Deviant Phenomenal Knowledge
Phenomenal knowledge is normally defined as "knowing what it is like to experience [something]". This is usually further defined either in terms of, or in terms closely related to, the abilities to recognize, remember, and imagine experiences. Some recent philosophical discussions have focused on the issue of deviant phenomenal knowledge. Torin Alter (2008) explains:
Phenomenal knowledge is earned if the experience requirement is satisfied. For example, since I have seen ripe tomatoes, my knowledge of what it’s like to see red is earned . . . To access phenomenal knowledge is to exercise closely related abilities, such as the ability to imagine, recognize, or remember relevant experiences. I access my phenomenal knowledge when I visualize a ripe tomato, stop at a traffic light, or have an episodic memory of seeing oxygenated blood. Phenomenal knowledge that is unearned, inaccessible, or both is deviant.
In what follows, I use "deviant" to refer to anybody who has deviant phenomenal knowledge. If deviants are possible, then it is possible for a person to know what it is like to see the color red without ever having seen, imagined, or hallucinated the color red. Discussions of deviants have focused on whether or not they create a problem for the knowledge argument against physicalism (Alter, 2008; Dennett, 2007; Mandik, 2010). However, I do not wish to discuss the knowledge argument here, nor do I want to discuss whether or not deviants cause a problem for anti-physicalists. Rather, I want to argue that the notion of a deviant is not obviously coherent, and that deviants are plausibly impossible. If the notion of a deviant is coherent, then the possibility of deviants remains an empirical question. Furthermore, I argue that the burden is on the supporters of deviants to substantiate their claim that deviants are both conceivable and possible.
Under some definitions of "phenomenal knowledge," the possibility of a deviant may be rejected a priori. According to the ability hypothesis, for example, phenomenal knowledge is defined as the abilities to recognize, imagine, and remember an experience (Churchland, 1989; Lewis, 1988; Nemirow, 1990, 2006). Yet, deviants cannot have true memories of the experiences they are supposed to have knowledge of. A deviant may think they are accessing memories of past experiences, but they are wrong. They are merely imagining experiences and wrongly judging them to be memories. Thus, the deviant does not have all of the right abilities, and so does not have the requisite phenomenal knowledge. In short, the deviant is not a deviant at all. According to the ability hypothesis, then, the notion of deviant phenomenal knowledge is self-contradictory.
Of course, the ability hypothesis is not universally lauded. Those who reject the ability hypothesis might suppose that phenomenal knowledge does not require the possession of true memories. Some might suppose that no memories are required at all, while others might claim that a deviant could have implanted memories which, though false in the strict sense, might still satisfy the requirement of phenomenal knowledge. Though I do not find either of these alternatives compelling (I am a supporter of the ability hypothesis), I will--for the sake of argument--accept that true memories are not required for phenomenal knowledge, and on that basis consider whether or not deviants are possible.
One way of approaching this topic is to consider Swampkinds. Davidson (1987) introduces the idea:
Suppose lightning strikes a dead tree in a swamp; I am standing nearby. My body is reduced to its elements, while entirely by coincidence (and out of different molecules) the tree is turned into my physical replica. My replica, The Swampman.....moves into my house and seems to write articles on radical interpretation. No one can tell the difference.
Enter Swamp Mary, a Swamp-version of Mary the super-scientist. Mary, as you may recall, learns all about color vision while confined to a black-and-white existence. Then she steps out of her room and sees a red tomato for the first time. Now she knows what it is like to see red. She earned it. A moment later, lightning strikes and Swamp Mary is born. Swamp Mary has access to the same knowledge Mary had, and so she should know what it is like to see a red tomato. Yet, Swamp Mary hasn't earned that knowledge. Her history does not include an experience of phenomenal redness. Swamp Mary is thus said to be a deviant (Alter, 2008; Dennett, 2007; Mandik, 2010).
(In Dennett's version, Swamp Mary is born before Mary ever sees a red tomato: the lightning strikes Mary and reconfigures her brain so that she is in the exact state she would have been in had she experienced the sight of a red tomato. The result is the same: lightning produces a Swamp version of Mary who supposedly knows what it is like to see red without ever having seen red.)
