no difference between "normal humans" and philosophical zombies: The zombie/normal-human distinction can only be valid if subjective consciousness is separate from the physical brain.
According to Chalmers, the simplest form of the argument goes as follows:
Former AI researcher Marvin Minsky sees the argument as circular. He says the proposition of something physically identical to a human but without subjective experience assumes that the physical characteristics of humans cannot produce consciousness, which is exactly what the argument claims to prove. In other words, it tries to prove consciousness is nonphysical by assuming consciousness is nonphysical.
However, such an epistemological or explanatory problem might indicate an underlying metaphysical issue, as even if not proven by conceivability arguments, the non-physicality of qualia is far from ruled out.
Jackson claimed that she does.
This thought experiment has two purposes. First, it is intended to show that qualia exist. If we accept the thought experiment, we believe that upon leaving the room Mary gains something: the knowledge of a particular thing that she did not possess before. That knowledge, Jackson argues, is knowledge of the quale that corresponds to the experience of seeing red, and it must thus be conceded that qualia are real properties, since there is a difference between a person who has access to a particular quale and one who does not.
The second purpose of this argument is to refute the physicalist account of the mind. Specifically, the knowledge argument is an attack on the physicalist claim about the completeness of physical truths. The challenge posed to physicalism by the knowledge argument runs as follows:
Early in his career Jackson argued that qualia are epiphenomenalism, meaning they have no causal influence on the physical world. The issue with this view is that if qualia are non-physical, it becomes unclear how they can have any effect on the brain or behavior. Jackson later rejected epiphenomenalism, arguing that knowledge about qualia is impossible if they are epiphenomenal. He concluded that there must be an issue with the knowledge argument, eventually embracing a representationalist account, arguing that sensory experiences can be understood in physical terms.
Maund extended his argument with reference to color. Color he sees as a dispositional property, not an objective one. Colors are "virtual properties", which means they are as if things possessed them. Although the naïve view attributes them to objects, they are intrinsic, non-relational, inner experiences. This allows for the different perceptions between person and person, and also leaves aside the claim that external objects are colored.
Similarly, William Robinson, in Understanding Phenomenal Consciousness, (2025). 9780521834636, Cambridge University Press. ISBN 9780521834636 advocates for dualism and rejects the idea of reducing phenomenal experience to neural processes. His theory of Qualitative Event Realism proposes that phenomenal consciousness consists of immaterial events caused by brain activity but not reducible to it. He seeks to conciliate dualism with scientific methodology, aiming for a future unified theory that respects both phenomenal qualities and scientific explanations.
Damasio points out that "in all likelihood, I will never know your thoughts unless you tell me, and you will never know mine until I tell you." The reason he gives for this is that "the mind and its consciousness are first and foremost private phenomena" that are personal, private experiences that should be investigated as such. While he believes that trying to study these experiences "by the study of their behavioral correlates is wrong," he does think they can be studied as "the idea that subjective experiences are not scientifically accessible is nonsense." In his view the way to do this is for "enough observers to undertake rigorous observations according to the same experimental design; and ... that those observations be checked for consistency across observers and that they yield some form of measurement." He also thinks that "subjective observations ... can inspire objective experiments" and "be explained in terms of the available scientific knowledge".
In his mind:
Llinás contends that qualia are a product of neuronal oscillation and cites anesthesia experiments, showing that qualia can be "turned off" by altering brain oscillations while other connections remain intact.
These authors approach qualia from an empirical perspective and not as a logical or philosophical problem. They wonder how qualia evolved, and in doing so consider a skeptical point of view in which, since the objective scientific description of the world is complete without qualia, it is nonsense to ask why they evolved or what they are for. However they decide against this skeptical view.
Based on the parsimony principle of Occam's razor, one could accept epiphenomenalism and deny qualia, since they are not necessary for a description of the functioning of the brain. However, they argue that Occam's razor is not useful for scientific discovery. For example, the discovery of relativity in physics was not the product of accepting Occam's razor but rather of rejecting it and asking the question of whether a deeper generalization, not required by the currently available data, was true and would allow for unexpected predictions. Most scientific discoveries arise, these authors argue, from ontologically promiscuous conjectures that do not come from current data.
The authors then point out that skepticism might be justified in the philosophical field, but that science is the wrong place for skepticism, such as asking if "your red is not my green" or if we can be logically certain that we are not dreaming. Science, these authors assert, deals with what is probably true, beyond reasonable doubt, not with what can be known with complete and absolute certainty. The authors say that most neuroscientists and even most psychologists dispute the very existence of the problem of qualia.
