Plexii glossary
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.
The term is most useful as a shared description. It does not remove the need to look at the actual task, evidence or constraint in front of you.
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 (plexii areas); desks keep a task’s notes, files and pages together; Plexii answers from your own work with sources (ai assistant).