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The commonplace book: a complete guide

What is a commonplace book?

A commonplace book is a personal collection of passages, quotes, observations, and ideas gathered from reading and experience, kept in a notebook or equivalent and consulted as a resource for thinking and writing.

The tradition is ancient. The practice emerged from Greek and Roman rhetorical culture, where scholars collected fragments from texts deemed useful, wise, or memorable. The Latin term was loci communes, "commonplaces of knowledge": passages and ideas considered sufficiently important to commit to memory and return to.

The practice evolved through medieval scholarship and became widespread during the Renaissance, when the printing press flooded Europe with more text than any individual could absorb. Educated people developed systematic ways to cope: notebooks filled with extracts, organised by theme, to serve as personal reference libraries. Jonathan Swift captured the spirit of the thing in 1721: a commonplace book is something "a provident poet cannot subsist without, for this proverbial reason, that great wits have short memories."

Darwin kept one. Montaigne kept one. Milton, Locke, Jefferson, Emerson, John Stuart Mill. The practice cut across intellectual traditions because it solved a universal problem: you read things that change how you think, and then you forget them.

John Locke's method

The most systematic account of how to keep a commonplace book came from John Locke, who developed his approach over twenty-five years of personal note-taking and published it in French in 1685, with an English translation appearing posthumously in 1706.

Locke's core contribution was an indexing system. He recommended keeping two pages at the front of the book with an expandable index, a line for each letter of the alphabet and subdivisions for each vowel. When you added a new entry, you noted its page number under the relevant letter and vowel combination. This let you retrieve entries on a given topic without reading through the whole book.

The method was influential because it solved the commonplace book's main practical problem: what use is a large collection if you can't find anything in it? Locke's index provided just enough order to locate things without imposing so much structure that the collection became rigid. Publishers started printing blank commonplace books with pre-made indexes based on his method.

His instructions for what to collect were equally considered. He wrote: "We extract only those things which are Choice and Excellent, either for the matter itself, or else the elegancy of the expression, and not what comes next." The commonplace book wasn't a transcription of everything you read. It was a curated selection of the best of what you encountered.

What goes in a commonplace book

The traditional answer is: whatever strikes you as worth keeping. Quotes that capture something you believe or challenge something you believe. Passages that illuminate a concept more clearly than anything you've read before. Observations from your own experience that seem significant. Fragments of dialogue, poems, descriptions of places, statistics, questions you can't answer.

The practical discipline is selectivity. A commonplace book that contains everything is just a filing cabinet. A commonplace book that contains only the things that actually moved or changed you becomes, over time, a map of your intellectual life: the ideas and moments that shaped how you think.

Some people organise strictly by topic (a section for philosophy, a section for writing, a section for science). Others organise loosely, adding things as they come and trusting the index to make entries findable. Some keep multiple books by theme; others keep everything in one. Locke recommended several specialised books alongside a general one.

The minimum is a heading and the source. Most people also add brief notes on why they extracted the passage: what it means to them, how it connects to something else, what question it raises. These personal annotations are often what makes a commonplace book worth returning to, because they capture the moment of encounter as well as the content.

The practice today

The commonplace book tradition has its most direct modern descendant in the second brain and Zettelkasten approaches, both of which are built on the same foundational intuition: that knowledge worth keeping deserves a dedicated home outside your head, where you can return to it, accumulate it, and let it compound over time.

The differences are in emphasis and scope. A traditional commonplace book collects other people's ideas, quotes, and passages. Zettelkasten emphasises developing your own ideas, written in your own words, with the source material as a substrate rather than the main content. Building a Second Brain focuses on organising all your digital information for eventual creative output. A digital garden takes the commonplace spirit public.

But the underlying logic is the same as Locke's: an external memory that selects and preserves what matters, so your thinking isn't limited by what you can spontaneously recall.

The practice also connects to progressive summarisation: the act of highlighting and annotating a passage, then returning to it later and adding further notes, is a form of commonplacing that develops across multiple passes rather than in a single capture moment.

Physical vs digital

The case for physical: writing by hand forces you to be selective, because you can't write as fast as you can copy and paste. The constraint produces better curation. There's also evidence that handwriting improves retention of what you write. And a physical book doesn't require software, doesn't break, and can survive decades in a way that depends on no company's continued existence.