In Dennett's updated version of the inverted spectrum thought experiment, which he calls alternative neurosurgery, you again awake to find that your qualia have been inverted – grass appears red, the sky appears orange, etc. According to the original account, you should be immediately aware that something has gone horribly wrong. Dennett argues, however, that it is impossible to know whether the diabolical neurosurgeons have indeed inverted your qualia (e.g. by tampering with your optic nerve), or have simply inverted your connection to memories of past qualia. Since both operations would produce the same result, you would have no means on your own to tell which operation has actually been conducted, and you are thus in the odd position of not knowing whether there has been a change in your "immediately apprehensible" qualia.
Dennett argues that for qualia to be taken seriously as a component of experience – for them to make sense as a discrete concept – it must be possible to show that:
Dennett attempts to show that we cannot satisfy (a) either through introspection or through observation, and that qualia's very definition undermines its chances of satisfying (b).
Supporters of qualia point out that in order for you to notice a change in qualia, you must compare your current qualia with your memories of past qualia. Arguably, such a comparison would involve immediate assessment of your current qualia and your memories of past qualia, but not of the past qualia themselves. Furthermore, modern functional brain imaging has increasingly suggested that the memory of an experience is processed in similar ways, and in similar zones of the brain, as the original perception.
This may mean that there would be asymmetric outcomes between altering the mechanism of perception of qualia and altering the memory of that qualia. If the diabolical neurosurgery altered the immediate perception of qualia, the inversion might not be noticed directly, since the brain zones which re-process the memories would invert the remembered qualia. On the other hand, alteration of the qualia memories themselves would be processed without inversion, and thus you would perceive them as an inversion. Thus, you might know immediately if memory of your qualia had been altered, but might not know if immediate qualia were inverted or whether the diabolical neurosurgeons had done a sham procedure.
Dennett responds to the Mary the color scientist thought experiment by arguing that Mary would not, in fact, learn something new if she stepped out of her black and white room to see the color red. Dennett asserts that if she already truly knew "everything about color", that knowledge would include a deep understanding of why and how human neurology causes us to sense the quale of color. Mary would therefore already know exactly what to expect upon seeing red, before ever leaving the room.
Dennett argues that the misleading aspect of the story is that Mary is supposed to not merely be knowledgeable about color but to actually know all the physical facts about it, which would be a knowledge so deep that it exceeds what can be imagined, and twists our intuitions. If Mary really does know everything physical there is to know about the experience of color, then this effectively grants her almost omniscient powers of knowledge. Using this, she will be able to deduce her own reaction, and figure out exactly what the experience of seeing red will feel like.
Dennett finds that many people find it difficult to see this, so he uses the case of RoboMary to further illustrate what it would be like for Mary to possess such a vast knowledge of the physical workings of the human brain and color vision. RoboMary is an intelligent robot who, instead of having color cameras as eyes, has a software lock such that they are only able to perceive black and white and shades in-between.
RoboMary can examine the computer brain of similar non-color-locked robots when they see red, and see exactly how they react and what kinds of impulses occur. RoboMary can also construct a simulation of her own brain, unlock the simulation's color-lock and, with reference to the other robots, simulate exactly how this simulation of herself reacts to seeing red. RoboMary naturally has control over all of her internal states except for the color-lock. With the knowledge of her simulation's internal states upon seeing red, RoboMary can put her own internal states directly into the states they would be in upon seeing red. In this way, without ever actually seeing red through her cameras, she will know exactly what it is like to see red.
Dennett uses this example as an attempt to show us that Mary's all-encompassing physical knowledge makes her own internal states as transparent as those of a robot or computer, and it is as straightforward for her to figure out exactly how it feels to see red.
Perhaps Mary's failure to learn exactly what seeing red feels like is simply a failure of language, or a failure of our ability to describe experiences. An alien race with a different method of communication or description might be perfectly able to teach their version of Mary exactly how seeing the color red would feel. Perhaps it is simply a uniquely human failing to communicate first-person experiences from a third-person perspective. Dennett suggests that the description might even be possible using English. He uses a simpler version of the Mary thought experiment to show how this might work. What if Mary was in a room without triangles and was prevented from seeing or making any triangles? An English-language description of just a few words would be sufficient for her to imagine what it is like to see a triangle – she can simply and directly visualize a triangle in her mind. Similarly, Dennett proposes, it is perfectly, logically, possible that the quale of what it is like to see red could eventually be described in an English-language description of millions or billions of words.
In Are we explaining consciousness yet?, Dennett approves of an account of qualia defined as the deep, rich collection of individual neural responses that are too fine-grained for language to capture. For instance, a person might have an alarming reaction to yellow because of a yellow car that hit her previously, and someone else might have a nostalgic reaction to a comfort food. These effects are too individual-specific to be captured by English words. "If one dubs this inevitable residue qualia, then qualia are guaranteed to exist, but they are just more of the same, dispositional properties that have not yet been entered in the catalog".
