When we jot something down—a shopping list, maybe—on a piece of paper, aren’t we in effect remembering it outside our heads? Most of all, isn’t language itself something that’s always external to the individual mind? We can’t invent our own private languages; as Wittgenstein showed in his Philosophical Investigations, we can invent our own words for things, but only as substitutes for words that already exist; it’s impossible to make the incommunicable meaningful. Language sits hazy in the world, a symbolic and intersubjective ether, but at the same time it forms the substance of our thought and the structure of our understanding. Isn’t language thinking for us?

This is not, entirely, a new idea. Plato, in his Phaedrus, is hesitant or even afraid of writing, precisely because it’s a kind of artificial memory, a hypomnesis. (Incidentally Freud inverts the metaphor 2,000 years later: The unconscious mind is like a child’s toy, the Mystic Writing Pad.) Writing, for Plato, is a pharmakon, a “remedy” for forgetfulness, but if taken in too strong a dose it becomes a poison: A person no longer remembers things for themselves; it’s the text that remembers, with an unholy autonomy. The same criticisms are now commonly made of smartphones. Not much changes.

Most of all, though, a theory similar to extended cognition is present in the work of Hegel and his descendants—and, in particular, Marx. In the dialectical tradition, the hermetic and self-contained Cartesian consciousness is impossible: We only become conscious in and through the world and its history. Marx, in the Economic and Philosophic Manuscripts of 1844, describes the process of unalienated labor in familiar terms. “The object of labor is, therefore, the objectification of man’s species life: for he ... contemplates himself in a world that he has created.” Work, without ownership or scarcity, is a kind of play: You’re always turning the exterior world into something else, something more responsive to your needs and your being. In a liberated future, the world of objects can be an externalization of our own consciousness; it can be a true home for humanity, because it is already ourselves. But not yet; first we have to overthrow capitalism. In the 20th century, Theodor Adorno picks up this theme: The “separation between subject and object” exists—I am not the world around me, in fact for the most part I’m terrified by it while it’s monstrously indifferent to me—but this is “the result of a coercive historical process.” It wasn’t always this way, it doesn’t have to be forever. The difference is that, according to theories of extended cognition, this separation is already over and always was, that subject and object are united right now.

But not entirely. Extended cognition promises to rip up the idea of a mind that lives only in the furrows of the brain, but it doesn’t always follow through. Cognition is extended, outsourced, leaking from cranial slime into the material world—but like an octopus’s tentacle, it can always dart back in. There are stranger and more dangerous possibilities. Take the grocery list. For Clark and Chalmers, it’s a brain process—information storage and retrieval—offloaded onto a piece of paper. But by whom? In Limited Inc, Jacques Derrida uses the same object to construct a very different interpretation. “At the very moment ‘I’ make a shopping list,” he writes, “I know that it will only be a list if it implies my absence, if it already detaches itself from me in order to function beyond my ‘present’ act and if it is utilizable at another time, in the absence of my being-present-now.” The list will still do its cognitive work if you are not currently reading it. The list will still do its work if you are dead. If we can accept that a grocery list is in some way thinking, is the part of the mental apparatus that remains lodged in the human brain really so central? The thought-capacity of objects is indifferent to whichever bit of brain is plugged into it. A war memorial remembers its list of the dead for us, in the same way that a scrap of paper remembers milk, and it keeps remembering, long after the weeds have grown and the rest of the world has tumbled past caring.