Whether Swamp Mary is possible depends partly on what it would take to create her. Millikan (1996) observes that there are limitations on the ways a Swamp person can come into existence. Biological science tells us:
You can't in principle build large organic molecules such as hemoglobin, they say, just by throwing the right amino acid molecules together at the right angles with the right energies and having them stick. . . Molecules like that must be built up through long chains of enzymatic cascading reactions that proceed in just the right order and require support from just the right helping catalysts timed to come on stage at just the right moments.
Thus, one way for a Swamp person to come about is through a long and complex biological process. However, this is not how Swampkinds are usually imagined. They are supposed to be born out of a sudden jolt of creative energy. (Lightning is often involved, perhaps for dramatic flair.) Is there another, more spontaneous way for Swamp people to come into being?
Millikan says yes, there is a way. First, she reminds us that the laws of physics are time-symmetric. What can happen going forward in time can also happen in reverse. So, if a person can be disintegrated into tiny particles--blown to bits, as it were--then a Swamp person can be reintegrated in exactly the same manner. Yet, as Millikan notes, such a Swamp person would live backwards in time:
A Swampman so originated will himself be running backwards when he has been formed. His cells will be getting younger rather than older, coalescing rather than dividing, returning nutrients to his blood which will run backwards, returning the nutrients to his digestive system from whence they will eventually emerge as new good hamburgers getting fresher by the moment.
I'm skipping over some of the details of Millikan's analysis, but the point is clear enough. If Swamp Mary is going to happen in this world (or a world reasonably similar to this one), then it can only happen in conformity with the laws of physics, and this places constraints on how she can be created. It is most likely that Swamp Mary can only come about via a long and complex biological process, the full details of which are as yet unknown.
Supposing that Swamp Mary is possible, there is also the question of whether or not she really is a deviant. We cannot assume she is. For example, Millikan (1996) argues that we cannot attribute beliefs or other intentional states to Swampkinds, and this would preclude any knowledge attributions. She quotes a point made in her (1984):
Suppose that by some cosmic accident a collection of molecules formerly in random motion were to coalesce to form your exact physical double. ...that being would have no ideas, no beliefs, no intentions, no aspirations, no fears, and no hopes....This because the evolutionary history of the being would be wrong.
Davidson (1987) makes a similar point, though instead of appealing to the lack of evolutionary history, he appeals to the lack of individual history, writing: "I don't see how my replica can be said to mean anything by the sounds it makes, nor to have any thoughts."
The Davidson-Millikan objection is that, because Swampkinds lack the right histories (be they individual, evolutionary, or both), we cannot treat them like human beings. They cannot be deviants. I do not know how much weight is given to this argument in the literature, but it does appear to be a coherent objection. This makes the appeal to Swampkinds somewhat more difficult. [Update: see here for more on this line of thought].
In any case, all of the deviant eggs are not in the Swamp basket. Alter (2008) mentions other seemingly plausible ways of creating a deviant:
Unger imagines that scientists construct a man who is “cell‐part for cell‐part, cell for cell, nervous structure for nervous structure identical to” a man who both knows what it’s like to see red and has come upon this knowledge the ordinary way (Unger 1966: 50). Others (e.g., Lewis 1988, Alter 1998, Stoljar 2005) imagine cases in which surgeons operate on a person who has never seen red, creating brain structures similar to those found in the brains of people who have seen red.
In all of these cases, including Swamp Mary, the alleged deviant requires some long, elaborate, and neurologically complex process in order to produce their phenomenal knowledge. Yet, such processes cannot entail an experience of phenomenal redness--or any other experience which could earn phenomenal knowledge of redness, such as experiences which are simpler than experiences of phenomenal redness and out of which experiences of phenomenal redness might be composed.
(There may be disagreement about whether an experience of phenomenal redness is simple or complex. I will not argue one way or the other here. However, I think all sides agree that some experiences are composed of smaller or more primitive experiential components. Presumably, if one earns phenomenal knowledge of the more primitive components, one has earned phenomenal knowledge of the composites.)
Alter, Dennett, and Mandik are willing to assume that deviants could be constructed and function without ever experiencing even a hallucination of the color red. I find that remarkable, since there is no consensus about what sorts of physiological processes are necessary or sufficient for phenomenal consciousness. Any consensus can only be reached by appeal to the empirical sciences, and this makes the possibility of deviants an empirical question. I am inclined to think that deviants are impossible, though I admit that evidence could prove me wrong.
