Keeping a slip-box: one idea to a card

Most of us already keep notes. They live in the backs of notebooks, in a file called “ideas” that nobody opens, in highlights we will never look at again. A slip-box is a different habit, and a modest one: you write each idea on its own small card, in your own words, and you file it next to the ideas it belongs with. Over months the cards begin to talk to each other. That is the whole promise, and it is enough.

The room you are standing in takes its name from this habit, so it seems right that the first slip on our own shelf should be about it. What follows is the way we would suggest starting, not a system to obey. Change any part of it that does not suit the way you think.

One idea to a slip

The rule that does most of the work is also the simplest: one idea per card. Not one book, not one lecture, not one afternoon of reading. One thought you could state in a sentence or two.

This feels wasteful at first. It is tempting to fill a card with everything a chapter said. Resist it. A crowded card can only be filed in one place, and so it can only ever be found from one direction. A card that holds a single idea can sit beside other single ideas, and that is where the interesting connections come from: a remark about attention in a book on painting, filed next to a note on how long people can listen to a sermon, filed next to your own suspicion that short paragraphs make readers impatient.

A useful test: if you cannot give the card a short title that covers everything on it, it is probably two cards.

What goes on a card

Every card we keep has the same four parts, in the same places, so the eye knows where to look.

• A title at the top, written as a claim rather than a topic. “Readers forgive difficulty, not confusion” is a title. “Readability” is a drawer label.
• The idea itself, in your own words. This is the part that matters most. Copying a sentence out of a book feels like work, but it is mostly transcription. Restating it forces you to decide what you think it means, and that decision is what you will need later when you write.
• A source line: author, title, page, or the conversation it came from. If the idea is yours, say so. Future you will want to know which thoughts were borrowed.
• Links to other cards, by number, with a word or two on why. “See 14b: same point, but about music.”

Short quotations are fine when the exact wording is the point, but mark them clearly as quotations and keep them short. A slip-box full of other people’s sentences is a commonplace book, which is a fine thing to keep, but it is a different tool.

Numbers and neighbours, not folders

The habit that makes a slip-box feel alive is filing a new card next to the card it most belongs with, rather than in a folder by subject. The usual way to do this on paper is a branching number.

Your first card is 1. A card that follows from it in a new direction is 2. A card that continues or comments on card 1 is 1a; a card that comments on 1a is 1a1; a second comment on card 1 is 1b. You never renumber. A new idea simply slots in after its nearest relative, and a line of thought can grow sideways for as long as it needs to.

This sounds fussy, and for the first few weeks it is. The payoff comes later, when you pull out one card and find, right behind it, a run of related thoughts you had forgotten you had. Folders hide that. A folder called “Reading” tells you where a card is, but not what it is next to.

The best-known example of the method is the card index kept by the German sociologist Niklas Luhmann; the Wikipedia article on the Zettelkasten is a reasonable place to read about its history. You do not need to copy his scheme. You only need some way of saying “this card lives beside that one”.

An index of ways in

A slip-box with no index is a pile. Keep a small set of entry cards, one per subject you return to often, each listing a handful of card numbers where a line of thought begins. You do not need to list every card on a subject, only the doors.

The index should stay short. If an entry grows past a dozen numbers, that is a sign the subject has become two subjects, or that you are ready to write about it. Both are good news.

Tending the box

A slip-box needs a little regular care, the way a garden does. The rhythm we suggest is light:

1. Capture freely. During the week, scribble in the margins of what you read and jot rough notes wherever you are. These are not cards yet.
2. Write cards once a week. Sit down with the week’s scribbles and turn the ones that still interest you into proper cards, in your own words. Throw the rest away without guilt.
3. File each card by hand. Find its nearest neighbour, give it a number, and add at least one link. Filing is where you think; do not rush it.
4. Wander for ten minutes. Pull a card at random and follow its links. Sometimes nothing happens. Sometimes you find the beginning of an essay.

When a run of cards starts to look like an argument, it is time to take them out of the box. We have written separately about that step in From a drawer of notes to a finished essay.

Paper or screen

People argue about this more than it deserves. Paper cards are slow, which is their virtue: you cannot paste, so you have to restate. They are also pleasant to lay out on a table when you are building a piece. Digital notes are searchable and travel with you, and linking is a click. Either works if you keep the two rules that matter: one idea per note, and every note filed beside a neighbour with a reason written down.

Whatever you choose, give it a season before you judge it. The value of a slip-box is cumulative, and it is hard to see in the first month. If you write on a shelf here, it can be worth publishing the occasional working note as you go, filed in a drawer of its own, so readers can watch a line of thought take shape. The features page describes how drawers and subject headings work on a writer’s shelf.