The Commonplace Book: A 2,000-Year-Old Thinking Tool

A commonplace book is a personal notebook for collecting quotes, ideas, and observations — anything worth remembering. For over two thousand years, it has been the quiet engine behind an extraordinary amount of the world's best thinking. And there's a good chance you've already been keeping one without knowing its name.

Marcus Aurelius kept one in a military tent on the Danube frontier. Leonardo da Vinci kept one full of sketches, grocery lists, and engineering ideas all jumbled together. Montaigne kept one and accidentally turned it into one of the greatest books ever written. Darwin kept one and used it to sketch the first diagram of evolutionary theory, scribbling "I think" in the margin above a spindly tree of life.

Every time you save a quote in your phone, highlight a passage you mean to come back to, or jot down something you heard — you're commonplacing. The practice is ancient. The instinct is universal.

What is a commonplace book?

A commonplace book is a personal notebook for collecting anything you find interesting, useful, or worth remembering — quotes, ideas, observations, passages from books, overheard conversations, recipes, poems, anything. Unlike a diary, it isn't organized by date and isn't about recording what happened to you. It's about curating what you think.

The practice of keeping one — sometimes called a commonplace journal or commonplace notebook — is called commonplacing, and it's been around since ancient Greece. What goes in a commonplace book? Whatever you want. Historically, people have filled theirs with quotes, proverbs, recipes, poems, sketches, half-formed arguments, questions, and things they overheard on the street. The range is the point. A commonplace book isn't a filing system. It's a personal record of your intellectual life — messy, eclectic, and entirely yours. No two look the same, because no two minds work the same way.

The tradition: from Marcus Aurelius to Bruce Lee

The most famous commonplace book examples span two millennia — from Marcus Aurelius's private reflections in a Roman military camp to Bruce Lee's philosophical notebooks in 1970s Los Angeles. What connects them is a shared conviction: that thinking happens on the page, not just in the head. The external surface isn't a convenience. It's where the work gets done.

Thinking happens on the page, not in the head

Of all the famous commonplace books in history, the most famous was never meant to be read by anyone. Marcus Aurelius composed his Meditations as a private collection of quotes, reflections, and reminders to himself. The philosopher Pierre Hadot, who spent decades studying the work, described it as personal notes that Marcus wrote in his own hand, day by day, with no intention of publication. It is a commonplace book that accidentally became one of the most influential philosophical texts in history.

He wasn't the only ancient practitioner. A century earlier, Seneca described his own method of collecting passages each evening. "We should follow the example of the bees," he wrote, "who flit about and cull the flowers." Read widely, claim some part for yourself, work it over until it becomes your own. The ancients understood something modern productivity culture keeps rediscovering: thinking happens on the page, not just in the head.

The first information explosion

In the 1440s, the printing press created something the world had never seen: more books than any person could read in a lifetime. For the first time, the problem wasn't access to information. It was deciding what to keep.

The response was a commonplace book boom. Erasmus published De Copia in 1512 — essentially an instruction manual for commonplacing. He advised students to read with a notebook open, excerpt useful passages, and arrange them under topical headings. The book went through over a hundred editions and became the standard textbook across northern Europe. For two centuries, keeping a commonplace book wasn't a quirky habit. It was the foundation of a good education.

Leonardo da Vinci needed no instruction. His codices are the ultimate commonplace books — engineering sketches next to anatomical drawings next to grocery lists (one famous list includes "spectacles with case, human skull, nutmeg") next to observations about water. No categories, no system. Just everything he found interesting, committed to paper.

Montaigne's Essais — the book that invented the essay as a literary form — grew directly from his commonplace practice of collecting and annotating passages. He had fifty-seven maxims painted on the ceiling beams of his library tower. His earliest essays were little more than compilations of collected thoughts. The published masterpiece emerged from a lifetime of writing things down.

The Italians had their own word for this kind of notebook: the zibaldone — a "salad of many herbs." The printing press created the first great information explosion, and the commonplace book was the response: when there's more to read than any person can absorb, you develop a practice for deciding what to keep. Sound familiar?

