Skepticism and Self-Knowledge
From the point of view of skepticism, self-knowledge is an anomaly. How is it that facts about a person’s psychology can be known with certainty when everything else is uncertain? It’s not as if first-person ascriptions of mental states are analytic or a priori; they report the same facts as give rise to the skeptical problem of other minds. We might think of this as the puzzle of first-person infallibility: how come we can’t be wrong about our own inner lives when we can be wrong about everything else? Of course, not everyone has accepted that we are thus infallible, even about whether one is in pain, but I think they fail to appreciate the force of the anti-skeptical position in this area; in any case, I will not attempt here to parry these assaults on introspective certainty. Instead I will offer a mixed position that accepts the standard claim of infallibility but finds one place at which the infallibility breaks down—so that such beliefs are not completely infallible, though they are largely so. General skepticism does not then run into an outright counterexample: all (empirical) knowledge is fallible one way or another.
So suppose I am in considerable pain as a result of stubbing my toe. I judge this to be so, uttering the words, “That hurts!” Could I be wrong? There are two places at which possible error might be supposed to creep in: with respect to the type of sensation I am feeling, and with respect to who has that sensation. Could I really be feeling another sensation altogether and misidentify it as pain—say, a pleasant sensation or a sensation of red? I could of course use the wrong word to describe my sensation (perhaps my English is shaky or I have some sort of language pathology), but that doesn’t mean that I misapply the concept of pain. I would agree with those who insist that no such thing is possible: I couldn’t be feeling a sensation of pleasure or a sensation of red and mistakenly suppose it to be a sensation of pain. I can’t misidentify my sensations in this way: I know with certainty what kind of sensation I am having—I feel that sensation directly and I apply the correct concept to it. What about the identity of the person feeling pain—could I misidentify him? I know that somebody is in pain and I mistakenly take that person to be me (actually it’s the person sitting opposite me). That again looks like a rank impossibility: I can’t judge that someone is in pain and wrongly suppose that I am that person. If I judge that I am in pain, I must be right about the identity of the sufferer: I know for sure that it is I who is in pain. Thus I cannot be informed that I am in pain once I have judged that someone is: I know it’s me just by knowing my own pain, unlike knowing (say) that someone in this room has won the lottery and being informed that it’s me. The pain presents itself as mine when it is mine. It is as if the pain has a little sticker on it saying, “This belongs to you”. Taking these points together, then, there seems no room for error in the self-ascription of pain: both possible points at which error might occur are blocked, so I know infallibly that I am in pain. I could never believe that I am in pain when I am really seeing red, or that I am in pain when it is really the person opposite me. By contrast, I could believe that my house is on fire when really it is merely well illuminated, or when it’s the next-door neighbor’s house that is in flames not mine.
So far, then, the case of self-knowledge is not parallel to the case of knowledge of the external world (or other minds). But there is one point of potential fallibility that we have not explored—the time of the pain. For I do not merely judge that I am pain at some time but at this time—I judge that I am in pain now. Could I be wrong about that? Could I misidentify the time of the pain? In particular, could a past pain be mistakenly attributed to the present time? Philosophical astronomers are fond of pointing out that the light reaching us from distant galaxies might have originated from a source that is now very different from what it was when the light departed from it, and might not now even exist. We have the impression that the object of sight is now as it seems to be, but that may not be so—and it is often not so. If we judge that that object is now thus and so, we make a mistake; rather, it wasthus and so. There is a time lag between when the light started out and when it reaches our eye, and this time lag can produce erroneous temporal belief. For instance, what looks like a contemporaneous stellar explosion could have occurred long ago. Taking a cue from this case, let us imagine a mind that is spread out across the universe at a scale of billions of miles: the brain that serves this mind is distributed as widely as galaxies are. In one part of it sensations of pain are processed, while in another part beliefs are processed, specifically beliefs about pain. Suppose it takes many years for signals from one part of this distributed brain to be received by the other part. Then the person whose brain this is may judge that he is in pain now when in fact the pain ceased long ago, say two centuries ago. He is quite correct to suppose that pain occurred in him but he gets the time of its occurrence wrong (we may suppose that he doesn’t know about the time lag). He thinks he is in pain now but in fact he isn’t. He makes temporal errors in his self-ascriptions of pain (as well as beliefs, emotions, etc.).
Now the skeptic sees his opportunity: couldn’t the human brain be subject to a similar time lag? In fact it is: it takes time for nerve signals to travel from the pain centers of the brain to its cognitive centers (located in the frontal lobes). It may be that by the time you judge that you are in pain the pain has receded, though no doubt you are usually still in pain at the time that you judge you are. The skeptic will then conjure the possibility, based in neurophysiological fact, that in any case of self-ascription of pain it is possible that the pain has ceased by the time you judge it to exist. You judge that it exists now, simultaneously with the judgment, whereas in fact it existed at a previous time, possibly a few milliseconds earlier or even months ago (maybe your brain is extremely slow). Perhaps you have been hooked up by a super scientist so that there is a time lag of five minutes between having a mental state and judging that you have it, so that all your self-ascriptions are false with respect to time (assuming the mental states don’t persist till the moment you make the judgment). Thus self-ascriptions of mental states are fallible, we might now be systematically making mistakes about the time of our mental states, and skepticism extends to self-knowledge (at least in this one respect). Nothing is therefore completely immune from skepticism; error is always possible (with regard to the empirical world anyway).
The reason that error is always possible is that fact and belief do not necessarily coincide. It is thus possible to believe that something is happening now that is not happening at that time: I might think that a certain lecture is happening now but in fact it happened an hour ago; likewise I can think that a pain is happening now but in fact it happened a second ago. There is the fact on the one hand and there is the judgment about it on the other. This division is as true for mental states and self-ascriptions of them as it is for anything else, so it is not surprising that error is possible here too; what is surprising is that it is confined to the temporal content of such judgments, having no parallel with respect to the identity of the state ascribed and who it is ascribed to. I can’t be wrong about what state I am in and about it being I that is in it—but I can be wrong about when the state occurs. I know for sure there has been pain in my life, but exactly when is subject to skeptical doubt. Maybe all my pain happened years ago and I am only now getting round to self-ascribing it: it just takes that long for the fact to make itself known to my introspective faculty. And the same is true of it seeming to me that I am in pain: this too could precede the act of judging that it so seems to me. The neural correlates of pain actually do precede the neural correlates of judging that you are in pain, granted that the relevant signals have to travel across the cortex in a finite time, so there is always a bit of a lag time between fact and report. The skeptic simply amplifies this point to construct fanciful scenarios that dramatize the gap between fact and judgment. So we should add to the usual brain-in-a-vat case what might be called the brain-in-a-time-lag case.
 It is of course equally true that there is a lag between the time a stimulus leaves an external object and the time we have a perception of that object, which is particularly noticeable in the case of sound. This implies the possibility of error about the time of external events, as when you think that thunder (the physical phenomenon) occurs at the same time you hear it. Everything outside us thus happens slightly earlier than when we perceive it and make the corresponding judgment. It turns out that the same is true of events in one’s mind and judgments about them, which opens the case up to skepticism.