How to build a second brain from the books you read
A second brain for readers is an external memory that captures, organises and retrieves what you read, so ideas build on each other instead of fading. It works best in three layers: a notes app (Obsidian, Notion, Roam), a library of what you've read (Zotero, Hikara), and a layer that shows how it all connects.
Tiago Forte's book Building a Second Brain popularised the idea. Applying it to reading takes a slightly different shape, because books are long, few and connected in ways notes aren't. This guide sets out the three layers, which tools fit each, and where Hikara fits.
Updated By Hikara Team
The three layers
Layer 1 is your notes: highlights, marginalia and your own ideas, in an app like Obsidian, Notion or Roam. Layer 2 is your library: the books themselves, with ratings and dates, in a reading tracker or reference manager. Layer 3 is the connections between books and ideas. Most readers have the first two; the third is usually missing.
Why a reading list isn't enough
A list is ordered by when you read something, not by what it was about. After a few hundred books, finding the one that made a point you half-remember means scrolling and guessing. A connection layer turns that around: you start from an idea or a theme, and the books come back as the answer.
Layer 1: notes
Highlights, notes in the margin, summaries and your own thinking. Capture lightly (Readwise can send highlights into Obsidian or Notion), keep one idea per note, and link notes to each other. Which app you choose matters much less than using it consistently.
Layer 2: your library
The books, with their details plus your ratings, dates and reviews. Zotero is widely used for academic references; Goodreads and LibraryThing are built for readers; Hikara adds AI analysis. Choose by what you need most: citations, a community, a detailed catalogue, or connections.
Layer 3: connections
Typed, scored relationships between the books in your library. Hikara handles book-to-book connections: echoes, challenges and bridges. Links from an idea in your notes to the book it came from are still best made by hand, in your notes app.
Forte's CODE method, applied to books
Tiago Forte's method has four steps: Capture, Organize, Distill, Express. For readers: capture the passages and reactions that strike you; organize notes by what you'll use them for (his PARA scheme: Projects, Areas, Resources, Archives); distill them with progressive summarization, re-highlighting the best of your highlights; and express what you learned by writing or teaching it.
The steps map onto the layers. Capture and distill happen in your notes; organizing books themselves is your library's job; and the connection layer does part of the organizing for you, by showing which books belong together without you filing them.
How to start
Pick one notes app you'll actually use. Pick one place for your library; if your books are on Goodreads, Hikara can import them in one step. Don't build all three layers at once: start with the one causing you the most friction today.
FAQ
Does Hikara replace Obsidian or Notion?
No. Hikara holds your library and the connections between your books; Obsidian and Notion are general notes tools. They work together: ideas in your notes app, books and how they relate in Hikara.
Do I need all three layers?
No. Plenty of readers do fine with notes and a library. The connection layer pays off if you read across several subjects and often reach for an idea without remembering which book it came from.
Where does Readwise fit?
Between the first two layers. Readwise collects highlights from Kindle, Apple Books and other apps, resurfaces them with spaced repetition, and ties each one to its book. It doesn't show how books relate to each other, which is the gap Hikara fills.
Which notes app should I use?
Whichever you'll keep using. Obsidian is strong on owning your files and linking notes; Notion on structured databases; Roam on outlining. Consistency matters more than features.
Want to put this into practice?
Add your books to Hikara and see the echoes, challenges and bridges between them. The free plan needs no card.
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