The knowledge argument aims to establish that conscious experience involves non-physical properties. It rests on the idea that someone who has complete physical knowledge about another conscious being might yet lack knowledge about how it feels to have the experiences of that being. It is one of the most discussed arguments against physicalism. The Knowledge Argument became the subject of intense philosophical discussion following its canonical formulation by Frank Jackson However, there are numerous precursors of this argument in the literature.
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The knowledge argument aims to establish that conscious experience involves non-physical properties. It rests on the idea that someone who has complete physical knowledge about another conscious being might yet lack knowledge about how it feels to have the experiences of that being.
It is one of the most discussed arguments against physicalism. The Knowledge Argument became the subject of intense philosophical discussion following its canonical formulation by Frank Jackson However, there are numerous precursors of this argument in the literature. These thought-experiments typically involve a being who has complete knowledge of the physical information or physical facts concerning certain experiences, but who it is claimed lacks knowledge of what those experiences are like.
Dunne Around the same time as Dunne was writing, C. Broad used a thought-experiment as part of an argument against a mechanistic version of physicalism. Feigl briefly discusses the epistemic limitations of a Martian who studies human behavior but does not share human sentiments:. Farrell had earlier presented a similar thought experiment featuring a Martian; in this version, it is humans who lack knowledge of what it is like for the Martian to exercise his sensory capacities , ; though Farrell ultimately argues that this thought experiment does not present a challenge to physicalism.
Paul E. More recent examples from the literature come closer to being versions of the Knowledge Argument rather than merely precursors to it. For example, consider the following statement of the knowledge intuition by Nicholas Maxwell:. Finally, it is worth mentioning the extremely influential thought experiment described by Thomas Nagel Nagel does not argue against physicalism, but rather claims that we presently have no understanding of how it can be true.
In Section 4. Frank Jackson formulates the intuition underlying his Knowledge Argument in a much cited passage using his famous example of the neurophysiologist Mary:. Most authors who discuss the knowledge argument cite the case of Mary, but Frank Jackson used a further example in his seminal article: the case of a person, Fred, who sees a color unknown to normal human perceivers.
We might want to know what color Fred experiences when looking at things that appear to him in that particular way.
It seems clear that no amount of knowledge about what happens in his brain and about how color information is processed in his visual system will help us to find an answer to that question. In both cases cited by Jackson, an epistemic subject A appears to have no access to particular items of knowledge about a subject B : A cannot know that B has an experience of a particular quality Q on certain occasions.
This particular item of knowledge about B is inaccessible to A because A never had experiences of Q herself. The argument may thus be reformulated in two different ways:. The conclusion of the stronger version of the argument 3b is an ontological claim that the physicalist must reject.
The conclusion of the weaker version of the argument is merely an epistemological claim that is compatible with denying the existence of non-physical facts. As many have pointed out, the result of the weaker version 3a does not imply the result of the stronger version 3b. That a person has incomplete knowledge about a certain topic does not imply without further assumptions that there is some specific fact she does not have knowledge of.
The example of knowledge about oneself de se knowledge may illustrate the general point. He lacks a specific locating piece of de se knowledge. Still, there need not be any fact concerning the location of people that John does not have knowledge of.
It does not follow from the description of the case that John does not have knowledge of the fact that John is in Amsterdam. John may well know that John is in Amsterdam but, having forgotten that he is himself John, he may fail to conclude that he is now in Amsterdam. If John finally learns that he is in Amsterdam, he does not thereby learn a new fact — or so many philosophers would insist — he gains new knowledge of a fact that he already knew in a different way.
Many authors accept the weaker version of the argument but reject the stronger one for the reason just sketched: they admit that Mary gains new propositional knowledge but deny that she thereby comes to know facts that she did not know before in some other way.
These authors accept the first premise of both versions of the argument and the second premise of the first version as well, but they deny the second premise of the second version and insist that 2a does not imply 2b. Others deny even the weaker version V1 and claim that Mary does not gain any new propositional knowledge no new knowledge about something that is the case, no factual knowledge.
To locate the different points of disagreement it is helpful to formulate the stronger version of the argument more explicitly. Once C1 and C2 are accepted, there is obviously no way to avoid C3 which follows logically from the former two. Moreover, is seems hard to deny that it is in principle possible to have complete physical knowledge about human color vision or about an appropriately chosen part thereof. If so, premise P1 should be accepted as an appropriate description of a legitimate thought experiment.