The notebook as creative engine

In 1685, John Locke — the philosopher whose ideas about natural rights shaped the American and French Revolutions — described how he organized his personal notebook. His system was elegant: an alphabetical index at the back, entries organized by the first letter of a word and the first vowel that followed. Just enough structure to find things later, without dictating what you should collect. Publishers sold blank notebooks based on his method for over a century.

Isaac Newton's famous Waste Book — originally a theological commonplace book belonging to his stepfather — became the surface where he worked out his early calculus beginning in 1664. One of the most transformative intellectual breakthroughs in history, worked out in someone else's old notebook.

Charles Darwin opened Notebook B in July 1837, and on page 36, drew a branching diagram with the words "I think" written above it. It was the first sketch of what would become the theory of evolution. The theory didn't arrive as a flash of insight. It was worked out slowly, in notebooks filled with observations, questions, and half-formed ideas converging on a page.

Virginia Woolf kept her reading notebooks separate from her diary. This matters: her thirty volumes of diary recorded her life. Her sixty-seven reading notebooks — roughly 7,000 manuscript pages — recorded her intellectual encounters. The commonplace book was her thinking space. The diary was her living space. She understood they did different things.

Beethoven carried pocket-sized sketchbooks outdoors and used larger desk sketchbooks at home. Symphonic ideas lived alongside mundane daily notes. Emerson called his journals his "Savings Bank" — raw material he could draw on for lectures and essays. The pattern is clear: the most original creators didn't separate note-taking from creative work. The notebook was where creation happened. The published work was just the part that made it out.

The age that built modern science and democracy ran on commonplace books. These were not dilettantes. They were people who changed the world, and this was their thinking infrastructure.

A universal practice

This is not a European invention. Every literate civilization independently developed its own version.

In Japan, the zuihitsu ("following one's brush") produced Sei Shōnagon's The Pillow Book around 1002 CE — intimate observations from the Heian court. In China, the biji ("brush notes") tradition produced polymath works like Shen Kuo's thirty-volume Dream Pool Essays around 1088. In Korea, the p'ilgi tradition produced literary miscellanies. In the Islamic world, the kashkul (literally "beggar's bowl") was a notebook filled gradually with whatever one encountered. In India, the subhāṣita tradition compiled thousands of epigrammatic wisdom verses. In Timbuktu, an estimated 300,000 manuscripts survive, some dating to the thirteenth century.

That convergence — independent invention across every major civilization — is the strongest evidence that the commonplace book answers a fundamental human need. When people learn to read and write, they start collecting what matters to them. The format varies. The impulse doesn't.

The twentieth century didn't abandon the commonplace book. It just stopped using the name. Bruce Lee — not a scholar, but a martial artist and actor — filled notebooks with philosophy, technique, poetry, and self-reflection, later published as a seven-volume library. Octavia Butler, the science fiction author, wrote in a 1988 notebook: "I shall be a bestselling writer." Her notebooks combined these affirmations with character notes and world-building maps — she used her commonplace book not just to think but to will her future into existence. It worked.

What writing things down does to your brain

The greatest thinkers in history intuited that writing things down changed how they thought. Modern science explains why. Decades of research converge on a consistent finding: selecting an idea, writing it down in your own words, and revisiting it later fundamentally changes how your brain processes information. A commonplace book, it turns out, is built on solid cognitive science.

Memory and deeper processing

The most relevant finding is the generation effect: producing information in your own words creates stronger memory traces than passively reading or highlighting. The original study (Slamecka and Graf, 1978) has been replicated extensively — a meta-analysis across eighty-six studies found a consistent, moderate effect. It's one of the most robust findings in memory research. And it maps directly onto what a commonplace book demands: you don't just consume. You select, rephrase, and write.

This connects to Craik and Lockhart's levels of processing framework: the deeper you engage with information — connecting it to what you already know, rephrasing it — the more durably you remember it. Placing a new idea into the context of your existing commonplace book is exactly this kind of deep processing.

Then there's spaced repetition — revisiting material at increasing intervals, widely considered one of the most effective learning techniques known. Flipping through a commonplace book — browsing half-forgotten entries alongside recent ones — is an informal version of exactly this.

