Commonplace book: what it is and how to keep one

A commonplace book is a notebook, or a set of notes on your phone or computer, where you copy passages, quotes, facts and ideas from what you read, sorted by topic so you can find them again. You might copy a line from a novel under "Writing", a number from a news article under "Health" and a tip from a podcast under "Work". A diary records what happened to you. A commonplace book records what you found in other people's words, with a note on why it mattered to you.

The name comes from the Latin locus communis, "a general or common place". Each heading in the book was a place where you kept everything you found on one subject.

Setting one up takes a few minutes, and this post shows three ways to do it. It also covers the step that setup guides usually skip: remembering what you copied, which is what commonplace books were for in the first place.

What goes in a commonplace book

Anything you read or hear that you might want again:

• passages and quotes, copied word for word
• facts and numbers, with where they came from
• ideas you want to try, and questions you want to answer
• your own reactions, like where you disagree with the author

Each entry gets the text, the source (the book and page, or the web address) and a heading for its topic. Add one line in your own words about why you saved it, because a passage that felt important in March can look random in June.

Here's one entry followed through. You're reading Walden and copy Thoreau's line "Our life is frittered away by detail." You write it under the heading Simplicity, add the page number, and note "the weekly status meeting". Two months later you're writing to your team about cutting meetings. You open Simplicity, and the line and your reason for saving it are both there.

A short history of commonplace books

People kept commonplace books most widely during the Renaissance and again in the nineteenth century. By the seventeenth century, students at Oxford were taught how to keep one, and Ralph Waldo Emerson and Henry David Thoreau learned the habit at Harvard.

In 1685 the philosopher John Locke wrote a treatise in French on how he indexed his commonplace books. It came out in English in 1706 as A New Method of Making Common-Place-Books, and a simpler version of his index is still what paper guides teach today.

A few commonplace books that survive:

• Francis Bacon kept a list of useful phrases, the Promus of Formularies and Elegancies, which he probably used to prepare speeches.
• Thomas Jefferson's literary and legal commonplace books have both been published by Princeton University Press.
• Isaac Newton worked out calculus in a commonplace book he called his "waste book".
• Ronald Reagan kept his on index cards, which were published in 2011 as The Notes.

Long before any of them, the Roman teacher Quintilian asked his readers to commit their commonplaces to memory. Copying a passage was the first step, and learning it was the point.

How to start a commonplace book

Pick the format you'll actually open. Here are three that work.

A notebook with an index

This is Locke's method, simplified.

1. Leave the first few pages blank for the index, and number the rest of the pages.
2. Divide the index pages by letter of the alphabet. Give common letters like S and T more room.
3. When you add an entry, write its heading in the margin, like "Simplicity".
4. In the index, write the heading under its first letter, followed by the page number. When you add to the same heading later, add the new page number to the same line.

The notebook can be any size. A plain lined one works, and you don't need to plan the headings in advance.

Index cards

Ryan Holiday keeps his commonplace book on 4x6 index cards, a system he learned from the author Robert Greene. Each card holds one passage or idea, with its topic written in the top corner, and the cards are filed by topic in a box. When he works on something, he pulls out the cards for that topic. A card can move to a new topic whenever it fits better there.

Holiday also waits about a week after finishing a book before he copies anything onto cards. The passages that still look worth keeping after a week go in, and the rest stay in the book.

A notes app

A digital commonplace book can be a folder in Apple Notes, Notion, Obsidian or any app with search. Make one note per entry, give it a tag or a folder for the topic, and paste the link to the source. Search does the job of Locke's index.

The catch is that copying is too easy. You can paste a whole page without deciding what mattered, and a commonplace book full of whole pages is hard to use. Retyping a line, or writing it by hand, makes you pick the part worth keeping. Holiday makes the same case for writing by hand.

If you read on a Kindle, you already have the start of one: the Kindle saves every highlight and note in a file called My Clippings.txt. The free Kindle highlights viewer sorts that file by book and exports it as Markdown for Notion or Obsidian.

How to remember what's in your commonplace book

Copying a passage helps you notice it, but the memory fades like any other. The forgetting curve shows how quickly that happens. Research on memory points to two habits that slow it down: testing yourself, and spacing the tests out.

In a 2006 study by Henry Roediger and Jeffrey Karpicke, students read a short passage. The ones who read it once and then wrote down what they could remember, three times, recalled 61% of it a week later. The ones who kept rereading it recalled 40%. In 2013 a review led by John Dunlosky gave its top rating to two of ten study techniques, practice testing and spreading practice out over time, and rated rereading and highlighting low.

Here's how to use that with a commonplace book:

1. Write a question next to each entry. Next to the Walden line, you could write "What did Thoreau say our life is frittered away by?"
2. Once a week, open a few pages or pull a few cards. Cover the passage, read the question, and answer it before you look.
3. Space the reviews out. An entry you remembered can wait longer before you see it again, and one you forgot should come back soon. Flashcard apps like Anki do this scheduling for you, and the FSRS simulator shows how Anki's newer scheduler picks the dates.
4. Use the entries. Put a passage in an email, an essay or a conversation, which is a test of its own.

There's more on both habits in active recall and spaced repetition.

A commonplace book for the articles you read

I made Bundle to do this for articles. You save an article from your iPhone, from Chrome or on a Boox tablet, read it in a clean reader and highlight the passages you want to keep. Bundle files each article under a topic. When you finish, a Quick check asks you a few questions about the article, and you keep the good ones as cards. Bundle brings each card back with FSRS, the same scheduler as in the simulator, so the review step happens without you writing the questions.

QUICK CHECK · SCIENCE Which night of sleep matters most after you study? The night after. It is at least as important as the night before, because that sleep cements what you learned. Sleep On It: How Snoozing Strengthens MemoriesShow in article

SkipKeep card

Bundle is on the App Store for iPhone, and you can try it free for 14 days.

Questions about commonplace books

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

A journal records your days and your thoughts. A commonplace book collects material from outside sources, like books, articles and talks, sorted by topic so you can find it again. Plenty of people mix the two and write their own reflections next to the passages they copy.

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

A Zettelkasten is the slip box system the sociologist Niklas Luhmann used: short notes in your own words, each numbered and linked to related notes. A commonplace book is sorted by topic and holds more copied passages. You can start with a commonplace book and add links between entries later.

Can a commonplace book be digital?

Yes. Any app with search and tags or folders can do the work of the index. Keep one entry per note, so you can find, move and review entries one at a time.

How long should an entry be?

As short as it can be and still make sense to you in a year. That's usually a sentence or a short paragraph, plus the source and your one-line reason.