Building a Second Brain

Cognitive research on working memory has settled on a smaller number than most people expect. Rather than the seven items often quoted from older studies, more recent work finds the reliable capacity is closer to three or four distinct pieces of information at once, before accuracy and processing speed start to drop noticeably.

David Allen's phrase, “Your mind is for having ideas, not holding them,” captures the logic behind external systems for organising information. Tiago Forte develops a related idea in Building a Second Brain, arguing that digital tools can help people capture, organise and retrieve knowledge rather than relying on memory alone.

It turns out to have a fairly precise number behind it rather than just being a nice turn of phrase. I used to treat forgetting something as a personal failing, evidence I wasn't organised enough or didn't care enough to remember.

Three or four items is not a large working surface. I was routinely asking mine to hold twelve.

A second brain, a notebook, an app, any external system that holds what your working memory physically can't, isn't a shortcut around thinking. It's matching the task to the actual size of the tool doing it. The need for an external memory is not new. It appears in the notebook beside a writer's bed, the screenshots saved for later and the folder of links that someone promises to revisit.

I used to feel a quiet embarrassment about needing the notebook at all, as though a sharper mind wouldn't require the backup. Three or four honest slots were never the flaw I took them for.

I still catch the old embarrassment occasionally, quickly followed by the reminder that the number was never really mine to argue with. I stopped apologising for the notebook a while ago.

It isn't a crutch. It's closer to giving three or four honest slots the room they were always going to need to do their job properly.