Thomas Jefferson kept one. So did John Milton, Francis Bacon, and generations of students at Oxford. It was among the most widely taught study habits in the Western world for centuries, and today almost no one has heard of it. The commonplace book is a simple notebook with a simple purpose: to capture the best things you read, so they become part of you instead of slipping away.

If you want your son to become a thoughtful reader, or you want to become one yourself, this is the habit to build. Here is how to keep a commonplace book.

What it is

A commonplace book is a personal notebook of passages, quotations, facts, and ideas, copied by hand from what you read and organized by subject rather than by date. According to its history, the name comes from the Latin locus communis, a “common place,” a term the ancient rhetoricians used for the standard topics and arguments a speaker could draw on. Aristotle, Cicero, and Quintilian all discussed commonplaces as tools for thinking and speaking.

The notebook turned those topics into a physical collection. A reader would keep headings such as Courage, Friendship, Death, Government, or Education, and under each he would copy the best lines he found on the subject.

Who kept one

The list is impressive. Jefferson kept separate commonplace books for literature and law. Milton kept notes with citations that fed his writing. Bacon kept a collection of phrases and turns of speech. In 1706, John Locke’s A New Method of Making Common-Place-Books was published in English, laying out a system for organizing entries by subject that many readers adopted. By the seventeenth century, commonplacing was taught formally at Oxford, and it remained a standard study technique into the early twentieth century.

In other words, this is not a hobby. It is how serious readers read.

How to start

Get a real notebook. A sturdy, bound notebook with numbered pages works best. It should feel worth keeping for decades.

Leave the first pages for an index. As you add headings, list them at the front with page numbers, so you can find everything later. This is the essence of Locke’s method.

Copy by hand. This is the part people want to skip, and it is the part that matters most. Copying a passage slowly forces you to read it closely, and it lodges the words in memory in a way that highlighting never does.

Always record the source. Author, title, and page. A quotation without a source is useless when you want to cite it later, and the habit of attribution is itself a form of honesty.

Add a line of your own. After a passage, write a sentence about why it struck you, or where you disagree. Over years, those notes become a record of how your mind has grown.

What to copy

Anything worth remembering, but a few categories are especially useful for a young man:

• Lines of courage and duty from biographies and histories, especially Plutarch.
• Clear definitions of important ideas, such as justice, liberty, or virtue.
• Well made sentences you would like to be able to write yourself.
• Arguments on both sides of questions you care about.
• Scripture and poetry you want to carry with you. Our list of poems every boy should memorize is a good start.

How to teach it to a boy

Start with a single heading. Give him a notebook and tell him that every time he reads something about courage, he should copy it under that heading. After a month, sit down together and read through what he has collected. Then add a second heading.

By sixteen, a boy who has kept the habit will have a personal anthology of hundreds of passages he chose himself. When he has to write an essay or give a speech, he will not stare at a blank page. He will open his notebook, which is exactly what the ancients intended. It is the natural companion to learning rhetoric, where the commonplaces began.

Why it works

Reading without writing is like eating without digesting. We forget most of what we read within days. The commonplace book slows reading down, forces judgment about what matters, and builds a store of wisdom that is truly one’s own.

The men of the Gentlemen’s Classics Book Club read Plutarch’s Lives week by week, and a commonplace book is the ideal companion to that kind of reading. For more on how to read a great book well, see our guide to reading Plutarch and our essay on why the smartest men are still reading books written by ghosts.