Introducing the Extended Mind Thesis: Can the Mind be Extended Beyond the Skull?

The mind, and consequently where it exists, has been a key issue in the philosophy of mind. Traditionally, many had believed that the mind exists only in the body, adhering to “the demarcation¹ of the skin and the skull”. However, Andy Clark and David Chalmers argued in a 1998 paper that the mind could extend beyond the body when certain external objects serve as part of the mind². In this brief essay, I introduce their thesis, lay out their arguments, discuss their famous thought experiments, bring out a counterargument and a reply to the counterargument, before concluding on the thesis’s importance and implications.

In Clark and Chalmers’s paper “The Extended Mind”, they argue that an external object could serve as part of the mind if it performs a task or occupies a role that we would happily call cognitive had it been done in the mind and if the internal mind and the external object are in a reliable, easily accessible, action-guiding coupled system. They raise the classic example of Otto and Inga. While for Inga, her memory tells he which street to go to for a certain museum exhibition, a notebook for Otto, who suffers from Alzheimer's, does the same thing. Naturally, Inga’s memory is part of her mind, and we also tend to think that Inga has a belief with respect to the museum’s location, a belief that persists even when she does not consult her memory (e.g. her belief does not disappear when she is asleep). But then, it seems that there are no meaningful differences that could suggest why the notebook, being constant in his life, directly available, automatically trusted, and normally used when relevant, is not part of Otto’s mind; while one can point to the fact that the notebook is outside the body (and the brain), this boundary of the skin/skull is exactly the claim that is being contested, and thus it would beg the question to cite it for support. And while Otto may be unable to consult his notebook when he cannot read it in the dark, the same is true for Inga, and for both of them the belief does not come and go – in fact, what really counts is just that both are able to access the information at times when it is useful. As Clark and Chalmers have argued, Otto is on par with Inga, and the information in the notebook is part of Otto’s mind.

One may quickly object that an external object simply being causally coupled to a cognitive agent does not mean that the object is part of the mind; indeed, as Adams and Aizawa objected, many objects, like books, calculators, teachers, maps, and screens play important cognitive roles, and yet we do not tend to think that these objects are part of our minds³. While Clark later accepted that mere coupling is not enough, he also pointed out that even initially the argument was not supposed to suggest simple coupling. Instead, the Extended Mind Thesis is closer to a parity principle under limiting conditions: if an objects constantly, reliably provides a directly available function that is used automatically, undoubtedly in the same way that the mind (or part of it) does, refusing to count it as cognitive merely because it is outside the skull begs the question.

Another objection, the cognitive bloat objection, raised by Robert Rupert, argues that allowing Otto’s notebook to count as part of his mind makes it difficult to stop from expanding too far⁴. Why not say that a person with constant internet access believes millions of facts stored on Wikipedia or Google? Why not say that my phone, laptop, books, and search engine results are all parts of my mind? These seem to be out of my mind even if they can be reliably accessed and even if someone (who is unwise enough) wholly trusts Google or Wikipedia, and yet it may be difficult to draw a boundary between these and Otto’s notebook if the latter is treated as part of the mind. Three replies exist: for one, the Extended Mind Thesis, as aforementioned, includes qualifications, and Clark and Chalmers explicitly say that the internet will usually fail unless someone is unusually reliant on and trusting of it; for another, skipping from a difficult line to no line at all is absurd, for there are always things that are certainly on one side of it⁵; finally, it may actually be the case that something analogous to wikipedia part of a person’s mind -- if technological innovations like Neuralink⁶ enables constant access to a trusted AI agent, then why not?

In conclusion, “The Extended Mind” presents the thesis that the mind can go beyond the boundary of skin and skull. While important qualifications must be added to ensure that the thesis does not incorporate cases when it shouldn’t, the general validity of the thesis serves as an important note not only for the philosophy of mind and the cognitive sciences but also for moral philosophy and legal jurisprudence. On the one hand, it may be more than a destruction of property to burn Otto’s notebook; interfering with the notebook or perhaps influencing someone’s environment in cases like Otto’s may instead be viewed with the same moral significance as interfering with their moral personhood. On the other hand, certain forms of social activity might not be categorized as action but rather as thought, which may also change their moral category and even influence judgments of moral permissibility. Regardless, as Clark and Chalmers wrote, “once the hegemony of skin and skull is usurped, we may be able to see ourselves more truly as creatures of the world.”