My thesis is thus: A person cannot be put into a functional state of knowing what it is like to see red without being put in experiential states which earn that knowledge. My intuition is that the elaborate process of constructing the right neurological configurations, or the very having of those configurations in a functionally operative state, necessarily entails perceptual experiences which are sufficient to earn all of their phenomenal knowledge. Of course, not being able to explain how such configurations can be constructed, I do not expect my intuition to be compelling to anybody. However, compelling or not, I do think this view is plausible. Furthermore, I think the burden of proof is on the people who disagree with me.
Here is my argument. We might define an "earning experience" as any local, biological process capable of producing the right synaptic configuration. In such a case, deviants are probably impossible, because deviants probably require some local, biological process to produce this configuration. Such a process would, by definition, make the deviant a non-deviant. So, if such a process is necessary, then deviants are necessarily impossible. On the other hand, if we claim that only some of the possible biological processes that create phenomenal knowledge count as "earning experiences," then we need some basis for making this distinction. Considering the obstacles in the way of correlating biological processes with primitive experiential states, it is possible that no empirical evidence can ever justify making such a distinction. Therefore, we cannot assume that such a distinction is coherent, let alone plausible. The burden is on the supporters of deviants to argue for a distinction here, and such a case must rely on empirical evidence--we need a reason to discount some biological processes, and not others. Thus, without further argument and evidence, we may suppose that deviants are plausibly impossible, and that the very notion of a deviant is possibly incoherent.
Having supported the main thesis under consideration, I will conclude by trying to motivate a narrower thesis: The mere having of the right functional brain states may entail the having of the right experiences. I begin with an appeal to Paul Churchland (1989), who presents some thoughts on what phenomenal knowledge entails. According to him, phenomenal knowledge is not discursive knowledge. It is manifest in abilities to access representational states, where representational states are "learned configurations of synapses" which apparently ground "the many abilities we expect from color-competent creatures: discrimination, recognition, imagination, and so on" (Churchland, 1989, 70). In sum, a person who knows what it is like to see colors is a person who has a neurological configuration which represents a full spectrum of primitive color-perceptual elements. In this light, the possibility of deviants depends on the answer to this question: Is it possible for such a configuration to function without instantiating experiences which earn the right phenomenal knowledge?
I submit that the answer is possibly, if not plausibly, no. Critics will point to the commonsense belief that we do not constantly have, for example, visual experiences of red, and that we do not thereby suffer spells of not knowing what it is like to see red. But is this so obvious? How do we know that we are not always activating our most basic color-perceptual configurations? Reportability is not the key here. The most basic elements of phenomenal experience are not necessarily reportable as such. We can distinguish between a reportable experience and experience simpliciter. The fact that we cannot always distinguish a "red" experience (or an experience which earns phenomenal knowledge of redness) does not mean that we are not always having one. So how do we know that we are not always experiencing some phenomenal qualities which earn our phenomenal knowledge of red? Even when we close our eyes, we see colors--even when we are seeing black, we are seeing colors.
While "black" is sometimes defined as "the absence of light," this is not an accurate description of the black we experience. It is more accurate to say that "darkness" is the absence of light, where even in darkness we see black. In terms of pigmentation, black is a color, and it can be created by combining more basic elements in the color spectrum. Seeing black is not the same as not seeing anything at all. There is an experiential difference between seeing a black object and having a blindspot. So, arguably, when we see black, we see colors--and, arguably, we see all of the most primitive elements in our color-perceptual toolkit. It is therefore plausible that any person with a functional representation of the elements of color vision will experience all of those elements, and will thereby earn their phenomenal knowledge.
Phenomenal knowledge is earned if the experience requirement is satisfied. For example, since I have seen ripe tomatoes, my knowledge of what it’s like to see red is earned . . . To access phenomenal knowledge is to exercise closely related abilities, such as the ability to imagine, recognize, or remember relevant experiences. I access my phenomenal knowledge when I visualize a ripe tomato, stop at a traffic light, or have an episodic memory of seeing oxygenated blood. Phenomenal knowledge that is unearned, inaccessible, or both is deviant.
In what follows, I use "deviant" to refer to anybody who has deviant phenomenal knowledge. If deviants are possible, then it is possible for a person to know what it is like to see the color red without ever having seen, imagined, or hallucinated the color red. Discussions of deviants have focused on whether or not they create a problem for the knowledge argument against physicalism (Alter, 2008; Dennett, 2007; Mandik, 2010). However, I do not wish to discuss the knowledge argument here, nor do I want to discuss whether or not deviants cause a problem for anti-physicalists. Rather, I want to argue that the notion of a deviant is not obviously coherent, and that deviants are plausibly impossible. If the notion of a deviant is coherent, then the possibility of deviants remains an empirical question. Furthermore, I argue that the burden is on the supporters of deviants to substantiate their claim that deviants are both conceivable and possible.
