Leonardo’s notebooks are useful not because they reveal a magical system, but because they preserve thought before it has been separated into neat disciplines.
The page before the category
A Leonardo page can feel less like a finished document than a desk caught mid-thought. A geometric figure leans toward a practical calculation. A machine appears beside a note about water. Elsewhere, a horse’s leg, a costume, or the anatomy of a head enters the same field. The page has not yet decided whether it belongs to art, engineering, anatomy, or errands.
That mixture is the useful part. Modern work tends to force an early choice: put the observation in one folder, the sketch in another, and the task somewhere else. Leonardo’s surviving sheets show what thinking looks like before those boundaries harden. They are not tidy. They are alive with adjacency.
What the notebooks actually contain
The Victoria and Albert Museum dates Leonardo’s notebook practice to at least the mid-1480s, when he was working in Milan. Its five notebooks, now bound as three Forster Codices, range across hydraulics, weights, proportions, mechanisms, anatomy, clothing, and geometry. The V&A describes Codex Forster III as the most miscellaneous of the group: notes on weights and water sit among horse studies, costume drawings, and observations of the human head.
The physical history matters too. The V&A says Leonardo probably worked on loose sheets bought from stationers and carried them so he could record observations. Those sheets were folded into booklets and bound later. The surviving codices are not arranged in a simple logical order. What looks to us like a designed notebook system is partly the result of later handling, binding, and preservation.
Capture before you classify
You do not need to copy Leonardo’s handwriting. The useful habit is to capture thoughts first, keep related ideas together while they form, and connect them later. A question can remain beside a sketch. A practical task can stay close to the idea that produced it. The page becomes a temporary meeting place rather than a filing cabinet.
That matters because categorizing is a different mental act from noticing. The moment you ask where an idea belongs, you add a decision. Sometimes that decision is useful. Sometimes it is enough friction for a small observation to disappear. Capture can be permissive; organization can happen when there is actually something worth organizing.
Resist the genius myth
Leonardo’s mirror writing is a good warning against overconfident stories. The V&A notes several possible explanations, including his left-handedness and the fact that mirror writing was known to writing masters of the period. It does not reduce the practice to a secret code. Where the evidence is uncertain, the honest move is to keep it uncertain.
The same restraint applies to the notebooks as a whole. They are not proof that mixed pages create genius. They are evidence that one extraordinarily observant person used drawing and writing together as instruments of inquiry. The repeatable idea is smaller and more democratic: do not make a thought prove its category before it earns a place on the page.
Try one deliberately mixed page
For one day, keep a page open to five kinds of trace: one question, one observation, one sketch, one task, and one idea. Do not build sections in advance. Add each item where the next empty space invites it. The aim is not chaos for its own sake; it is to preserve the context in which different kinds of thought arrived together.
At the end of the day, look for one useful adjacency. Perhaps the task explains the worry. Perhaps the sketch changes the question. Perhaps the observation gives the idea a setting. Only then decide what should be moved, developed, or scheduled. The page has done its work when it helps you notice something that a set of perfect folders would have kept apart.