The extended mind was always personal
Steven Johnson has spent his career on what he calls tools for thought, and one of the more interesting ones to arrive lately is the research assistant he helped Google Labs build, NotebookLM. In July, Google dropped the “LM” and folded it into the wider brand as Gemini Notebook. Johnson used the occasion to write, in his Adjacent Possible newsletter, about why the tool works at all, and he reached for a piece of philosophy to explain it: the extended mind.
The idea comes from a short 1998 paper by the philosophers Andy Clark and David Chalmers, “The Extended Mind,” published in the journal Analysis. Their argument runs through a character named Otto. Otto has Alzheimer’s, so he keeps a notebook of everything he needs to remember, and he carries it everywhere. When he wants to get to the museum, he looks up the address he once wrote down, the same way you would pull it from memory. Clark and Chalmers make the radical claim that the notebook is not a stand-in for Otto’s memory. It is his memory, literally part of his mind, running on paper instead of neurons. Johnson’s point is that a notebook you can talk to, one that reads your sources alongside you, is the most literal version of Otto’s notebook anyone has built. I think he’s right, and the tool is good. I also think the argument has a second half he doesn’t mention, the half that applies to teams and companies rather than to individuals.
The extended minds that last are personal
Look back at the whole lineage and one feature holds all the way through. The Renaissance commonplace book, a personal volume where a reader copied out the passages worth keeping. The diary. The box of index cards a scholar spent decades filling. Otto’s notebook. Now NotebookLM. Every one of them is a single person’s, curated by hand, and useless to anyone except the one keeping it.
That isn’t a flaw. It’s the reason they work. Otto’s notebook is reliable because Otto tends it, corrects it, and trusts it the way he trusts his own recall. NotebookLM is powerful for the same reason: you choose the sources, you decide what goes in, and the model reasons over a corpus you assembled on purpose. The curation is the value. An extended mind you didn’t shape wouldn’t be an extension of your mind at all.
So the personal extended mind is a solved problem, and Johnson’s tool is about as good a version of it as exists. The trouble starts when you try to make one for more than one person.
No one keeps the company notebook
Every team accumulates knowledge about how it actually runs. What they told that customer last week, why the launch date moved, which of them knows how the billing edge case works. The instinct is to do for the team what Otto does for himself: keep a notebook. Stand up a wiki. Start a shared drive. Point everyone at the same NotebookLM.
It never lasts. The wiki is accurate for a month and stale for a year, until someone gets a bee in their bonnet and fixes it, and then it starts rotting again. The shared drive becomes a place files go to be lost. Not because people are lazy, but because the model that makes a personal extended mind work is exactly what can’t scale. Otto’s notebook stays current because one person owns it. A company notebook’s upkeep belongs to everyone, which means it belongs to no one. That’s a free-rider problem: everyone draws on the notebook and nobody bears the cost of keeping it, so nobody does. A mind nobody is keeping isn’t an extended mind. It’s an archive, and a rotting one.
I got a firsthand education in what an organization does instead. My first month at Facebook was spent in Bootcamp, the engineering onboarding everyone went through, working real tasks against real systems. Most of those tasks required learning something new or digging up some details and sample code, and finding a single source of truth was hard enough that I drew a conclusion about the place: it had an oral culture, not a written one. There was no shortage of text. But you weren’t expected to discover things on your own. You were expected to know who to ask, and half of onboarding was building your network.
That is what a company does when the written record can’t be trusted. It doesn’t stop functioning. It routes around the gap by keeping the knowledge in people’s heads and moving it by conversation, which works fine as long as the experts are still there and have time for you. The cost never shows up in a budget. Every answer spends two people’s attention instead of one person’s search. Every departure takes part of the record out the door, and there is a number for how much: a 2018 Panopto survey of 1,001 employees at companies of 200 or more people found that 42% of what a company knows is known by one person only.
You can throw people at the gap. Big companies do. They pay someone to keep the CRM clean and someone to write the status update that spreads what changed. What that buys is a team fighting entropy by hand, staying a step ahead of fragmentation. It never becomes a system that keeps itself. Hand-curation was always the mechanism, and hand-curation is precisely what doesn’t survive contact with a group.
A collective mind has to assemble itself
This is the problem my company works on, so what follows is an interested view; the fully self-maintaining version is a pilot, not a shipped product.
A knowledge base that keeps itself current has been a dream for as long as we’ve had wikis. It never arrived because upkeep was the one part no tool could take over. What’s changed is that the tending, reading a stream and keeping a record consistent with it, is now the kind of work a model can do. And much of the material it needs is already there, produced just by the work itself. The knowledge of how the place actually runs is moving through its email, its chat, and its meetings every hour of every day. Nobody has to sit down and write it into a notebook, because the team is already writing it, to each other, in the course of doing the work.
If a collective extended mind is possible, that is the shape it takes. Not a notebook you write in, which is the individual pattern and doesn’t survive being shared. A record that builds itself from the stream of messages the team is already sending. The upkeep problem that kills every wiki changes shape: there is no writing step, only a checking one, and checking is the cheaper of the two. The maintenance is a byproduct of everyday activity.
The notebook framing can’t make this move, and it shouldn’t try. A personal tool should be personal. Otto’s notebook would be worse, not better, if it tried to fill itself from everyone’s calendars. The collective case is a different problem with a different answer, and it opens up right where the individual one runs out.
The catch worth naming
A mind that builds from messages needs the messages to accumulate before it knows much. It starts closer to empty than a notebook you have spent a year curating, and it earns its accuracy over weeks of real traffic rather than on day one. The bet is that automatic, even from a slow start, ends up ahead of diligent-by-hand, because diligence at team scale is what always slips.
Johnson is right that the extended mind is the frame for all of this. Otto’s notebook, the commonplace book, NotebookLM: that lineage holds and it is still being extended. The part still open is the collective one, and you cannot get there by handing everyone a better notebook. You get there with a mind the team doesn’t have to build from scratch or maintain.