In its most general form, functionalism defines mental states and processes by their causal or functional relations to each other and to perceptual inputs from the world outside and behavioral outputs expressed in action.(p. 32)

First, when you attend to a pain in your leg or to your experience of the redness of an apple, you are aware of an intrinsic quality of your experience, where an intrinsic quality is a quality something has in itself, apart from its relations to other things. This quality of experience cannot be captured in a functional definition, since such a definition is concerned entirely with relations, relations between mental states and perceptual input, relations among mental states, and relations between mental states and behavioral output. For example, "An essential feature of [Armstrong's functionalist] analysis is that it tells us nothing about the intrinsic nature of mental states... He never takes seriously the natural objection that we must know the intrinsic nature of our own mental states since we experience them directly

Second, a person blind from birth could know all about the physical and functional facts of color perception without knowing what it is like to see something red. So, what it is like to see something red cannot be explicated in purely functional terms

Third, it is conceivable that two people should have similarly functioning visual systems despite the fact that things that look red to one person look green to the other, things that look orange to the first person look blue to the second, and so forth (Lycan 1973, Shoemaker 1982). This sort of spectrum inversion in the way things look is possible but cannot be given a purely functional description, since by hypothesis there are no functional differences between the people in question. Since the way things look to a person is an aspect of that person's mental life, this means that an important aspect of a person's mental life cannot be explicated in purely functional terms.

There are many other examples of intentionality. Ponce de Leon searched Florida for the Fountain of Youth. What he was looking for was a fountain whose waters would give eternal youth to whoever would drink them. In fact, there is no such thing as a Fountain of Youth, but that does not mean Ponce de Leon wasn't looking for anything. He was looking for something. We can therefore say that his search had an intentional object. But the thing that he was looking for, the intentional object of his search, did not (and does not) exist.

"Ponce de Leon was searching for the Fountain of Youth. But there is no such thing. So he must have been searching for something mental." This is just a mistake. From the fact that there is no Fountain of Youth, it does not follow that Ponce de Leon was searching for something mental. In particular, he was not looking for an idea of the Fountain of Youth. He already had the idea. What he wanted was a real Fountain of Youth, not just the idea of such a thing

In the same way, what Eloise sees before her is a tree, whether or not it is a hallucination. That is to say, the content of her visual experience is that she is presented with a tree, not with an idea of a tree. Perhaps, Eloise's visual experience involves some sort of mental picture of the environment. It does not follow that she is aware of a mental picture. If there is a mental picture, it may be that wha she is aware of is whatever is represented by that mental picture; but then that mental picture represents something in the world, not something in the mind.

But this ambiguity in perceptual verbs does not affect the point I am trying to make. To see that it does not, let us use "see†" ("see-dagger") for the sense of "see" in which the object seen might not exist, as when Macbeth saw a dagger before him.' And let us use it see*" ("see-star") for the sense of "see" in which only things that exist can be seen. Macbeth sawt a dagger but he did not see* a dagger.

Eloise is aware of the tree as a tree that she is now seeing. So, we can suppose she is aware of some features of her current visual experience. In particular, she is aware that her visual experience has the feature of being an experience of seeing a tree. That is to be aware of an intentional feature of her experience; she is aware that her experience has a certain content.

In the case of a painting Eloise can be aware of those features of the painting that are responsible for its being a painting of a unicorn. That is, she can turn her attention to the pattern of the paint on the canvas by virtue of which the painting represents a unicorn. But in the case of her visual experience of a tree, I want to say that she is not aware of, as it were, the mental paint by virtue of which her experience is an experience of seeing a tree. She is aware only of the intentional or relational features of her experience, not of its intrinsic nonintentional features.

It is very important to distinguish what are experienced as intrinsic features of the intentional object of experience from intrinsic feat of the experience itself.

