What are the four parts of a working second brain?

Every second brain that falls over falls over the same way. Something inside it was given a job belonging to a different part, and nobody noticed until the day it mattered. A capture tool that decides what is worth keeping. A records folder that refuses a subject. A weekly report that writes into files. A drafting step with nothing between it and the outside world.

So the useful way to explain this is by the four parts and the lines between them. The lines carry the safety argument. Learn them and you can look at your own setup, whatever it is built from, and name the part you are missing.

First, what PAD means

PAD stands for People, Assets, Deals. Three folders of plain text files on your own computer, plus one plain document at the top that tells an AI assistant how to work inside them: where to file what, how to name it, what it may never do, and when to stop and ask.

• People. Humans, and the animals that belong to them. One file per person, forever, referenced from everywhere that person appears.
• Assets. Things that appreciate or decay depending on whether they are maintained. A rental, a website, a truck, a license, your own health.
• Deals. Work that closes. Participants, a stage, deadlines, and a day it ends. One folder each, holding call notes, documents and the decisions made inside it.

Part one: capture

Capture takes material in and holds it with nothing decided about it. A voice memo recorded in a truck. A photo of a scribbled page from a walkthrough. A forwarded email, a call transcript, a scan of a signed form. It records and it stamps, meaning it writes down what arrived and when, and then it stops.

Capture refuses nothing at all. No topic, no person, no subject. This is the first place people expect a filter, so it is worth being blunt about why there is none: a capture step that judges what is worth keeping loses material at exactly the moment you are too busy to notice. Nine at night after a long day is when the thing you most need to keep arrives.

In the shipped system the intake is enforced rather than promised, and that distinction is worth insisting on with anything in this category. The capture step has exactly two write paths. Both are checked against a resolved path immediately before the write, meaning the destination is worked out to its final form and then verified rather than trusted. Files are opened in create only mode, so a write can make a new file and can never quietly replace an existing one. A promise about where a system writes is a sentence in a document, and a document cannot fail. A check before every write holds or fails loudly.

Part two: the records

The records are the ledger of the business. People, Assets, Deals, and the decisions. This is the part you would still want if you deleted the other three.

The records refuse nothing either. Anything about a person, an asset or a deal belongs in them. What an agent knows about the people in her life is the thing this vault exists to hold, and a records system that will not hold it is a filing cabinet with opinions.

One part of the four is never automated, and this is it: a person decides what every item means. Machines can put an item in front of you and propose where it goes. The meaning is human every time. Whether the thing is settled or still a maybe. Whether the promise was yours or theirs. Whether the sentence she said in the driveway is the reason for everything that happens next year.

The status discipline lives here. Ideation for thinking out loud, evidence for something observed with a source and a date, decision for something carrying a date and the name of the person who made it. No status means ideation, and only the owner promotes anything to decision. The one thing the records never hold is a live number, because a price, a rate, a stage or a schedule lives in the system that changes it and the file says where to look.

Part three: the scan

The scan reads the records against themselves and asks about what does not add up. Two files giving different closing dates for one transaction. A number carrying a checked date from four months ago. A person nobody has contacted since February with an open promise sitting on their file.

Two constraints define it and both are absolute. The scan writes nothing. The scan rules on nothing. It produces a report made of questions, and every answer belongs to a person.

Be plain about the state of this part: in the current release it is designed and not shipped. The install page says so and this article says so. If you are running the system today, the scan is something you do by reading. The design is fixed already so that when it does ship, it cannot arrive carrying the ability to write, which is the most common way a records system starts producing entries nobody wrote.

Part four: the output check

The recipient half deserves its own paragraph. Anything that sends has exactly one recipient, fixed when the system was installed, and that recipient is the owner. It is never worked out from context, from a file, or from the message being processed. The reason is specific: on 2026-07-31 an automated brief containing private client information reached eighteen unintended recipients on a comparable system. The cause was never identified and no fix was documented. A recipient that cannot be resolved from data cannot be redirected by data.

Why the filter sits at the output and nowhere earlier

An agent knows about a client's divorce, because the divorce is why the house goes on the market in April. A loan officer knows a borrower's income to the dollar and the reason behind the collection account. A contractor knows a homeowner's budget, their marriage, and which of the two will change their mind about the tile in week three. None of that is optional knowledge somebody went looking for. It is the work.

A records system that refuses to hold that material does not cause it to disappear. It relocates it, into a phone note, a text thread, or the head of the one person who was in the room, and none of those has any check on it. The only open question is whether the material sits somewhere with a gate between it and the outside world.

So a system whose output layer refuses to emit something is a safer home for that material than a system with no output layer. A refusal at the recording step protects the tidiness of the folder. A refusal at the sending step protects the person.

One test follows, worth applying to any rule handed to you by any system, including this one. Ask whether the rule constrains what somebody is allowed to know, or what somebody is allowed to send. A constraint on knowing belongs at the drafting step or nowhere. A rule justified by the argument that recording something might cause a problem later is that error wearing a reasonable sentence, and it is convincing enough that this system carried one for about an hour on 2026-08-12 before the owner struck it.

The refusals at the output are hard ones. Where a brand in the records is marked as resident care, nothing about a resident leaves in a draft, a message or a document, and that covers a redaction, a summary and a count by name, because each is the same disclosure in a smaller box.

The boundaries, in one table

Every failure mode is a boundary crossed by the wrong part. Read the right hand column as a list of the ways this goes wrong.

How to work out which part you are missing

This runs against whatever you have today: a folder of files, a note app, a CRM and a phone, or nothing at all. Four questions, in order.

1. 01Where does something land at nine at night with nothing decided about it? If you have to work out where it goes before you can put it down, you have no capture step, and material goes missing on your busiest days.
2. 02Is there anything your records will not hold? If a category of thing lives somewhere else because writing it down felt risky, your filter is in the wrong part. Move it to the output and let the record hold the material.
3. 03What reads your records looking for things that do not add up? If the answer is you, on a good week, your scan runs at the frequency of your energy, which is the frequency at which it stops in a busy month.
4. 04What checks something before it goes out under your name? If the answer is nothing, you are relying on whoever is drafting being careful, and drafting happens in a hurry.

Most businesses we look at have a strong second part and nothing else. Capture is improvised, the scan is a person remembering, and there is no output check, because nobody knew it was a part.

What the four parts do not do

Four parts. One refuses things, one is never automated, one is not shipped yet, and one will hold anything you hand it. If you can name which of the four your own setup is missing, this article did its job, whether or not you ever install anything.