Under some definitions of "phenomenal knowledge," the possibility of a deviant may be rejected a priori. According to the ability hypothesis, for example, phenomenal knowledge is defined as the abilities to recognize, imagine, and remember an experience (Churchland, 1989; Lewis, 1988; Nemirow, 1990, 2006). Yet, deviants cannot have true memories of the experiences they are supposed to have knowledge of. A deviant may think they are accessing memories of past experiences, but they are wrong. They are merely imagining experiences and wrongly judging them to be memories. Thus, the deviant does not have all of the right abilities, and so does not have the requisite phenomenal knowledge. In short, the deviant is not a deviant at all. According to the ability hypothesis, then, the notion of deviant phenomenal knowledge is self-contradictory.
Of course, the ability hypothesis is not universally lauded. Those who reject the ability hypothesis might suppose that phenomenal knowledge does not require the possession of true memories. Some might suppose that no memories are required at all, while others might claim that a deviant could have implanted memories which, though false in the strict sense, might still satisfy the requirement of phenomenal knowledge. Though I do not find either of these alternatives compelling (I am a supporter of the ability hypothesis), I will--for the sake of argument--accept that true memories are not required for phenomenal knowledge, and on that basis consider whether or not deviants are possible.
One way of approaching this topic is to consider Swampkinds. Davidson (1987) introduces the idea:
Suppose lightning strikes a dead tree in a swamp; I am standing nearby. My body is reduced to its elements, while entirely by coincidence (and out of different molecules) the tree is turned into my physical replica. My replica, The Swampman.....moves into my house and seems to write articles on radical interpretation. No one can tell the difference.
Enter Swamp Mary, a Swamp-version of Mary the super-scientist. Mary, as you may recall, learns all about color vision while confined to a black-and-white existence. Then she steps out of her room and sees a red tomato for the first time. Now she knows what it is like to see red. She earned it. A moment later, lightning strikes and Swamp Mary is born. Swamp Mary has access to the same knowledge Mary had, and so she should know what it is like to see a red tomato. Yet, Swamp Mary hasn't earned that knowledge. Her history does not include an experience of phenomenal redness. Swamp Mary is thus said to be a deviant (Alter, 2008; Dennett, 2007; Mandik, 2010).
(In Dennett's version, Swamp Mary is born before Mary ever sees a red tomato: the lightning strikes Mary and reconfigures her brain so that she is in the exact state she would have been in had she experienced the sight of a red tomato. The result is the same: lightning produces a Swamp version of Mary who supposedly knows what it is like to see red without ever having seen red.)
Whether Swamp Mary is possible depends partly on what it would take to create her. Millikan (1996) observes that there are limitations on the ways a Swamp person can come into existence. Biological science tells us:
You can't in principle build large organic molecules such as hemoglobin, they say, just by throwing the right amino acid molecules together at the right angles with the right energies and having them stick. . . Molecules like that must be built up through long chains of enzymatic cascading reactions that proceed in just the right order and require support from just the right helping catalysts timed to come on stage at just the right moments.
Thus, one way for a Swamp person to come about is through a long and complex biological process. However, this is not how Swampkinds are usually imagined. They are supposed to be born out of a sudden jolt of creative energy. (Lightning is often involved, perhaps for dramatic flair.) Is there another, more spontaneous way for Swamp people to come into being?
Millikan says yes, there is a way. First, she reminds us that the laws of physics are time-symmetric. What can happen going forward in time can also happen in reverse. So, if a person can be disintegrated into tiny particles--blown to bits, as it were--then a Swamp person can be reintegrated in exactly the same manner. Yet, as Millikan notes, such a Swamp person would live backwards in time:
A Swampman so originated will himself be running backwards when he has been formed. His cells will be getting younger rather than older, coalescing rather than dividing, returning nutrients to his blood which will run backwards, returning the nutrients to his digestive system from whence they will eventually emerge as new good hamburgers getting fresher by the moment.
