Knowledge Concepts
What is a commonplace book? A clear explanation of the centuries-old knowledge collection practice, famous examples, and how to build a modern digital version for writers and researchers.
A commonplace book is a personal collection of quotes, passages, ideas, and observations gathered from reading and experience — organized by theme rather than source — that a person returns to for reference, inspiration, and the development of their own thinking over months and years.
The practice has a 500-year history. Writers, scientists, philosophers, and statesmen from John Locke to Charles Darwin to Ryan Holiday have maintained commonplace books. It is arguably the oldest and most durable personal knowledge management practice in recorded history.
The tradition of commonplace books (from the Latin locus communis — "common place") emerged in Renaissance Europe as literacy spread among educated laypeople. Students were taught to keep notebooks organized by theme — a page for "justice," a page for "friendship," a page for "rhetoric" — where they recorded passages from their reading that related to each theme.
Humanist scholars like Erasmus and Montaigne were practitioners. John Locke developed a formal indexing system for his commonplace book in 1685 — a method so effective that it was published separately as A New Method of Making Common-Place-Books in 1706.
Notable historical commonplace keepers:
The tradition declined in the 20th century as mass printing made reference books widely available — it was less necessary to copy passages from rare texts. But the digital PKM movement has revived interest in the practice, with tools like Obsidian and Notion replacing the notebook.
A commonplace book is not a diary (which records what you did) or a notebook (which captures meeting notes and tasks). It's a curated collection of things worth keeping from sources outside yourself.
Quotes — Passages from books, articles, speeches, conversations that articulate something precisely. The standard: would I want to be able to find and reread this in two years?
Observations — Your own observations about the world that crystallize in language. Not "diary entry" level but "insight worth preserving" level.
Passages — Longer extracts from texts that capture a full argument, scene, or description.
Ideas — Original ideas worth developing — not fully formed, but seeds.
Examples — Specific cases and anecdotes that illustrate broader principles.
Questions — Open questions you're sitting with that don't yet have answers.
What doesn't belong: everything you found interesting but might not actually reread. A commonplace book's value is in its quality, not its volume.
Collection — As you read, mark passages worth collecting (physical: pencil in margin; digital: highlight). After finishing a chapter or article, decide which marked passages actually go into the commonplace book.
Entry — Copy the passage with its source (author, title, page). Add a theme/topic tag.
Organization — By theme, not by source. "Leadership" and "Human nature" and "Creativity" as sections, with passages from many different authors under each theme. This is the commonplace book's distinctive feature: it dismantles the structure of its sources and reorganizes by concept.
Use — When writing, speaking, or thinking about a topic, you go to the relevant section of your commonplace book. The passages collected there accelerate your thinking: they provide vocabulary, evidence, and provocation.
A journalist who writes about business strategy:
Over 3 years: collects passages from 40+ books under themes including "Decision-making under uncertainty," "Organizational failure," "Leadership psychology," "Strategy vs. tactics."
Writing an article: on why large companies miss disruptive threats. She opens her "Organizational failure" section. Finds: a passage from Clayton Christensen on the innovator's dilemma, a quotation from Alfred Sloan on decentralization, an observation from Andy Grove on strategic inflection points, a passage from Barbara Tuchman on how institutions march toward avoidable disaster.
Result: Instead of writing from memory and looking up all these sources while on deadline, she has her collected thinking on organizational failure in one place. The article is richer because it draws on years of reading.
Without the commonplace book: she'd vaguely remember reading something relevant, spend 2 hours trying to find it, and probably omit the most interesting material anyway.
The analog version: a physical notebook divided by theme, handwritten entries.
The digital version: a section of Notion, a folder in Obsidian, a Readwise library — anywhere you can store, tag, and search text.
| Format | Best for | Searchable | Portable |
|---|---|---|---|
| Physical notebook | Writers who think on paper; non-linear browsing | No | Yes (carry it) |
| Notion database | Structured tags + multi-property organization | Yes | Yes (cloud) |
| Obsidian folder | PKM practitioners; linking to other notes | Yes | Local files |
| Readwise | Highlights from books and articles automatically | Yes | Cloud |
| WebSnips | Web research as the primary source | Yes | Cloud |
Readwise has become popular as a digital commonplace book specifically for reading highlights: it automatically collects Kindle highlights, web article highlights, and podcast notes into a searchable library.
| Method | Organizes by | Source preserved? | Links between ideas? |
|---|---|---|---|
| Commonplace book | Theme | Yes (source cited) | No (thematic collocation) |
| Zettelkasten | Idea (atomic) | Yes (lit notes) | Yes (explicit links) |
| Second brain (PARA) | Actionability | Yes | No |
| Evergreen notes | Concept | Partially | Yes |
The commonplace book is the oldest and simplest. It lacks the linking of Zettelkasten and the actionability-sorting of PARA, but its thematic organization is intuitive and has proven effective across centuries.
For writers who draw primarily on quotes and passages from reading (rather than building their own atomic ideas), the commonplace book is often more natural than Zettelkasten.
For writers whose primary reading is on the web, WebSnips functions as a digital commonplace book for web content:
For web-native writers, WebSnips is closer in spirit to a digital commonplace book than tools like Obsidian or Notion, because it focuses on web content as the source material and writing as the output.
Do I need to handwrite my commonplace book? No — the medium is irrelevant. The practice is what matters: curated collection, thematic organization, regular use. Digital is more searchable; analog may slow down capture in a useful way (forcing more selectivity). Neither is inherently superior; use what you'll maintain.
How do I decide what to include? The standard most commonplace book practitioners use: "Would I want to be able to find and reread this in two years, and would it be worth the trouble of recording it?" Most material doesn't pass this test. Selectivity is the point. A commonplace book with 200 truly excellent entries is more valuable than one with 2,000 decent ones.
How is a commonplace book different from just taking notes? Notes are often temporary, contextual, and action-oriented. A commonplace book is permanent, thematic, and reference-oriented. Most note-taking is "things I need to remember for now." A commonplace book is "things I want to be able to access forever."
Who are famous commonplace book keepers I can learn from? Ryan Holiday has written extensively about his physical commonplace book system (he uses index cards, inspired by Robert Greene). Maria Popova's Brain Pickings (now The Marginalian) is essentially a public commonplace book in blog form. Sönke Ahrens's How to Take Smart Notes discusses the commonplace book tradition and its evolution into the Zettelkasten.
A commonplace book is a personal collection of quotes, passages, and ideas organized by theme — one of the oldest and most durable personal knowledge management practices, maintained by some of the most productive thinkers in history.
The practice is simple: collect what's worth keeping, organize by theme, use it when writing. The digital version is more searchable and portable; the analog version may support deeper engagement. Both work.
The commonplace book's enduring value: it turns reading from a passive activity into an input to a knowledge base you actually own.
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A commonplace book is a personal collection of quotes, ideas, passages, and observations gathered from reading and experience — organized for retrieval and creative use. It's the original external memory and idea repository, practiced by writers for centuries.
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