Saying what the work is for
| The Principia Machina: map |
|---|
| Reading the diagrams Structure key Process key Definition of terms Roles |
| Reading by audience Start here: the walk through The operator's guide Tutorial: create a UUID Workspace Container (UWC) Public Recorder inputs Sponsors: your first agent |
| The specification Contents: parts, tables, diagrams TPS 0.5.0 (declared 2026-10-03, revision 8; machine-optimized text) Decisions (the foundations record, one line each) |
The GTP walk, page 6 of 6. Written for the general reader; nothing here is a rule, and every rule it mentions is stated by the specification, which governs wherever the two differ.
Saying what the work is for
Every project produces something, and every project has machinery for producing it. Those are two different kinds of thing and they call for two different kinds of choice, which is easy to agree with in the abstract and easy to get wrong in practice.
The distinction is drawn by asking what the project exists to make. Whatever that is, it is the front of the house. Everything that exists in order to produce it is the back. The line falls in a different place for every project, and the same sort of object can be on either side of it.
This project is a clean illustration. The Principia Machina is a project for building an instrument that tests physics, not a project for doing physics. So the machinery is what it exists to produce, and the machinery is the front of the house. The physics content the instrument eventually yields is the back. That sounds inverted until you remember which project this is, and the moment it stops sounding inverted is the moment the distinction has been understood.
The diagram sets out both sides and what happens to an item on each.
The Principia Machina/Diagrams/P06 The front-end contract The two sides of a project and how an item on each is ranked. (diagram page.)
Choices about the front are ranked by a rule the project writes for itself and states in the open. Here that rule puts correctness first, in a particular and unforgiving sense: if a proposal lets a check accept something the check ought to reject, the proposal is out. Not ranked lower. Out. Second comes how many opportunities a design hands a human being to make a mistake, counted, because opportunities taken are proportional to opportunities offered. Cost comes third and only breaks ties.
Choices about the back are ranked the same way in every project: how recoverable the thing is if it goes wrong, how far the damage reaches, and what it costs. No project gets to invent its own answer to those.
A project has to write its membership and its ranking down before either can be used. Until it does, items about the front of the house do not get ranked at all. They stop and say what is missing. The alternative is an agent quietly inventing a standard and then applying it consistently enough to look principled, which is the failure this rule exists to prevent.
Some things are placed outside the ranking altogether and declared untouchable. Here it is the separation that keeps certain acts in human hands: a named person declares what the kernel says, what state a container is in, and when a piece of work is finished. That separation is expensive by the second measure, since it is a human operation every time, and no efficiency argument is allowed to reach it. Naming such things explicitly, in the same document as the ranking, is what stops them being optimised away one small reasonable step at a time.
That is the walk. What remains is procedure: the operator's guide takes the same ground in the order a person works through it, and the instruction set itself states every rule these six pages have only described.
Previous: Keeping the pieces in step. Next: the operator's guide.