The notion of particular pain x belonging to a single person, and to no one else, has been said to lead to the position of the necessary irreducibility of pain. (This position has been applied to all other phenomenal states too.) It’s also said that a particular pain is “not dependent for its existence on anyone else”.
So where do we go from there?
If we communicate our pain to others, then we’ll use a public language to do so. (Wittgenstein, of course, stressed the point that all languages must be public.) And even that private experience will be coloured by a public language — at least to some extent. So it can be accepted that there is a sensory or experiential aspect — or even basis — to the pain. However, that can’t be communicated in its (as it were) purity to another person or even to oneself! And it certainly isn’t what’s often called an “objective fact”.
So what is it?
Another argument for the particularity — and therefore (perhaps) non-scientific nature — of pain is summed up in this sentence:
“No one else could have that particular pain.”
Is that any more strange than the fact that this brick can’t be like that brick over there? In addition, the precise colour (or trope) of that bee over there is unique. And even public utterances about any given pain x are singular in the sense that each one will be unique in some way. So are pains are anymore particular than these other things?
It’s also argued that no one else can feel my particular pain in the way I feel it. Ditto. One brick may be very similar to another brick. Still, it’s not the same brick.
Pain as an Objective Fact
Some philosophers have argued that a person’s pain is an “objective fact”: as as objective as anything else.
Sure; a pain is real and part of reality; though is it also an objective fact or an objective… anything?
There is indeed “something it is like” to be stung by a bee. However, calling that something an “objective fact” doesn’t seem to be correct.
Of course none of the above is a complete denial of the private aspects of a particular pain. Yet since we take a very circuitous route to the physical reality of, say, DNA, atoms or electrons, perhaps we can do the same for pains. (It’s true that this isn’t an exact like-for-like comparison.) Nonetheless, being “externally identifiable” may still not be a necessary criterion for something’s being physical.
Just as we can’t perceive particles, so we can’t feel (or perceive) another person’s pain — except through that person’s verbal and bodily behaviour. We believe in the existence of, say, quarks because of a lot of theory, models and, yes, observable phenomena. Then again, the clues we have for another person’s pain don’t necessarily mean that the pain is physical. The clues (behaviour) are physical; though their causes may be non-physical. (Human behaviour being equivalent to the “traces” of particles in, say, a cloud chamber.)
Consequently, much of behaviourism was about ways to make pain — and the mental generally — externally identifiable and thus scientifically kosher. Yet it can still be said that pain — and other private mental phenomena - underpin (whatever that may mean) behaviour and language use; as well as mental functions as they’re expressed in (to use Quine’s term) “overt behaviour”.
So, when it came to behaviourism at least, all this meant that various philosophical problems still remained when it came to the privacy of pain and indeed all other mental states.