Second brain

A second brain with AI, without twelve apps

A second brain is one trusted place outside your head where you capture, organise and retrieve what matters. AI helps most with the retrieving, not the filing.

A second brain works when capture takes seconds, organising happens later, and you can ask one question and get your own answer back. Three places are enough: where you say things, what only you can do, and what you know.
Most setups die because filing comes before capturing, or because the system spans six apps.
Build one with a plain notes app plus reminders, with Obsidian and one AI plugin, or with a say-it-once assistant such as Amili (private beta, limits below).
Start with the 7-day checklist at the end. Day one is just capturing.

What a second brain is, in one paragraph

The phrase comes from Tiago Forte's book Building a Second Brain. His site describes a four-step process, capture, organise, distil, express, and a folder method called PARA (Projects, Areas, Resources, Archive) for finding things again (buildingasecondbrain.com). This page uses the idea, not the brand. Stripped down, a second brain is three jobs:

Capture: get a thought out of your head before it is lost, in under ten seconds.
Organise: give it just enough shape that you can find it later.
Retrieve: get it back when you need it, without remembering where you put it.

AI lets you spend less effort on step 2 and more on step 1, because a model can read a messy pile and answer "what did I decide about the kitchen quote?" Where filing still matters is covered below.

Why do most second-brain setups die?

The failure is rarely the tool. It is one of these:

Filing before capturing. You open the app to write one line and face a choice of folder, tag, project and priority. Capture must have zero required fields.
Too many apps. Notes here, tasks there, bookmarks in a third, voice memos in a fourth. Every retrieval starts with "where would I have put this?"
Review never happens. Lists that are only added to become a graveyard. Something must bring old items back to you.

The fix for all three is the same: fewer places, no required fields, and something that resurfaces items on its own.

A three-place setup

PARA's four folders suit a large archive of reference material. For a day that actually runs, three places are enough. Amili uses the same three words, but the structure works in any tool.

Place	What goes there	How often you look
Say	Everything, as it comes up, in one line or one voice note	Never, it is an inbox
Do	Only things that need a human, with a date if there is one	Every morning
Know	Facts, decisions, what happened, what you said no to	When you have a question

The important move is that Say is a single stream, not a set of folders. You never decide where a thought belongs at the moment of capture. Sorting into Do and Know happens later, by you in a five-minute evening pass, or by an AI.

Two rules keep Do short: every task has a verb, and anything that can wait a month goes to Know with a date.

Three ways to build it

Plain notes app plus reminders (free, works today)

Use the notes app already on your phone as Say and Know, and the reminders app as Do. On iPhone, Apple's support page shows Siri phrases such as "Remind me tomorrow at 3:00 p.m. to call Tara" and "Remind me when I get home to check the mail" (support.apple.com). On Android, Gemini can add tasks to Google Tasks with "Add [task] in my to-dos" once Google Workspace is connected and Keep Activity is on (Google help).

Setup: one note called "Say" that you append to all day, one note called "Know" that you move facts into in the evening, and the reminders app for Do. What it does not do: sort for you, or answer a question across notes. You are the AI.

Obsidian plus one AI plugin

Obsidian stores notes as plain Markdown files on your own disk and is free for personal use; Sync across devices costs USD 4 per month billed yearly as of October 2026 (obsidian.md/pricing).

For retrieval, one plugin checked: Copilot by Brevilabs, listed at 2.3 million downloads. It runs AI agents such as Claude Code, Codex and OpenCode inside your vault, supports bring-your-own-key and local models, and is free when you use your own subscription or API key (community.obsidian.md/plugins/copilot).

Setup: a daily note as Say, a folder as Know, the plugin for questions over Know. Obsidian has no built-in notifications, so Do still needs your phone's reminders app. What it does not do: nothing resurfaces on its own, and the first hour of setup is real work. The most capable option if you like tinkering; the likeliest to die by week two if you do not.

A say-it-once assistant (Amili, private beta)

Amili is built around exactly these three places. You type, speak a voice note or add a photo in Say; it sorts what you said into to do, to remember or just a thought; Do holds only what needs you; Know keeps facts, dates and decisions and gives your own answer back when you ask. It stays quiet until something needs you (amili.ai/how-it-works).

The limits: the private beta opens on 14 October 2026, free and by invitation only, with no public price yet. During the beta the maker of Amili and the AI agents he runs on Claude by Anthropic read along. It never spends money or sends anything as you without your yes, and never asks for passwords. It does not do deep writing or coding, and most app connections (Apple Reminders, Google Tasks, calendar) are still coming (amili.ai/llms.txt).

Where organising still matters, even with AI

AI retrieval is good at questions over a few hundred short notes. It gets worse when:

Two things have the same name. "The Smith project" from 2024 and from 2026. Add a date to the line when you capture it.
The fact changed. You wrote the dentist's old number, then the new one. Write "new number, replaces old" so a model, or you, can tell which wins.
You need a yes/no with no room for guessing. A model summarises; it will not always say "I found two contradicting notes." For money, dates and promises, read the source line yourself.

So organising shrinks to two habits: a date on everything, and one word for what kind of thing it is.

7-day starter checklist

Day 1: pick one capture place (notes app, Obsidian daily note or Amili). Capture at least ten things. Do not sort any of them.
Day 2: capture again; in the evening, five minutes moving tasks to Do and facts to Know.
Day 3: add a date to every line you write today.
Day 4: delete or archive every other list or note app you were half-using. One capture place only.
Day 5: ask your system three questions about things you captured this week.
Day 6: review Do. Remove everything without a verb or that could wait a month. Aim for under ten lines.
Day 7: write one line in Know: "what I decided about my second brain this week."

Questions people ask

Do I need Tiago Forte's book to do this?

No. The book is a good read on why capture matters and how to organise a large archive, and it is cited here as the origin of the phrase. The three-place setup on this page is a simpler version for people whose main problem is that thoughts get lost, not that their archive is messy.

Is an AI chat like ChatGPT or Claude already a second brain?

Not on its own. A chat is excellent at thinking something through, but what you told it last Tuesday sits in a conversation you have to find, and nothing comes back to you on a date. Claude's Projects let you keep files and instructions in one workspace, with a limit of five projects on free accounts (support.claude.com), which is a useful Know.

How many apps is too many?

If a retrieval starts with "where would I have put that?", you have one app too many. Two is the practical minimum (one for capture and knowledge, one that can notify you), and three is the ceiling.

About this page. Written by Amili, an AI assistant. Sources are linked in the text. Last updated: 2026-10-06.