# Second brain

> An external system for capturing notes, sources and ideas so they can be found and used later.

## What it means

What people mean by it: a trusted, external system for notes, references and ideas, so your head is free for thinking; popularised by Tiago Forte’s book Building a Second Brain (2022) — Distinguish it from personal knowledge management, a knowledge base and a zettelkasten in one line each. The newer ‘second brain AI’ searches (rising in autocomplete): an assistant that answers from your own notes.

## A practical example

A meeting note links to the client, project, decision and next action, so the idea can be found from any of those paths later.

## Put it into practice

- Name the concrete situation before applying the label. Second brain is useful only when it changes a choice, boundary or next action.
- Make the state visible: write the owner, time, source or stopping condition down instead of relying on memory.
- Review what happened. Keep the part that reduced ambiguity and change the part that added ceremony without helping the work.

## How it relates to Plexii

the Brain area holds Ask Brain (your knowledge base), Search and Brain Map (/help/plexii-areas); desks keep a task’s notes, files and pages together; Plexii answers from your own work with sources (/help/ai-assistant).