Swampman

The experiment runs as follows:[2]

Suppose lightning strikes a dead tree in a swamp; I [Davidson] 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.

— Donald Davidson, Knowing One's Own Mind

These considerations lead Davidson to deny that the Swampman's utterances can be construed as referring to anything in particular. To take a fairly specific example, suppose that at some point the previous day Davidson had looked at a glass marble on a shelf; unbeknownst to him there was another, visually identical, glass marble hidden right behind it. When he makes an assertion about "the marble I saw yesterday", we take him to be referring to the one that he did in fact see, even if he could not supply enough descriptive information to identify it later. Had the marbles been arranged in the other order, therefore, we would take him to be referring to the other marble, yet his internal state would be identical.

The Swampman has no causal history. He is in the same state as the actual Davidson and the counterfactual Davidson considered above, whose utterances refer to different marbles. As a result, his utterance could refer to either marble. In principle, Davidson tells us, the above indeterminacies can be extended to any degree we like: the fact that the Swampman happens to be identical to Davidson does not change the fact that he could have arrived at that state by any one of countless histories, each of which would demand we interpret him differently. Until the Swampman has begun interacting with and using language among the objects of the real world, we can have no grounds to attributing any meanings or thoughts to him at all.

Amongst those who accept the force of this argument, there are two distinct ways of viewing its consequences. On the one hand, many philosophers have taken it to affect merely how we should evaluate Swampman. The argument is believed to demonstrate that Swampman's utterances and thoughts do not mean anything, and do not refer to anything in particular. On this view, Swampman's subjectivity and consciousness are considered to be unchanged. Others have argued that this lack of a causal history renders incoherent the notion that Swampman could have a mind at all, which in turn raises the question of whether he is, in fact, a person (note that Davidson calls Swampman "it" rather than "he").

This argument depends upon the acceptance of semantic externalism, the claim that the meaning of one's words is determined not merely by some internal state, but also by the causal history of the speaker. A thought experiment somewhat similar to Swampman is in Ibn Tufail's novel Hayy ibn Yaqdhan, where a child is spontaneously generated and later turns into a philosopher. It is also similar to the philosophical zombie argument.

This concept has been said to have implications for mind uploading or mind transference, as it indirectly addresses the question of whether an exact replica of one's brain patterns, created within an alternative brain, an android brain, or a virtual universe, is the same being as the person it was copied from, or another being entirely. The same question is to be considered if a technology to teleport people arises.

• Davidson, Donald (2001 (1987)). "Knowing One's Own Mind" Reprinted in Subjective, Intersubjective, Objective (pp. 15–38). New York and Clarendon: Oxford University Press. Originally published in Proceedings and Addresses of the American Philosophical Association, 60 (1987), 441–58.'