Emotional clarity

James Pennebaker's expressive writing research, beginning in the 1980s, found that writing about experiences and emotions could improve mood, immune function, and psychological well-being. Over a hundred studies have explored this, with mixed but suggestive results. One finding has held up consistently: unstructured writing works. You don't need a template. You need a practice of putting thoughts on a page.

The neuroscience of affect labeling is on firmer ground. Brain imaging studies show that the simple act of naming an emotion in words diminishes the amygdala's response while activating regulatory regions of the prefrontal cortex. Writing about how something makes you feel literally changes how your brain processes that feeling. A commonplace book that includes your reflections alongside collected material — not just what struck you, but why — naturally facilitates this.

This is, in essence, what Marcus Aurelius was doing in his tent on the Danube. Writing to himself to regulate himself. The practice is two thousand years older than the neuroscience that explains it.

Creativity and unexpected connections

Here's where the commonplace book becomes something more than a memory tool.

Research on creativity consistently finds that new ideas emerge from combining existing ideas across unrelated domains. Arthur Koestler called it bisociation — perceiving a situation in two incompatible frames of reference simultaneously. Creativity isn't conjuring something from nothing. It's collision.

A commonplace book is, by design, a collision engine. You put Seneca next to a recipe next to an observation about your daughter next to a passage from a neuroscience paper. Over time, connections emerge that would never happen in a neatly organized system.

The philosophers Andy Clark and David Chalmers argued in their famous 1998 paper "The Extended Mind" that when external tools reliably supplement cognitive processes, they become part of the cognitive system itself. Their thought experiment: a man named Otto uses a notebook to supplement his failing memory. Clark and Chalmers argued Otto's notebook is, functionally, part of his mind. A commonplace book is perhaps the most direct real-world version of this idea. It's not a backup of your brain. It's an extension of it.

One thread runs through all this research: the science supports unstructured capture over rigid systems. The generation effect requires engagement, not organization. Combinatorial creativity requires disorder. Pennebaker found freewriting works. The science is on the side of the person who writes things down because they're interesting, not the person who agonizes over which folder to file them in.

Journals record your life. Commonplace books record your thinking.

The difference between a commonplace book and a journal is the source. A journal records what happened to you, organized by date. A commonplace book curates what you think, organized by interest. One captures your experience. The other captures the passage that stopped you mid-sentence, the connection between two ideas, the quote you want to carry.

Virginia Woolf kept both because she understood they did different things.

A bullet journal is a productivity system. It tracks tasks, habits, and goals. There's nothing wrong with it, but a commonplace book has no goals, nothing to track, nothing to optimize. You're not trying to get more done. You're trying to think more clearly.

A "second brain" (Tiago Forte's PARA method, Zettelkasten) is optimized for retrieval — filing things so you can find them later. A commonplace book is optimized for encounter — collecting things so they bump into each other and produce new thinking. The value isn't in perfect retrieval. It's in the surprise of finding something you'd half-forgotten next to something you captured yesterday.

The lack of structure isn't a bug. It's the entire point. Leonardo didn't have a tagging system. Montaigne didn't do weekly reviews. They just wrote down what struck them.

Starting your first commonplace book

Starting and keeping a commonplace book is simple. You need something to write in and a willingness to capture what interests you. The categories, the organization, the perfect system — all of that emerges from keeping the practice, not from planning one. Don't plan it. Just begin.

Choose your medium

A physical notebook works if you want a break from screens or you're a tactile thinker. Index cards have a devoted following — Ryan Holiday maintains over 10,000 handwritten 4×6 cards and explicitly traces the method to the commonplace book tradition. Cards can be rearranged and grouped in ways a bound notebook can't.

Digital tools are the modern commonplace book in practice. Apps like Leo, Notion, and Obsidian each handle digital commonplacing differently — we compared the field in our guide to the best Obsidian alternatives. They work well if you consume most of your information on a screen.

The only wrong choice is the one that creates enough friction to stop you from writing things down.

