The only 'comunication' in which there is perfect understanding, with no possbility of misunderstanding, is the communion of empathy. Only when both mutually experience the 'feeling' as one can we truly 'know' "what it's like".
Through language, prose, poetry, art, etc... we also attempt to demonstrate 'what it's like'. There is a 'range' of success.

To understand "Ian feels sad" we only have to know that Ian is sad and what it means for someone to be sad. This is not to say, for example, that Travis's sadness is the same as Ian's, and it is not to say that we can only know either's sadness if we can know that particular internal and external events that supposedly led up to to their unfortunate state (these are more of an secondary explanation).

There are somethings that could not be explained by reduction to something else. Here is what i mean. Think of a particular "feeling" you had toward a person, or a book. The sense of honor, and dignity you felt when you did something good. You can always explain it using biological terms from a third person perspective of what is going on in your body. You could write a paper that describes the precise biological sequence of events that lead the particular feeling you felt. Someone can read the paper, and understand the sequence of events that lead to your particular feeling. Does he really understand how your feel? I don ` t think so. Here is why. Suppose you talk to your friend, and he had a bad day. You want to comfort him, and you tell him that you understand what he is going through. You don` t mean you understand the sequence of biological, chemical events that goes out in his body that lead to him feeling sad. What you mean is that you understand what it is like to have a bad day. Subjective experience deals with the question of "what is it like".

Other examples:

Ask a blind person what the color blue. He might define blue as a particular frequency of a EM wave. I doubt our intention is to know the frequency of EM wave. What we mean is how it feels to see the color blue. How it feels when the light hits our eyes, and the sensation it invokes.

And, even if you know what it is like to have a bad day, you do not know what it is like for your friend to have a bad day, you know only what it is like for you to have a bad day. So you cannot reduce what it is like for someone else to experience something to what it is like for you to experience that thing. (See, "What is it like to be a bat" by, Thomas Nagel. I think it is on the Web").

Think about the reply one more time. When mary had a bad day, and john comfort her by saying " i know what you mean". Does he mean he knows "exactly" the situation mary is in, and her mental state? Obviously not. Like the telmud said, you cannot be in another people` s shoe unless you are the people. John would be a crappy stocker to know exactly the detail of mary ` s day. What he means is that he understand Mary ignore "mental state". Thus, John knows and only need to know "what it is like" of the emotional state of mary, but not every detail of mary ` s experience.

Nothing you say above is inconsistent with what I said, so far as I can see. I simply pointed out that knowing what it is like for you to have a bad day is not the same as what it is like for Mary to have a bad day. Do you not agree with that? I know what John means. But how is what John means an objection to what I just said?

My example works only to the extend that john does need to know "how it feels" to be in mary ` s shoe. You come alone and say john does not know the detail of mary ` s day. Well, what am i suppose to think? Your comment ( if you knowing it our not) try to avoid the question of "how it feels" for john. You are like saying, when john say he knows mary` s mental state, but he does not know exactly mary` s experience. The latter is unimportant to the question at hand, and i don` t even want the suggestion it does matter.

But it really has nothing to do with what you call the "details" of Mary's experience.

It has to do with the fact that according to you, when John says he knows how Mary feels, he is really saying that he knows how he would feel if he were in the same situation Mary finds herself in.

But, not that he know how Mary herself feels.

And that is very different. For those are not even about the same thing. The first is about John. The second is about Mary.

what exactly did i say?



true






Why not? If i say i am happy right now. Do you have any problem with understanding how i feel?( Obviously not, because i told you, and you understand what it is like to feel happy)




OK. Give me an argument.

I know what it is like for me to feel happy. I don't know what it is like for you to feel happy.

The missing premise is that if they about two different people, then they are different.

Can you be more clear about this premise? Two people might have two different rooms, but there is nothing logically impossible that they share the same room( this room encompass the previous two rooms). Similarly, two objects can have two different mirror images, but nothing prevent them from having one mirror image( Imagine 2 objects, and three mirrors).
Two red objects might have their own set, but nothing prevent them from being members of the same set( the union of the previous two set).

Of course. If I make a statement about A, that statement is a different statement from a statement about B. Of course, that does not prevent them from both being statements about persons. But it does prevent them from being statements about the same person.