The case for digital: searchability is transformative. Locke's elaborate indexing system solved a problem that semantic search solves automatically. You describe what you're looking for and it finds the entry, even if you don't remember how you categorised it or what you called it. Digital notebooks can also incorporate images, links, audio, and PDFs alongside text, which a physical book cannot.

Many people use both: a physical notebook for the initial capture (slower, more deliberate, more likely to stick in memory) and a digital tool for longer-term storage and retrieval. The email-to-note and web clipper features of tools like Fabric reduce the friction of digital capture without requiring you to abandon the physical habit entirely.

Starting a commonplace book

You need nothing more than a notebook or a notes app and the habit of writing things down when they strike you.

A few conventions worth establishing:

Always note the source. Author, title, and (for physical books) page number. You'll want to find the original context later, or cite it, or recommend it to someone. Notes without sources become floating fragments disconnected from their context.

Keep your own response alongside the quote. Why did you note this? What does it connect to? What question does it raise? These responses are often the most useful part of the entry when you return to it later.

Review occasionally. The value of a commonplace book compounds through review: returning to old entries in the light of new reading, noticing connections you couldn't have seen when you first wrote the entry. Even a ten-minute browse through old entries periodically is enough to keep the collection alive rather than archived.

Don't worry about completeness. A commonplace book is curated, not comprehensive. Not every good passage needs to be transcribed, and a smaller, denser collection of things that actually matter to you is more useful than an exhaustive archive of everything interesting you've encountered.

The deeper purpose

The commonplace book tradition has persisted for two thousand years because it addresses something permanent about how thinking works. We read widely and forget most of it. What stays is often not what was most important but what happened to resonate with whatever we were preoccupied with that week. The commonplace book is an attempt to preserve more than chance memory allows, to accumulate rather than continuously restart, to build up a personal library of thinking from which new thinking can grow.

Robert Darnton, the historian of books and reading, described how Renaissance scholars "broke texts into fragments and assembled them into new patterns by transcribing them in different sections of their notebooks." That remix logic is the same one underlying Building a Second Brain's express step, Zettelkasten's permanent notes, and the digital garden's networked accumulation. The tool has changed. The practice hasn't.

Frequently asked questions

What's the difference between a commonplace book and a journal?

A journal is primarily introspective and chronological: what happened, what you felt, what you're thinking about. A commonplace book is primarily a curated collection of external material: passages from reading, quotes, observations, ideas worth preserving. The commonplace book looks outward; the journal looks inward. Many people keep both.

Should I copy passages verbatim or paraphrase?

Both have value. Verbatim copying preserves the exact language, which matters when the phrasing is part of the point. Paraphrasing in your own words requires you to understand the idea well enough to express it differently, which aids retention and is the principle behind both note-taking basics and Zettelkasten. Many practitioners copy the passage verbatim and then add a paraphrased note below it.

How often should I review my commonplace book?

There's no prescription. Some people browse regularly; some return to it when starting a new project or when they're looking for a particular idea. The minimum is reviewing it occasionally rather than leaving it permanently unread. The value of a commonplace book increases with use, not with accumulation.

What's the difference between a commonplace book and a second brain?

A traditional commonplace book collects primarily other people's best ideas. Building a Second Brain is a broader system that organises all your digital information (notes, files, bookmarks, voice memos) for eventual creative output. A second brain is more comprehensive and project-oriented; a commonplace book is more focused and curated. The spirit is similar; the scope is different.

Can I use an app as a commonplace book?

Yes. The key features to look for are search (so you can find entries without remembering exactly where you filed them), the ability to note the source, and easy capture from whatever you're reading. Fabric's AI search and annotations let you highlight passages in PDFs and notes and make them searchable by meaning, which is closer to what a well-indexed physical commonplace book provides than most note-taking apps.

Is there a wrong way to keep a commonplace book?

The only real failure mode is not returning to it. A commonplace book you add to but never review is just an archive. Review is what activates the connections between entries, surfaces forgotten ideas, and produces the compounding effect that makes the practice valuable over time.