I'm skipping over some of the details of Millikan's analysis, but the point is clear enough. If Swamp Mary is going to happen in this world (or a world reasonably similar to this one), then it can only happen in conformity with the laws of physics, and this places constraints on how she can be created. It is most likely that Swamp Mary can only come about via a long and complex biological process, the full details of which are as yet unknown.
Supposing that Swamp Mary is possible, there is also the question of whether or not she really is a deviant. We cannot assume she is. For example, Millikan (1996) argues that we cannot attribute beliefs or other intentional states to Swampkinds, and this would preclude any knowledge attributions. She quotes a point made in her (1984):
Suppose that by some cosmic accident a collection of molecules formerly in random motion were to coalesce to form your exact physical double. ...that being would have no ideas, no beliefs, no intentions, no aspirations, no fears, and no hopes....This because the evolutionary history of the being would be wrong.
Davidson (1987) makes a similar point, though instead of appealing to the lack of evolutionary history, he appeals to the lack of individual history, writing: "I don't see how my replica can be said to mean anything by the sounds it makes, nor to have any thoughts."
The Davidson-Millikan objection is that, because Swampkinds lack the right histories (be they individual, evolutionary, or both), we cannot treat them like human beings. They cannot be deviants. I do not know how much weight is given to this argument in the literature, but it does appear to be a coherent objection. This makes the appeal to Swampkinds somewhat more difficult. [Update: see here for more on this line of thought].
In any case, all of the deviant eggs are not in the Swamp basket. Alter (2008) mentions other seemingly plausible ways of creating a deviant:
Unger imagines that scientists construct a man who is “cell‐part for cell‐part, cell for cell, nervous structure for nervous structure identical to” a man who both knows what it’s like to see red and has come upon this knowledge the ordinary way (Unger 1966: 50). Others (e.g., Lewis 1988, Alter 1998, Stoljar 2005) imagine cases in which surgeons operate on a person who has never seen red, creating brain structures similar to those found in the brains of people who have seen red.
In all of these cases, including Swamp Mary, the alleged deviant requires some long, elaborate, and neurologically complex process in order to produce their phenomenal knowledge. Yet, such processes cannot entail an experience of phenomenal redness--or any other experience which could earn phenomenal knowledge of redness, such as experiences which are simpler than experiences of phenomenal redness and out of which experiences of phenomenal redness might be composed.
(There may be disagreement about whether an experience of phenomenal redness is simple or complex. I will not argue one way or the other here. However, I think all sides agree that some experiences are composed of smaller or more primitive experiential components. Presumably, if one earns phenomenal knowledge of the more primitive components, one has earned phenomenal knowledge of the composites.)
Alter, Dennett, and Mandik are willing to assume that deviants could be constructed and function without ever experiencing even a hallucination of the color red. I find that remarkable, since there is no consensus about what sorts of physiological processes are necessary or sufficient for phenomenal consciousness. Any consensus can only be reached by appeal to the empirical sciences, and this makes the possibility of deviants an empirical question. I am inclined to think that deviants are impossible, though I admit that evidence could prove me wrong.
My thesis is thus: A person cannot be put into a functional state of knowing what it is like to see red without being put in experiential states which earn that knowledge. My intuition is that the elaborate process of constructing the right neurological configurations, or the very having of those configurations in a functionally operative state, necessarily entails perceptual experiences which are sufficient to earn all of their phenomenal knowledge. Of course, not being able to explain how such configurations can be constructed, I do not expect my intuition to be compelling to anybody. However, compelling or not, I do think this view is plausible. Furthermore, I think the burden of proof is on the people who disagree with me.
Here is my argument. We might define an "earning experience" as any local, biological process capable of producing the right synaptic configuration. In such a case, deviants are probably impossible, because deviants probably require some local, biological process to produce this configuration. Such a process would, by definition, make the deviant a non-deviant. So, if such a process is necessary, then deviants are necessarily impossible. On the other hand, if we claim that only some of the possible biological processes that create phenomenal knowledge count as "earning experiences," then we need some basis for making this distinction. Considering the obstacles in the way of correlating biological processes with primitive experiential states, it is possible that no empirical evidence can ever justify making such a distinction. Therefore, we cannot assume that such a distinction is coherent, let alone plausible. The burden is on the supporters of deviants to argue for a distinction here, and such a case must rely on empirical evidence--we need a reason to discount some biological processes, and not others. Thus, without further argument and evidence, we may suppose that deviants are plausibly impossible, and that the very notion of a deviant is possibly incoherent.