To avoid the antimaterialist conclusion C3 the physicalist can a object against the inference from P1 to C1 a minority of philosophers have chosen this strategy, see Section 4. The knowledge argument is often cited as one of those anti-physicalist qualia-based arguments that are supposed to justify property dualism.
The above formulation, however, does not explicitly mention non-physical properties but only non-physical facts. But the relation between the two claims is obvious.
Friends of the knowledge argument will say that the facts at issue are non-physical because they involve the exemplification of non-physical properties e. It would be natural to define physical facts as those facts that can be expressed in this way. Contrary to Mary at a later moment t 2 she gets acquainted with colors by seeing arbitrarily colored objects abstract paintings, red chairs, blue tables, etc. Marianna is therefore unable to relate the kinds of color experiences she now is acquainted with to what she already knew about them at t 1.
At t 2 , Marianna may wonder which of four slides a red, a blue, a green and a yellow slide appears to her in the color normal people experience when looking at the cloudless sky.
At t 2 Marianna knows, in a sense, what it is like to have experiences of red, blue, etc. But she still lacks the relevant items of knowledge about what other people experience: there is a clear sense in which she still may not know that the sky appears blue to normal perceivers, she may even have the false believe that it appears to normal perceivers like the red slide appears to her and thus believe, in a sense, that the sky appears red to normal perceivers.
Only at t 3 , when Marianna is finally released and sees the sky, does she gain this item of knowledge. By acquiring these concepts she acquires the capacity to ask new questions, and to form new eventually false hypotheses e.
Only at t 3 does she acquire the kind of knowledge that the knowledge argument is concerned with knowledge that involves the application of phenomenal concepts about experiences of other people.
Rather, or so one may argue, Mary and Marianna acquire a particular kind of belief that the sky appears blue to normal perceivers, namely the phenomenal belief that it appears blue to normal perceivers, where phenomenal belief involves the application of the appropriate phenomenal concept. Both may have believed, in a sense the non-phenomenal sense that does not require use of phenomenal concepts that the sky appears blue to normal perceivers while still in their black-and-white environment they may have been told so by their friends.
For the distinction between phenomenal and non-phenomenal belief see Nida-Rumelin and Some authors have raised doubts about the thought experiment itself. It is sometimes pointed out, for example, that merely confining Mary to a monochromatic environment would not prevent her from having color experiences see Thompson , or that, after release, she would not be able to see colors.
But the example can be refined to meet these objections. Mary might be monochromatic from birth and changed into a normal perceiver by some medical procedure. It is sometimes objected that already accepted or future results of visual science are or might be incompatible with the existence of a Mary-case a person with monochromatic experience who becomes a normal color perceiver later or that such results might require to preserve consistence with visual science the introduction of so many additional assumptions that the conceivability of the example becomes doubtful.
To this one might reply that the thought experiment need not be compatible with visual science. If the case of a person with monochromatic vision who turns into a normal perceiver really does involve serious difficulties for materialism, then the mere fact if it were one that our visual apparatus excludes the actual existence of such a case does not seem to provide a convincing reply for the materialist.
But this point the relevance or irrelevance of visual science in this context has not received much discussion in the literature. It has, however, been pointed out see Graham and Horgan, , footnote 4 with its reference to Shepard that at least presently available results of color vision science do not exclude a Mary-case. The psychologist Knut Nordby was a real life case of a color vision specialist who was also a complete achromat. Another doubt about the thought experiment is raised by the claim that a person who is confined to a monochromatic environment but knows everything physical there is to know about visual color experience would be able to figure out what colored things look like and thus would e.
Dennett ; Dennett ; Churchland ; Maloney , Probably the most common reaction to this is simply to doubt the claim. But it is not clear that the claim, if correct, would undermine the knowledge argument. The opponent would have to show that complete physical knowledge necessarily involves the capacity to imagine blue. Arguably a subject whose visual apparatus is not suited for visual experiences at all will not be able to develop the capacity to imagine colors on the basis of physical knowledge alone, even if this were true for Mary.
