Main idea

A book summary stays a prisoner of its book. It keeps what the book said, in the order it said it, and what you retain six months later is a vague recollection — "that author said something about that subject" — which forces you to reopen the source to recover the idea. Knowledge is then filed by origin, and every new reading produces one more summary sitting beside the previous ones.

Filing by concept flips the axis. The unit is no longer the book but the idea, and a single idea can take in what three books, two conversations and one project have brought to it. The note stops being "the note from chapter 3" and becomes an available building block.

The gain is therefore not one of tidiness but of accumulation: two readings on the same subject settle in the same place instead of living in two summaries that ignore each other.

Why it matters

This explains why some knowledge bases grow denser while others merely grow bigger. A base filed by origin expands linearly with the sources read, without any of its entries becoming any more solid; a base filed by concept gets better at what it already holds.

It also changes what you do with a new source. The question is no longer "where do I file this reading?" but "what does it confirm, qualify or limit in what I already think?".

Nuances and limits

The source axis keeps a function. Traceability, exact quotation, going back to the original all assume you know which text a given thing came from — origin does not disappear, it merely stops being the filing principle.

Layer added by "Graphify without AI: turning a wiki into a navigable graph for zero tokens" (2026-10-20). The source axis can come back through navigation. In a wiki filed by concept, each book keeps a reading map that points to the notes it has fed; those reading maps are the most connected nodes in the knowledge base, and an automatic grouping splits a concept such as positioning across five groups, mostly by source book. Filing by concept holds in the notes, not necessarily in the graph they form.

Layer added by "Start from scratch or copy: two ways to lose what you know" (2026-10-30). The same reversal applies to security questionnaires sent by prospects. Filed by client file, a question numbered "14.6.l" by one and "CL-072" by another stay strangers; filed by topic, they come together on backups. The question asked of the knowledge base changes with the axis: no longer "what did we answer to that client?" but "what do we know how to answer on this topic?".

And the shift carries a cost paid on every reading: recognising that an idea is already there assumes you know your own knowledge base, which a book summary never demands.

Open questions

• How do you recognise that a new source brings a nuance to an existing note rather than a distinct idea, without rereading the whole knowledge base?