We can see this in German, where one has interesting alternatives for constructing such identity-asserting sentences. Two examples follow, adapted from the German translation of a Stanislaw Lem dialogue in which an exact molecule-for-molecule replica of a doomed person is about to be constructed. In that spirit, we provide (nearly) exact word-for-word replicas in English of the German originals:
1. Ob die Kopie wirklich du bist, dafür muss der Beweis noch erbracht werden.
(As-to-whether the copy really you are, thereof must the proof still provided be.)
2. Die Kopie wird behaupten, daß sie du ist. (The copy will claim that it you is.)
Observe that in both identity-asserting clauses, “the copy” (or “it”) appears first, then “you,” then the verb. But notice—in the first clause, “are” is the verb, which retroactively implies that “you” was the subject and “the copy” was the complement, whereas in the second clause, the verb is “is,” retroactively implying that the subject was “it” and the complement was “you.” The fact that the verb comes at the end gives these clauses a sort of surprise-ending quality. In English we can’t achieve precisely the same effect comfortably, but we can ask for the difference in shades of meaning between the sentences “Is the copy really you?” and “Are you really the copy?” These two questions “slip” in our minds along different dimensions. The former slips into “Or is the copy really someone else—or perhaps no one at all?” The latter slips into “Or are you somewhere else—or are you anywhere?” Our book’s title, incidentally, can be construed not only as a possessive, but equally as a short full sentence reply to the two questions “Who am I?” and “Who is me?” Notice how the transitive usage—strictly speaking, an ungrammatical usage of “to be”—gives the second question a quite different “flavor” from the first.
[D.C.D. to D.R.H.: If I were you, I’d mention how curious it would be to preface some advice with “If you were me, I’d …” but if you were me, would I suggest that you mention it?]
All of these examples show how suggestible we are. We just fall like a ton of bricks for the notion that there’s a “soul” in there—a flamelike soul that can flicker on or off, or even be transferred between bodies as a flame between candles. If a candle blows out and is relit, is it “the same flame”? Or, if it stays lit, is it even “the same flame” from moment to moment? The Olympic Torch is carefully kept burning as it is carried by runners thousands of miles from Athens to its destination every four years. There is powerful symbolism to the idea that this is “the very flame that was lit in Athens.” Even the shortest break in the chain, however, would ruin the symbolism for people who knew. For people who didn’t know, of course, no harm done! How on earth could it possibly matter? Yet emotionally it seems to. It will not easily be extinguished, that “soulflame” notion. Yet it leads us into so much hot water.
We certainly intuit that only things of approximately the “same-sized souls” can slip into each other. The science-fiction story Flowers for Algernon by Daniel Keyes is about a retarded young man who by a miracle medical treatment slowly gains in intelligence and becomes a great genius—but then it turns out that the effects of the treatment cannot last, and “he” witnesses his own mental crumbling back into his retarded state. This fictional story has its counterpart in the real-life tragedy of people who, having grown from a state of zero mind to normal adult intelligence, witness themselves growing senile or who suffer serious brain damage. Can they answer for us the question “What is it like to have your soul slip out from under you?” any better than someone with vivid imagination can, though?
Franz Kafka’s Metamorphosis is the story of a young man who wakes up one morning transformed into a giant beetle. But the beetle thinks like a person. It would be interesting to combine the Flowers for Algernon idea with the Metamorphosis idea and imagine the experiences of an insect whose intelligence rises to the level of a human genius (why not superhuman, for that matter?), then sinks back to the insect level. Yet this is virtually impossible for us to conceive. To borrow electrical-engineering jargon, the “impedance match” of the minds involved is too poor. In fact, impedance match may well be the main criterion for the plausibility of questions of the form Nagel poses. Which is it easier for you to imagine being—the totally fictional character Holden Caulfield or some particular, actual bat? Of course it is much easier to map yourself onto a fictional human than onto a real bat—much easier, much realer. This is slightly surprising. It seems that Nagel’s verb “be” acts very strangely sometimes. Perhaps, as was suggested in the dialogue on the Turing test, the verb “be” is being extended. Perhaps it is even being stretched beyond its limits!
There’s something very fishy about this whole idea. How can something be something that it isn’t? And how is it rendered any more plausible when both things can “have experience”? It makes almost no sense for us to ask ourselves such questions as, “What would it be like for that black spider over there to be that mosquito trapped in its web?” Or worse yet, “What would it be like for my violin to be my guitar?” or “What would this sentence be like if it were a hippopotamus?” Like for whom? For the various objects concerned, sentient or not? For us the perceivers? Or, again, “objectively”?
This is the sticking-point of Nagel’s article. He wants to know if it is possible to give, in his own words, “a description [of the real nature of human experience] in terms accessible to beings that could not imagine what it was like to be us.” Put so starkly, it sounds like a blatant contradiction—and indeed, that is his point. He doesn’t want to know what it’s like for him to be a bat. He wants to know objectively what it is subjectively like. It wouldn’t be enough for him to have had the experience of donning a “batter’s helmet”—a helmet with electrodes that would stimulate his brain into batlike experiences—and to have thereby experienced “batitude.” This would, after all, merely be what it would be like for Nagel to be a bat. What, then, would satisfy him? He’s not sure that anything would, and that’s what worries him. He fears that this notion of “having experience” is beyond the realm of the objective.
Now perhaps the most objective-sounding of the various synonyms earlier listed for BAT-itude is “having a point of view.” After all, even the most dogmatic of disbelievers in machine intelligence would probably begrudgingly impute a “point of view” to a computer program that represents some facts about the world and about its own relationship to the world. There is no arguing with the fact that a computer can be programmed to describe the world around it in terms of a frame of reference centered on the machine itself, as in this: “Three minutes ago, the Teddy bear was thirty-five leagues due east of here.” Such a “here centered, now-centered” frame of reference constitutes a rudimentary “egocentric” point of view. “Being here now” is a central experience for any “I.” Yet how can you define “now” and “here” without making reference to some “I”? Is circularity inevitable?
Let us ponder for a moment on the connection of “I” and “now.” What would it be like to be a person who had grown up normally, thus with ordinary perceptual and linguistic capacities, but who then suffered some brain damage and was left without the capacity to convert the reverberating neural circuits of short-term memory into long-term memories? Such a person’s sense of existence would extend to only a few seconds on either side of “now.” There would be no large-scale sense of continuity of self—no internal vision of a chain of selves stretching both directions in time, making one coherent person.