Lewis states that Jackson's thought experiment uses the phenomenal information hypothesis – that is, that the new knowledge that Mary gains upon seeing red is Phenomenalism information. Lewis then proposes a different ability hypothesis that differentiates between two types of knowledge: knowledge "that" ( information) and knowledge "how" ( abilities). Normally the two are entangled; ordinary learning is also an experience of the subject concerned, and people learn both information (for instance, that Freud was a psychologist) and gain ability (to recognize images of Freud). However, in the thought experiment, Mary can use ordinary learning only to gain "that" knowledge. She is prevented from using experience to gain the "how" knowledge that would allow her to remember, imagine and recognize the color red.
We have the intuition that Mary has been deprived of some vital data to do with the experience of redness. It is also uncontroversial that some things cannot be learned inside the room; for example, Mary cannot learn how to ski within the room. Lewis has articulated that information and ability are potentially different things. In this way, physicalism is still compatible with the conclusion that Mary gains new knowledge. It is also useful for considering other instances of qualia – "being a bat" is an ability, so it is "how" knowledge. (2025). 9780262621892, the MIT press. ISBN 9780262621892
Physicalism follows. Although Papineau recognises that it is possible to reject these premisses, he claims that to do so leads to empirically implausible conclusions.
Papineau’s book The Metaphysics of Sensory Experience has been critiqued by philosopher Benj Hellie. Hellie instead argues in favor of a theory with the existence of qualia, and that all alternatives to qualia fail.
In attempting to answer the question "why is the phenomenal immaterial?", he notes that there is nothing to suggest that the phenomenal and the physical are anything more than two different ways of talking about the states or properties of people. Even if the appearance/reality distinction does not exist for phenomenal properties, the fact that self-attributions of such properties are typically considered incorrigible could simply reflect an epistemic distinction or a linguistic convention. If this is the case, then Rorty claims that the problem of consciousness is not actually a real metaphysical problem:
"The purportedly metaphysical "problem of consciousness" is no more and no less than the epistemological "problem of privileged access," and that once this is seen questions about dualism versus materialism lose their interest."
Rorty suggests that the only answer that one can give as to why qualia are ontologically distinct from physical processes is that the lack of an appearance/reality distinction is an essential feature of their being (i.e. it is an essential feature of a quale that it be incorrigibly known), but he notes that in making this move, qualia have been hypostatized such that they can take on the property of being pure appearances. In other words, they have been turned into non-physical, property-bearing particulars, meaning they are no longer properties of the person who has them, but rather particulars that exist in addition to that person. Thus, the intuition that the physical facts do not entail the phenomenal facts is simply the intuition that the universal pain quale does not exist anywhere in a world of particular pains which instantiate it:
"The neo-dualist who identifies a pain with how it feels to be in pain is hypostatizing a property—painfulness—into a special sort of particular, a particular of that sort whose esse is percipi and whose reality is exhausted in our initial acquaintance with it. The neo-dualist is no longer talking about how people feel but about feelings as little self-subsistent entities, floating free of people in the way in which universals float free of the instantiations."
He thus criticizes philosophers who accuse materialists of not taking qualia seriously when they talk about the neural workings of the brain:
"Thus when neo-dualists say that how pains feel are essential to what pains are, and then criticize Smart for thinking of the causal role of certain neurons as what is essential to pain, they are changing the subject. Smart is talking about what is essential to people being in pain, whereas neo-dualists like Saul Kripke are talking about what is essential for something's being a pain."
In his book On Human Nature, Scruton poses a potential line of criticism to this, which is that while Wittgenstein's private language argument does disprove the concept of reference to qualia, or the idea that we can talk, even to ourselves, of their nature; it does not disprove their existence altogether. Scruton believes that this is a valid criticism, and this is why he stops short of actually saying that qualia do not exist, and instead merely suggests that we should abandon the concept. However, he quotes Wittgenstein in response: "Whereof one cannot speak, thereof one must be silent."
From this he concludes "that there are no such qualities of experiences. They are qualities of external surfaces (and volumes and films), if they are qualities of anything." Thus he believes we can take our experiences at face value since there is no fear of losing contact with the realness of physical objects.
In Tye's thought there is no question of qualia without information being contained within them; it is always "an awareness that" and always "representational". He characterizes the perception of children as a misperception of referents that are undoubtedly as present for them as they are for grown-ups. As he puts it, they may not know that "the house is dilapidated", but there is no doubt about their seeing the house. After-images are dismissed as presenting no problem for the transparency theory because, as he puts it, after-images being illusory, there is nothing that one sees.
Tye proposes that phenomenal experience has five basic elements, for which he has coined the acronym PANIC – Poised, Abstract, Nonconceptual, Intentional Content.
Tye adds that the experience is like a map in that, in most cases, it goes beyond the shapes, edges, volumes, etc. in the world – you may not be reading the a map but, as with an actual map there is a reliable match with what it is mapping. This is why Tye calls his theory representationalism, makes it plain that Tye believes that he has retained a direct contact with what produces the phenomena and is therefore not hampered by any trace of a "veil of perception".
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