It is true that, if Melvin hallucinates a pink elephant, the elephant that Melvin sees does not exist. But the pain in your leg resulting from a slipped disc in your back certainly does exist.2 The pain is not an intentional object in quite the way the elephant is. The pain in your leg caused by the slipped disc in your back is more like the afterimage of a bright light. If you look at a blank wall, you see the image on the wall. The image is on the wall, the pain is in your leg. There is no physical spot on the wall, there is no physical disturbance in your leg. The afterimage exists, the pain exists. When we talk about afterimages or referred pains, some of what we say is about our experience and some of what we say is about the intentional object of that experience. When we say the pain or afterimage exists, we mean that the experience exists. When we say that the afterimage is on the wall or that the pain is in your leg, we are talking about the location of the intentional object of that experience.

the intentional content of an experience comprises everything one is aware of in having that experience.

First, when you attend to a pain in your leg or to your experience of the redness of an apple, you are aware of an intrinsic quality of your experience, where an intrinsic quality is a quality something has in itself, apart from its relations to other things. This quality of experience cannot be captured in a functional definition, since such a definition is concerned entirely with relations, relations between mental states and perceptual input, relations among mental states, and relations between mental states and behavioral output. For example, "An essential feature of [Armstrong's functionalist] analysis is that it tells us nothing about the intrinsic nature of mental states... He never takes seriously the natural objection that we must know the intrinsic nature of our own mental states since we experience them directly

When you attend to a pain in your leg or to your experience of the redness of an apple, you are attending to a quality of an occurrence in your leg or a quality of the apple. Perhaps this quality is presented to you as an intrinsic quality of the occurrence in your leg or as an intrinsic quality of the surface of the apple. But it is not at all presented as an intrinsic quality of your experience. And, since you are not aware of the intrinsic character of your experience, the fact that functionalism abstracts from the intrinsic character of experience does not show it leaves out anything you are aware of.

A person blind from birth could know all about the physical and functional facts of color perception without knowing what it is like to see something red. So, what it is like to see something red cannot be explicated in purely functional terms.

You can represent that to yourself only if you have the relevant concept of what it is for something to be red. The blind person lacks the full concept of redness that a sighted person has; so the blind person cannot fully represent what it is for a sighted person to see something red.

We are now in a position to assess the claim that the person blind from birth could know all the physical and functional facts about color perception without knowing what it is like to see something red. I claim that there is one important functional fact about color perception that the blind person cannot know, namely, that there is a concept R such that when a normal perceiver sees something red in good lighting conditions, the perceiver has visual experience with a representational structure containing this concept R

It is conceivable that two people should have similarly functioning visual systems despite the fact that things that look red to one person look green to the other, things that look orange to the first person look blue to the second, and so forth. This sort of spectrum inversion in the way things look is possible but cannot be given a purely functional description, since by hypothesis there are no functional differences between the people in question. Since the way things look to a person is an aspect of that person's mental life, this means that there is an important aspect of a person's mental life that cannot be explicated in purely functional terms.

Normally, a perceiver uses this representation as his or her representation of the environment. That is to say, the perceiver uses it in order to negotiate the furniture. In still other words, this representation is used as the perceiver's belief about the environment. This sort of use of perceptual representations is the normal case, although there are exceptions when a perceiver inhibits his or her natural tendency and refrains from using a perceptual representation (or certain aspects of that representation) as a guide to the environment, as a belief about the surroundings. The content of perceptual representation is functionally defined in part by the ways in which this representation normally arises in perception and in part by the ways in which the representation is normally used to guide actions

The hypothesis of the inverted spectrum objection is that the strawberry looks different in color to Alice and to Fred. Since everything is supposed to be functioning in them in the normal way, it follows that they must ha different beliefs about the color of the strawberry. If they had the same beliefs while having perceptual representations that differed in content, then at least one of them would have a perceptual representation that was not functioning as his or her belief about the color of the strawberry, which is to say that it would not be functioning in what we are assuming is the normal way.

If Alice and Fred meant the same thing by their color terms, then either (a) one of them would not be using these words to express his or her beliefs about color or (b) one of them would not be using his or her perceptual representations of color as his or her beliefs about color.

the intentional content of an experience comprises everything one is aware of in having that experience.