Glossary
Second brain
Definition: a trusted external memory system — usually a notes app or knowledge base — that you offload remembering to, so your conscious attention is free for thinking.
Plain-English definition
A "second brain" is a personal knowledge tool you trust enough to outsource memory to. The first brain (yours) handles thinking and judgment. The second brain (your system) handles capture, recall, and the slow accretion of context over years.
Origin
The phrase was popularized by Tiago Forte in the "Building a Second Brain" (BASB) methodology, an extension of older personal knowledge management practices. It overlaps with but is not identical to PKM.
Modern implementations
- Markdown vaults (Obsidian, Logseq, MindWiki) — files on disk, wikilinks, properties.
- Outliner systems (Roam Research, Tana, Logseq) — bullets/blocks as the atomic unit.
- Object-first systems (Capacities) — typed objects per concept.
- AI-connected vaults (MindWiki) — MCP/REST surface so AI clients read and write alongside you.