Swampman Meets a Cow-Shark

[32. SWAMPMAN MEETS A COW-SHARK]

Intuition pumps are supposed to work cleanly and efficiently, pumping the sought-for intuition and then going back into storage. But a common fate of intuition pumps is to inspire a frenzy of rebuttal, counter-rebuttal, adjustment, and extension. Donald Davidson, one of America's best twentieth-century philosophers, once told me that he regretted inventing this intuition pump, since it instigated such an excessive and only intermittently illuminating wrangle. Here is Swampman, one of philosophy's favorites—if not Davidson's (1987):

Suppose lightning strikes a dead tree in a swamp; I am standing nearby. My body is reduced to its elements, while entirely by coincidence (and out of different molecules) the tree is turned into my physical replica. My replica, The Swampman, moves exactly as I did; according to its nature it departs the swamp, encounters and seems to recognize my friends, and appears to return their greetings in English. It moves into my house and seems to write articles on radical interpretation. No one can tell the difference.

But there is a difference. My replica can't recognize my friends; it can't recognize anything, since it never cognized anything in the first place. It can't know my friends' names (though of course it seems to); it can't remember my house. It can't mean what I do by the word "house," for example, since the sound "house" it makes was not learned in a context that would give it the right meaning—or any meaning at all. Indeed, I don't see how my replica can be said to mean anything by the sounds it makes, nor to have any thoughts. [pp. 443–444]

It cannot have escaped philosophers' attention that our fellow academics in other fields—especially in the sciences—often have difficulty suppressing their incredulous amusement when such topics as Twin Earth and Swampman are posed for apparently serious consideration. Are the scientists just being philistines, betraying their tin ears for the subtleties of philosophical investigation, or have the philosophers lost their grip on reality? I'd rather (hint) not say.

These bizarre examples attempt to prove one conceptual point or another by deliberately reducing all but one underappreciated feature of some phenomenon to zero, so that what really counts can shine through. The Twin Earth example sets internal similarity to a maximum (you are whisked off to Twin Earth without being given a chance to register this huge shift) so that external context can be demonstrated to be responsible for whatever our intuitions tell us. The Swampman intuition pump keeps both future dispositions and internal states constant and reduces "history" to zero. Thus these thought experiments mimic scientific experiments in their design, attempting to isolate a crucial interaction between variables by holding other variables constant. A problem with such experiments is that the dependent variable is intuition—they are intuition pumps—and the contribution of imagination in the generation of intuitions is harder to control than philosophers have acknowledged. (Several of the boom crutches we will dismantle actually suppress the imagination of readers, distorting their intuitions and thus invalidating the "results" of the thought experiment.)

But there is also a deeper problem with such experiments. It is child's play to dream up examples to "prove" further conceptual points. Suppose a cow gave birth to something that was atom-for-atom indiscernible from a shark. Would it be a shark? If you posed that question to a biologist, the charitable reaction would be that you were making a labored attempt at a joke. Or suppose an evil demon could make water turn solid at room temperature by smiling at it; would the demon-water be ice? This is too silly a hypothesis to deserve a response. Smiling demons, cow-sharks, zombies, and Swampmen are all, some philosophers think, logically possible, even if they are not nomologically (causally) possible, and these philosophers think this is important. I do not. Presumably the motivation for casting the net of counterfactuality so wide is so that the answer we retrieve will tell us about the essence of the topic in question. But who believes in real essences of this sort nowadays? Not I.

Consider a parallel question we might ask about magnets, after we noticed that there were competing candidates for the "truth-maker"—the defining property or essence—for magnets: (a) all magnets are things that attract iron, and (b) all magnets are things that have a certain internal structure (call it M-alignment). Was the old, behavioral criterion (a) eventually superseded by the new, internal structure criterion (b), or did the latter merely reductively explain the former? To find out, we must imagine posing scientists the following Swampman-style questions. Suppose you discovered a thing that attracted iron but was not M-aligned (like standard magnets). Would you call it a magnet? Or: Suppose you discovered a thing that was M-aligned but did not attract iron. Would you call it a magnet? The physicists would reply that if they were confronted with either of these imaginary objects, they would have much more important things to worry about than what to call them. Their whole scientific picture depends on there being a deep regularity between the alignment of atomic dipoles in magnetic domains and iron attraction, and the "fact" that it is logically possible to break this regularity is of vanishing interest to them. What is of interest, however, is the real covariance of "structural" and "behavioral" factors. If they find violations of the regularities, they adjust their science accordingly, letting the terms fall where they may.

Does Swampman have thoughts and speak English, or not? Is a cow-shark a shark? It swims like a shark, and mates successfully with other sharks. Oh, but didn't I tell you? It is atom-for-atom indiscernible from a shark, except that it has cow DNA in all its cells. Impossible? Not logically impossible (say the philosophers). Just so obviously impossible as to render further discussion unenlightening. It is just as clearly physically impossible for the "traces" of, say, Davidson's memories to appear in the structure of Swampman's brain as it is for a shark to form itself of cells containing cow DNA. Swampman may not be logically impossible, if only because cosmic coincidences of the sort imagined to produce things like Swampman are by definition not logically impossible, but they never happen, so who cares what we would say if they did?

"I do," says the philosopher who is on the lookout for rhetorical questions. "I think it is important always to define your terms with utmost rigor, covering all logically possible eventualities. That's the way to get to the truth." But is it? In the real world, past history and future function are bound together by multi-stranded cables of evolution, development, and learning. It is because Davidson's body had taken the particular trajectory that it did for years on end that Davidson had all those memories and beliefs and projects, and there is no real substitute for these natural accumulation processes. Settling the verdict on imaginary cases that violate these conditions serves no purpose that I can see. In fact, such labored examples strike me as manufactured opportunities to impose an imaginary dichotomy so that you can rather with impunity. "No," says the philosopher. "It's not a false dichotomy! For the sake of argument we're suspending the laws of physics. Didn't Galileo do the same when he banished friction from his thought experiment?" Yes, but a general rule of thumb emerges from the comparison: the utility of a thought experiment is inversely proportional to the size of its departures from reality.

Twin Earth is physically impossible, but not as impossible as Swampman! (Don't think that the many-worlds interpretation of quantum mechanics, which is gaining favor in some quarters, shows that Twin Earth is physically possible after all; even if there are an infinity of universes "out there" including (infinitely?) many that have planets that are almost like Earth, we can't send an earthling to any of them for a visit.) The two-bitser's trip to Panama, in contrast, is not just possible; instances of it may well have happened. We don't have to suspend any laws of nature to imagine it in whatever detail we like.