Some have argued that Mary would recognize the colors when first seeing them on the basis of her complete physical knowledge about color vision see Hardin A possible and common response is to simply doubt these claims.
But, in any case, it is not clear that these claims undermine the knowledge argument. One may respond along the following lines: If Mary when first confronted with red were able to conclude that she is now seeing what people call red, she thereby acquires a large set of new beliefs about red experiences that they are produced by roses, such-and-such wavelength combinations and so on.
On the basis of seeing red she a acquires a new phenomenal concept of red and b she forms new beliefs involving that new concept using her previously acquired physical knowledge. It may appear obvious that premise P1 Mary has complete physical knowledge about human color vision implies C1 Mary knows all the physical facts about human color vision. If all physical facts can be known under some physical conceptualization, then a person who has complete physical knowledge about a topic knows all the relevant physical facts.
But a few philosophers can be understood as objecting against precisely this apparently unproblematic step. Harman argues that Mary does not know all the functional facts concerning human color vision because she lacks the concept of what it is for an object to be red, blue, etc.
Flanagan distinguishes metaphysical physicalism from linguistic physicalism. Alter points out that the knowledge argument needs the premise that all physical facts can be learned discursively and argues that this assumption has not been established. It may be argued against this view that it becomes hard to understand what it is for a property or a fact to be physical once we drop the assumption that physical properties and physical facts are just those properties and facts that can be expressed in physical terminology.
Two different versions of the No Propositional Knowledge -View have been proposed. According to the Ability Hypothesis most prominently defended in Lewis , and in Nemirow , , , Mary does not acquire any new propositional knowledge after release no knowledge about something that is the case, no factual knowledge , but only a bundle of abilities like the ability to imagine, remember and recognize colors or color experiences.
According to Lewis,. Bence Nanay suggests that what Mary acquires is the ability to discriminate between different types of awareness, i. According to the HPI knowing what it is like is propositional in the following sense: coming to know what it is like involves the elimination of hitherto open possibilities.
Therefore: The Ability Hypothesis should be preferred. Note that the Ability Hypothesis is compatible with the view that we do sometimes acquire propositional knowledge on the basis of getting acquainted with a new kind of experience from the first person perspective.
The following remarks by Levin are hard to deny:. But, as pointed out by Tye , this does not undermine the Ability Hypothesis. The Ability Hypothesis implies that there is some knowledge that can only be acquired by having experiences of a particular kind and that this knowledge is nothing but knowing-how. This of course does not exclude that there also is propositional knowledge that can be acquired by getting acquainted with kinds of experiences from the first person perspective.
The proponent of the Ability Hypothesis only has to insist that, if there is such propositional knowledge, then it need not be acquired on that particular basis but is accessible in other ways as well. It has been argued against Nemirow that the ability to imagine having an experience of a particular kind is neither necessary nor sufficient for knowing what it is like to have that kind of experience.
Epiphenomenalism is the view that mental events are caused by physical events in the brain, but have no effects upon any physical events. Behavior is caused by muscles that contract upon receiving neural impulses, and neural impulses are generated by input from other neurons or from sense organs. On the epiphenomenalist view, mental events play no causal role in this process. Huxley , who held the view, compared mental events to a steam whistle that contributes nothing to the work of a locomotive. The modern discussion of epiphenomenalism, however, traces back to a 19th century context, in which a dualistic view of mental events was assumed to be correct.
Qualia: The Knowledge Argument
Jackson quotes are from "Epiphenomenal Qualia. Jackson describes himself as "a qualia freak". The word "qualia" is the plural of the word "quale" pronounced KWA-lay. A quale is a "raw feel". Examples of qualia include "the hurtfulness of pains, the itchiness of itches, pangs of jealousy" and the taste of pineapple, the smell of a rose, etc. Some people think qualia are the obvious counterexample to physicalism's claim that everything about the mental can be understood in purely physical terms.
Jackson offers the following argument against physicalism:. Although he finds this a perfectly good argument, he realizes that it will not persuade everyone. The Knowledge Argument for Qualia. People vary in their ability to discriminate colors. Jackson has us imagine this person Fred who is able to discriminate two different colors of perfectly ripe tomatoes, which he calls red 1 and red 2. Fred consistently sorts the tomatoes the same way.