by Carl Pierer
After having presented Clark and Chalmers' extended cognition hypothesis as well as two lines of argument against the hypothesis, the last article at this place ended with an intuitive, bad gut-feeling and a promise to develop this feeling into a full blown argument. Before making good on that promise, this article will start with a brief recap of the arguments presented so far.
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Clark and Chalmers' argue in their famous “the extended mind” paper that when a person uses tools or the environment to facilitate a particular cognitive process, this person and her tool constitute a coupled system. Indeed, Clark and Chalmers suggest that in such a coupled system the cognition extends, i.e. it is not confined to the brain/skull-boundary. The argument works as follows: suppose the cognitive process in question is to decide whether a certain shape that appears on the screen will fit into a given slot (as in the classic Tetris game). The person can use a computer to rotate the shape and decide whether it will fit or not. Now, this is clearly an external process. But imagine that in the not so far future, a person will have a neural implant with exactly the same functional structure as the computer and she can use the implant to rotate the shape and check whether it will fit (or she can use the traditional method of rotating it mentally). Clark and Chalmers think that as there is no difference between the computer and the neural implant. Further, whether the person in the near future choses the implant or the traditional method does not matter for the process to count as cognitive. Therefore, the only thing that distinguishes the computer-scenario from the neural-implant-one is that the former involves the use of a tool external to the brain/skull-boundary. But since precisely this is at question, this difference cannot be invoked to support the claim that using the computer is non-cognitive. Thus, using the computer is cognitive and so cognition extends.
Clark and Chalmers' argument relies on the parity principle:
If, as we confront some task, a part of the world functions as a process which, were it done in the head, we would have no hesitation in recognizing as part of the cognitive process, then that part of the world is (so we claim) part of the cognitive process.
This seems to follow directly from the basic functionalist idea that what it takes for a process to count as cognitive is its functional structure, rather than its physical instantiation.
In the previous article, two lines of argument against this view were presented. The first is taken by Adams and Aizawa. They suggest that any process that is to count as a cognitive process has to bear the “mark of the cognitive”. They think that it is not theoretically impossible for cognition to extend, but as a contingent matter of fact there is no process involving the external world that bears the mark of the cognitive. It was mentioned in passing that their suggested “mark” is closely modelled on human cognition. The second line is taken by Sprevak, who argues that the hypothesis of extended cognition provides a counterargument to the view from which it is derived, i.e. functionalism. He attacks Adams and Aizawa's argument on the grounds that their “mark of the cognitive” is too closely modelled on human cognition and deny processes to be cognitive on the grounds of being instantiated differently – a violation of the basic functionalist idea. At the same time, he suggests that functionalism entails extended cognition and further that a moderate (Clark and Chalmers') version of extended cognition is impossible. Instead, if functionalism is accepted the conclusion that any process is cognitive follows.