Having supported the main thesis under consideration, I will conclude by trying to motivate a narrower thesis: The mere having of the right functional brain states may entail the having of the right experiences. I begin with an appeal to Paul Churchland (1989), who presents some thoughts on what phenomenal knowledge entails. According to him, phenomenal knowledge is not discursive knowledge. It is manifest in abilities to access representational states, where representational states are "learned configurations of synapses" which apparently ground "the many abilities we expect from color-competent creatures: discrimination, recognition, imagination, and so on" (Churchland, 1989, 70). In sum, a person who knows what it is like to see colors is a person who has a neurological configuration which represents a full spectrum of primitive color-perceptual elements. In this light, the possibility of deviants depends on the answer to this question: Is it possible for such a configuration to function without instantiating experiences which earn the right phenomenal knowledge?
I submit that the answer is possibly, if not plausibly, no. Critics will point to the commonsense belief that we do not constantly have, for example, visual experiences of red, and that we do not thereby suffer spells of not knowing what it is like to see red. But is this so obvious? How do we know that we are not always activating our most basic color-perceptual configurations? Reportability is not the key here. The most basic elements of phenomenal experience are not necessarily reportable as such. We can distinguish between a reportable experience and experience simpliciter. The fact that we cannot always distinguish a "red" experience (or an experience which earns phenomenal knowledge of redness) does not mean that we are not always having one. So how do we know that we are not always experiencing some phenomenal qualities which earn our phenomenal knowledge of red? Even when we close our eyes, we see colors--even when we are seeing black, we are seeing colors.
While "black" is sometimes defined as "the absence of light," this is not an accurate description of the black we experience. It is more accurate to say that "darkness" is the absence of light, where even in darkness we see black. In terms of pigmentation, black is a color, and it can be created by combining more basic elements in the color spectrum. Seeing black is not the same as not seeing anything at all. There is an experiential difference between seeing a black object and having a blindspot. So, arguably, when we see black, we see colors--and, arguably, we see all of the most primitive elements in our color-perceptual toolkit. It is therefore plausible that any person with a functional representation of the elements of color vision will experience all of those elements, and will thereby earn their phenomenal knowledge.
[Updated on May 5, 2010]
References
- Torin Alter (1998). "A Limited Defense of the Knowledge Argument." Philosophical Studies. 90 (1):35-56.
- Torin Alter (2008). "Phenomenal Knowledge Without Experience." In Edmond Wright (ed.), The case for qualia.
- Paul M. Churchland (1989). A Neurocomputational Perspective: The Nature of Mind and the Structure of Science. MIT Press.
- Donald Davidson (1987). "Knowing One's Own Mind." Proceedings and Addresses of the American Philosophical Association 60 (3):441-458.
- Daniel C. Dennett (2006). "What Robomary Knows." In Torin Alter & Sven Walter (eds.), Phenomenal Concepts and Phenomenal Knowledge: New Essays on Consciousness and Physicalism. Oxford University Press.
- David Lewis (1988). "What Experience Teaches." In Proceedings of the Russellian Society. Sydney: University of Sydney. Rpt. in Mind and Cognition: a Reader, W. Lycan, (ed.). Cambridge: Basil Blackwell, 1990, pp. 499‐518.
- Pete Mandik (2010). "Swamp Mary's Revenge: Deviant Phenomenal Knowledge and Physicalism." Philosophical Studies 148 (2).
- Millikan, R. (1984). Language, Thought and Other Biological Categories. Cambridge MA: MIT Press.
- Ruth G. Millikan (1996). "On Swampkinds." Mind and Language 11 (1):103-17.
- Laurence Nemirow (1990). "Physicalism and the Cognitive Role of Acquaintance." In William G. Lycan (ed.), Mind and Cognition. Blackwell.
- Laurence Nemirow (2006). "So This is What It's Like: A Defense of the Ability Hypothesis." In Torin Alter & Sven Walter (eds.), Phenomenal Concepts and Phenomenal Knowledge: New Essays on Consciousness and Physicalism. Oxford University Press.
- Daniel Stoljar (2005). "Physicalism and Phenomenal Concepts." Mind and Language 20 (2):296-302.
- Peter K. Unger (1966). "On Experience and the Development of the Understanding." American Philosophical Quarterly 3 (January):48-56.
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