Ideas for your commonplace book

If you're looking for commonplace book ideas — or commonplace journal ideas — the answer is the same one practitioners have given for centuries: anything that earned a second look. The categories below are where most entries land.

Quotes and passages — the lines that made you stop and think. Not comprehensive notes, just the parts that earned a second look.

Your own observations and questions. Half-formed ideas count. Darwin's "I think" sketch wasn't a finished theory. It was a question in a notebook.

Connections between things. Something about economics that reminds you of ecology. Write that down. This is where the combinatorial magic happens.

Things you want to remember. Facts, recipes, words in other languages, instructions. If it's worth remembering, it's worth writing down.

Your responses. Not just the source material but your reaction. Why did it matter? What do you disagree with? The most valuable entries are often where you talked back to what you read.

A commonplace book template (Locke's method)

Most of the greatest commonplace books in history weren't organized at all. Marcus Aurelius wrote chronologically. Leonardo wrote wherever there was space.

If you want a commonplace book template — some structure to start from — Locke's index method is the closest thing to a standard format the tradition has. A simple alphabetical index at the back, recording topic and page number for each entry, has worked for over three centuries. Thematic grouping into broad categories (quotes, ideas, observations) keeps things loose without being chaotic. Tagging in digital tools lets an entry live in multiple contexts without forcing you to decide where it "belongs."

Or just keep writing, in order, without a system. The real value of a commonplace book isn't in finding a specific entry. It's in the slow accumulation and the unexpected encounters when you flip through it.

The right system is the one that doesn't get in the way of writing things down.

A first exercise

Pick a book you've recently read. Write out the five passages that stuck with you most. Under each one, write a sentence about why it stuck — what it reminded you of, what you disagreed with, what question it raised.

Congratulations. You've started a commonplace book.

Frequently asked questions

What is a commonplace book?

A commonplace book is a personal notebook where you collect quotes, ideas, observations, and anything else worth remembering. Unlike a journal, it's organized by interest rather than by date. The practice — called commonplacing — dates back over two thousand years and developed independently across virtually every literate civilization.

What is the difference between a commonplace book and a journal?

A journal records your daily experiences chronologically — what happened, who you saw, how the day felt. A commonplace book collects ideas, quotes, and observations from everything you read, hear, and encounter. A journal is about your life. A commonplace book is about your thinking. Virginia Woolf famously kept both, in separate notebooks.

What is the difference between a commonplace book and a bullet journal?

A bullet journal is a productivity system for tracking tasks, habits, and goals using a structured set of symbols and spreads. A commonplace book has no system and no goals — it's a personal collection of whatever interests you. A bullet journal helps you get things done. A commonplace book helps you think more clearly.

What should I put in a commonplace book?

Anything that strikes you: quotes from books, podcast insights, your own observations, recipes, half-formed ideas, questions, connections between things you've learned, even sketches and overheard conversations. The only rule is that it matters to you. Leonardo's notebooks famously included grocery lists alongside anatomical drawings and engineering sketches.

How did John Locke organize his commonplace book?

Locke used a simple alphabetical index at the back of his notebook, recording topic and page number for each entry. The index organized entries by the first letter of a word and the first vowel that followed — enough structure to find things later without dictating how you think.

What are some good commonplace book categories?

Common categories include quotes and passages, personal observations, questions and half-formed ideas, reading notes, connections between different subjects, and practical information like recipes or instructions. But most practitioners keep it loose — broad neighborhoods, not strict filing systems.

Is there a commonplace book app?

Yes. Leo, Notion, and Obsidian each support digital commonplacing in different ways. Leo is a native Mac app designed for capturing ideas alongside video and audio content. Notion offers databases and templates. Obsidian provides local markdown files with linking. See our comparison of Obsidian alternatives for a detailed head-to-head of all three.

Who are some famous people who kept commonplace books?

Marcus Aurelius, Leonardo da Vinci, Montaigne, John Locke, Isaac Newton, Charles Darwin, Virginia Woolf, Beethoven, Bruce Lee, and Octavia Butler all kept commonplace books or equivalent notebooks. The practice spans philosophy, science, literature, music, martial arts, and more.