A Puzzle About Perception
Here is a strange fact about the universe: nothing that can be perceived from the inside can be perceived from the outside, and nothing that can be perceived from the outside can be perceived from the inside. You feel an intense pain—you plainly perceive the pain—but no one around you can sense your pain. They may know you have a pain but they don’t perceive it, whereas you perceive it only too well. They may look you over carefully, even touch and smell you, but your pain will never be an object of perception to them. Your pain is perceptually closed to them despite its openness to you. It is as if the pain can only be perceived from one position in the universe—the one that you alone occupy. You perceive it easily and automatically, but no one else can do this; their senses are not up to the task. Hence we have the common belief that the mind is an invisible thing (it’s not just pain that only the subject himself can perceive). Likewise, if a thing can be perceived in the normal third-person way, it is not perceived in the first-person way: if a tree is perceived by the senses, it is not perceived by itself in the introspective mode. Even if the object in question has introspective awareness, the perceived fact will not be introspected by the object: we don’t introspect our own brain states though they are perceptible to others (and ourselves, in principle). If a thing is perceived by the senses it is not perceived by introspection. One sort of perception precludes the other: if you can see it in one way you can’t see it the other way. Either the thing is perceived introspectively or it is perceived externally but never both. If it is suited to one kind of perception it is not suited to the other. This is odd, puzzling, because it is hard to see why things have to divide up this way. Why can’t pains be perceived both ways? Why can’t brain states be introspected as well as seen with the eyes? Why is perception limited in these ways? We can have beliefs and knowledge about things from both points of view, but not the means of cognition we are calling perception (apprehension, sensation, feeling, acquaintance). I know I have a pain and so do you, and I can in principle know my brain states as well as you; but perception does not line up with this. If something can be sensed in one way, it cannot be sensed in the other way. The universe seems to be imposing arbitrary rules on the scope of perception.
It might be wondered how deep these rules go. Is it just contingent that pain states can’t be perceived by all and sundry (“I see your pain and it looks like a nasty one”) and that physical properties are not perceived by introspection (“My occipital cortex feels like its firing nicely today”)? Are there possible worlds in which doctors can see what you are feeling pain-wise and ordinary people can introspectively report on their brain states? I don’t want to discuss the question of whether the current set-up is logically or metaphysically necessary (the question is by no means easy), but it seems clear that it is deep-seated so far as our actual universe is concerned. As things are, the rules of perception are rigid in this respect: there are never any exceptions, and it is hard to see how there could be. It isn’t as if you just have to put on some special goggles and other people’s pain will leap into view in vivid 3-D. Nor can concentrating your attention on your head area cause your brain to disclose itself to your introspective faculty. Perceptual closure of the type I am describing looks written deep into the structure of the universe as we have it. But it is metaphysically puzzling; there is a kind of conceptual arbitrariness to it. It’s like being told that certain facts can only be perceived from one spatial location—as it might be three feet away from the object—all the others being unsuitable for perceiving the object. One would like to see some sort of rationale for why the universe behaves this way. Why did God make pains perceivable only by the subject, and brains only perceivable by the outer senses? Why did he impose such tight rules on how perception of these things is possible?
Do the facts themselves dictate these rules? Compare mathematics: numbers are neither perceptible by the senses nor by themselves (the number 3 does not experience itself as odd). Plausibly, it is in their nature not to be so perceptible: they are abstract entities and hence not even candidates for perception in the ordinary sense. Might mental and physical facts be similarly unsuitable for a certain type of perception in virtue of their intrinsic nature? Perhaps pains as such are unsuitable for outer perception and brain states inherently unsuitable for inner perception. But if so, it can’t be because they are abstract, since they are concrete, i.e. spatiotemporal items with causal powers. So what is it about these things that renders them capable of perception by certain means but not others? There is no straightforward deduction from the nature of the mental and the physical to the conclusion that they can only be perceived in one way—by inner and outer sense, respectively. They can both clearly be perceived, unlike numbers, but they are limited in the ways they can be perceived. Pains are only too happy to be perceived by introspection (one might wish they would remain imperceptible) but they bluntly decline to be perceived by the outer senses; they just won’t go there. Similarly, physical properties reveal themselves to the senses quite freely, but they firmly resist the probing of the introspective faculty. Why this selectivity, this snobbery almost? Pains refuse to pass through the doors of (outer) perception, and brains won’t yield to introspective scrutiny: neither will join the other’s club. But there seems nothing about them considered in themselves that generates this exclusivity: both are concrete empirical phenomena existing in the real world. Yet they are extremely choosy about how they reveal themselves to the perceiving subject.
This is the way the universe has been constructed; it’s the way reality fundamentally is. We take it for granted because it’s so familiar to us: we don’t think scientists will discover tomorrow that pains can be seen or neurons introspected. It takes an intellectual effort to see this for the oddity that it is: how amazing that other people can’t see my pain! I can sense it in all its awful glory, but they are completely blind to it—for them it is just a dubitable conjecture (hence the problem of other minds). If they could see it that might change their attitudes, but they simply can’t—we mustn’t blame them. It would also be good if I could sense a tumor growing in my brain before it gets out of hand, but my powers of introspection are just not up to the task (“Why not!” I might exclaim angrily). Much philosophy has revolved around trying to avoid this puzzle (Wittgenstein being an arch-avoider), but really it is an inescapable feature of the given universe. And it adds yet another puzzle to an already long list.
 It’s hard to find a good verb that covers all cases of what is intuitively a basic type of awareness. I have chosen to use “perceive”, which is traditional: thus we perceive our pains (and other mental phenomena) as well as tables and rabbits.