Definition

A definitional condition of a scoped transition: without it, an instance isn't an instance of the transition.

The definitional test

Essential characteristics are identified by removal: take a candidate characteristic out of the resulting state of an instance and ask whether the user would still consider the transition to have happened. If yes, the characteristic isn't Essential. If removing it would make the user say "no, that's not what I was trying to accomplish," it is.

Essential characteristics are the cleanest discrimination criteria a transition has. Two instances that share every other characteristic but differ on one Essential characteristic are different transitions. A single Essential miss is what separates "sent an invoice" from "drafted an invoice."

The three tiers in context

Essential is one of three tiers in condition tiering, the operation that sorts candidate characteristics of a named transition by definitional role:

• Essential: definitional — if absent, the instance isn't an instance of the named transition.
• Expected: typical — present in most instances by default; absent cases are diagnostic but don't exclude.
• Related: correlated — plausible in the transition, not central to whether the instance belongs.

The three tiers do different discrimination work. Essential conditions cleanly separate transitions; Expected conditions give probabilistic signal; Related conditions are weakly indicative. Distribution typically runs small Essential pile, slightly larger Expected pile, larger Related pile.

How Essential becomes completion criteria

Completion criteria are the Essential tier made operational — specified as IF-conditions of the resulting state that must hold for the transition to count as complete. The Essential tier identifies which characteristics are definitional; completion criteria put them into the form the route and scope-translation apparatus can operate on.

Expected and Related characteristics don't become completion criteria. They inform auxiliary route and the affordance-landscape thinking around the critical route minimum, but they aren't required for the transition to count as complete. Treating an Expected or Related characteristic as Essential over-loads completion criteria and narrows the transition until valid instances stop counting; treating an Essential characteristic as Expected discards the line that separates the transition from adjacent ones.

Where candidates come from

The operation is source-agnostic. Candidates can come from qualitative user investigation, team elicitation, or common-parlance decomposition of socially-defined transitions. The sticky-note exercise is the canonical team-facing method: generate one idea per sticky note for a high-level activity, then sort the notes into the three tiers. The Rosie-the-Robot test is the analyst-facing complement: imagine the transition's output produced competently, then list the conditions under which you would reject it. Both methods converge on the same set when run completely; they enter the work from different starting positions.

Example

For the named transition "sent first invoice" in an invoicing-SaaS context:

• Essential: invoice was transmitted to a recipient; invoice includes an amount due. Without these, the transition didn't happen — the user has at best a draft.
• Expected: line items breaking down the work, payment terms, due date specified. Usually present; absent cases are diagnostic but the invoice still counts as sent.
• Related: branded styling, custom thank-you note, invoice saved as a template for next time. These color the transition without determining whether it happened.

The Essential tier becomes the completion criteria for "sent first invoice." A user who satisfies those conditions has reached the transition's resulting state regardless of whether their invoice carried a logo.

See also

• Starting state
• Sorting hat design
• Transition scoping