Swampman
Lightning strikes a swamp and rearranges molecules into a perfect physical duplicate of a person, with no causal history. Does the resulting being have genuine thoughts?
Donald Davidson introduced this scenario in 1987 to argue that mental content is not determined by internal physical states alone. What a thought is about depends on the causal history connecting that thought to the world, and Swampman has no such history.
Davidson, D. (1987). Knowing One's Own Mind. Proceedings and Addresses of the American Philosophical Association, 60(3), 441–458.
The scenario
Davidson is walking through a swamp. Lightning strikes a nearby tree. By extraordinary coincidence, the bolt also strikes Davidson and kills him, while simultaneously rearranging the molecules of the tree into a perfect physical duplicate. Atom for atom, the duplicate is identical to Davidson.
This "Swampman" emerges from the swamp. It walks, talks, behaves exactly as Davidson would. It says things Davidson would say. It reacts to people Davidson knew as if it knows them. To all external observation, and to its own introspection, it seems to have all of Davidson's memories, beliefs, and personality.
Davidson's argument: Swampman has none of these things.
Davidson's argument: causal history is constitutive of content
The words Swampman utters do not mean anything, Davidson claims, because meaning requires the right kind of causal connection to the world.
When Davidson uses the word "tree," that word has its meaning partly because Davidson has interacted with trees, learned the word in contexts involving trees, and has a web of beliefs about trees formed through experience. The word is connected to the world by a causal chain.
Swampman has no such chain. Its internal states are arranged the same way Davidson's are, but they were not formed through interaction with anything. The sounds Swampman makes that look like the word "tree" were not caused by trees in the right way. They are not, strictly speaking, the word "tree." They are sounds that happen to resemble it.
The same goes for Swampman's "beliefs." They are functional states that look like beliefs from the outside. But mental content, what a thought is about, is not just a matter of internal organization. It requires the right causal history.
What Swampman is missing
The objection is immediate: from the inside, Swampman has everything Davidson had. It has what seems to be the memory of this morning's breakfast, the belief that it is standing in a swamp, the intention to get home. If those functional states feel like thoughts from the inside, in what sense are they not thoughts?
Davidson's reply is that "from the inside" is already begging the question. For there to be an inside, for there to be genuine mental states with content, the right causal connections must already be in place. Swampman may behave as if it has thoughts, but behavior is not the criterion.
This is a form of externalism about mental content: the content of your thoughts is not determined solely by what's in your head. It is partly determined by your history of causal interaction with the world.
The consequence is counterintuitive. Two beings physically identical in the present moment can have mental states with different content, or one can have mental states and the other none at all, purely because of facts about their past that are no longer visible in their current physical state.
Discussion questions
- If a perfect replica of you sprang into existence right now with all your memories, would it mean what you mean when it says things?
- Does meaning require causal history, or is it entirely in the present state?
- Is a Swampman's memory of childhood a real memory?
Take it to the dinner table.
Get 3 thought experiments for memorable conversations, designed for dinner, with friends, at events, or anywhere small talk has gone on too long.