The Commonplace Cartographer: How John Locke Indexed His Mind

Before digital tags and bidirectional links, before the promise of a second brain, there was a man with a quill, a pot of ink, and a profound desire to map the territory of his own reading. In 1685, while taking a brief respite from drafting his monumental works on government and human understanding, John Locke devised a method for commonplacing that was, for its time, nothing short of revolutionary. He wasn't just collecting quotes; he was building a responsive index to the contents of his own mind.

Locke’s system, which he detailed in a letter to a friend and which was later published as "A New Method of Making Common-Place-Books," solved a problem that feels remarkably contemporary: how do you find something again once you’ve filed it away? The traditional method of commonplacing—jotting down excerpts under broad, pre-defined headings like "Virtue" or "Politics"—was, to Locke, fundamentally flawed. If you encountered a brilliant passage on the fallibility of kings while reading a history of Rome, where should you put it? Under "Monarchy"? "History"? "Fallibility"? The original context could be lost forever in the wrong drawer.

His solution was elegantly simple and profoundly clever. He abandoned alphabetical order for the subjects themselves. Instead, he indexed the index. Each two-page spread in his commonplace book was assigned a unique number. After transcribing a passage onto a page, he would create an entry for it in an alphabetical index at the back of the book. But here was the genius: he didn't just list the subject. He would break the subject down into its smallest constituent parts. That passage about a Roman king might be indexed under "Kings," "Rome," "Corruption," and "Power." Each of these index entries would point back to the same page number.

This is the quiet ancestor of our hashtags and our multi-linked notes. Locke’s method allowed for emergent, bottom-up categorization. The structure of his knowledge wasn’t predetermined by a rigid taxonomy; it grew organically from the material itself, connected by a web of cross-references. He was, in effect, creating a primitive database, enabling him to traverse his collected thoughts along multiple associative pathways. To look up "Power" was to potentially stumble upon reflections from theology, political theory, and personal observation, all in conversation with one another.

There’s a lesson here for us, swimming in our oceans of digital clippings and endless open tabs. We often spend more time searching for the perfect, all-encompassing system—the app that will finally organize our chaos—than we do developing a simple, consistent method for retrieval. Locke’s breakthrough wasn't a piece of technology; it was a principle. It was the understanding that the true value of a note lies not just in its content, but in the number of doors that open onto it. He wasn't just storing information; he was ensuring it could be found again, from any angle his future mind might approach it. In an age of intellectual superabundance, perhaps the most radical act is not to capture more, but to build a better, more personal map for what we already hold.

Notes & further reading

A few pages I came back to while writing this: