Commonplace Book: The 17th-Century Productivity System That Actually Works

A commonplace book is a personal notebook where you collect things you don't want to lose: quotes you liked, ideas that surprised you, references you'll need again, the shape of a thought you don't want to forget. The practice is roughly four hundred years old. It survived because it works.

It also happens to be the closest pre-digital equivalent of how an ADHD brain wants to think — branching, accretive, association-heavy, and absolutely useless if you can't see what's in it. Most digital tools have done a bad job of replacing it. We accidentally did a better job, and this is the article where I admit that.

Yeah, we built a commonplace book¹.

A commonplace book — commonplace meaning "a notable passage worth holding in a common place" — is a centuries-old personal information system. Marcus Aurelius kept one. Locke wrote a whole essay about how to organize one. Virginia Woolf had several. Bill Gates supposedly keeps a digital version. The practice is older than printing².

The structure is loose by design. You collect:

The point is not to be exhaustive. The point is to externalize the parts of your thinking you can't reliably hold in your head, so that future-you can find them, build on them, or stumble into the connection you weren't looking for.

This is the same brief as a Zettelkasten, a digital garden, a second brain, an Obsidian vault, and basically every other "tools for thought" project of the last decade. The commonplace book is just the original.

ADHD brains have a known difficulty with working memory and object permanence. The practical version: things that leave your visual field stop existing in your active awareness. You don't forget them in the long-term storage sense. They just stop being usable.

A commonplace book directly addresses this. It is, by definition, a system for putting your thinking somewhere you can see it later. Every entry is a thought rescued from disappearance. Every cross-reference is a connection that no longer has to live inside your skull, which is good news because your skull was not particularly going to keep it.

The ADHD-adult version of the commonplace book is also the reason you have forty-seven browser tabs open right now. Each tab is a candidate entry. Each one represents something I might want later, kept visible because the alternative — closing it and trusting your memory — is not an alternative. The tabs are a commonplace book that fell over and broke.

The problem isn't the impulse. The impulse is correct. The problem is the format. Tabs are an awful place to keep a commonplace book because tabs hide things by default and the whole point of a commonplace book is that nothing hides.

There is a long graveyard of apps that tried to be your digital commonplace book³. Notion. Roam. Obsidian. Logseq. Evernote (rest in peace). DEVONthink. Tana. Reflect. Each one solves the storage problem and then asks you, the ADHD adult, to do the part your brain is structurally bad at: manually capture, manually tag, manually organize, manually maintain.

This is the entire failure mode. A commonplace book is supposed to reduce the cognitive load of keeping track. If keeping the book itself becomes work, you stop keeping it, and within four months your Inbox folder has 312 untagged notes and a vague sense of guilt. We've all been there. The Notion graveyard is real.

The 17th-century leather notebook had one advantage over modern tools: the act of writing something down was the act of capturing it. There was no separate "and now I will tag it later" step. You wrote the quote, you were done. The book did the rest.

Here is the part I find genuinely funny. I built Horse Browser to fix the tab problem. I did not realize until much later that what I had actually built was a commonplace book that maintains itself.

Trails work like this: every page you visit appears in a sidebar as part of a branching map of where you've been. Click a link, it branches off where you came from. Go deeper, the trail extends. Every page stays visible. Every connection between pages is preserved. Nothing has to be tagged, organized, or filed — the browser draws the structure as you browse.

Now read that paragraph again with the commonplace-book lens:

Horse Browser is a commonplace book that builds itself in the background while you do the thing you were going to do anyway. The 17th-century version required discipline. This one requires nothing⁴.

Try Horse Browser free for two weeks. Card upfront, cancel any time before it bills. If your research workflow doesn't feel materially calmer in the first three days, just don't pay.

The reason commonplace books fell out of fashion in the 20th century is that books were replaced by browsers, and browsers don't keep commonplace books. They keep history, which is a chronological list of URLs sorted by when you visited them. Nobody on earth has ever found a useful idea by scrolling chronologically.

What you actually want — what the commonplace book actually offered — is a structural record. Not "what did I look at on Tuesday" but "what was I thinking when I was researching that thing, and how did one idea lead to another." That structure is the thing your brain can't reliably hold and the thing browsers used to actively destroy.

Trails restore it. Not because Horse Browser is a note-taking app — it isn't, please don't try to use it as one — but because the natural shape of browsing is already commonplace-book-shaped, and we just stopped overwriting it.

A psychotherapist with ADHD who recommends Horse Browser to clients calls this externalizing executive function. The commonplace-book tradition called it externalizing memory. They are roughly the same idea, six hundred years apart.

If you are the kind of person who searched "commonplace book" on Google in 2026, you are probably already trying to externalize your thinking by some method. Notes app, Obsidian, a Moleskine, a stack of index cards, voice memos to yourself, screenshots in a folder named "stuff." All of these are real attempts at the same problem and all of them are working harder than they should be.

The original commonplace book worked because the format was light, the entries were natural-language, and the whole thing lived in one visible place. Trails fit those constraints almost perfectly, and they have one feature the 17th century didn't: they keep themselves.

You don't have to remember to write things down. You don't have to tag them. You don't have to maintain the system. You browse. The book grows. The structure of your thinking is preserved in the literal shape of your browsing, and when you come back to it tomorrow it looks exactly like it did when you left.

That is the entire pitch.

Horse Browser is a browser, not a knowledge-management system. If you want to write essays from your notes, search across thousands of entries, or build a published Zettelkasten, you still want a real notes tool. We do not pretend to compete with Obsidian; we compete with Chrome.

What we do is the part that comes before notes — the messy, branching, tab-hoarding research stage where most people lose the thread before they ever sit down to write. That's where commonplace books did their best work. That's where Trails do theirs.

For most people who think they need a notes app, what they actually need is a browser that stops losing things. Try the simpler fix first.