Gulfs of Execution and Evaluation

Two gaps a person must bridge when using something. The Gulf of Execution is the gap between an intention and the actions the system allows ("how do I do this?"). The Gulf of Evaluation is the gap between the system's actual state and the user's understanding of it ("did it work?").

Why it Matters

Usability problems live in these gulfs. Good signifiers and mappings bridge the execution gulf; good feedback and a clear conceptual model bridge the evaluation gulf.

Signals

• Users cannot translate a goal into actions (execution gulf).
• Users cannot tell what state the system is in or whether their action succeeded (evaluation gulf).

Benefits

A precise diagnostic for where a design breaks down and which principle to reach for.

Risks

Closing one gulf while ignoring the other; assuming the user shares the designer's view of the system state.

Tensions

Bridging the execution gulf can add controls and bridging the evaluation gulf can add feedback; both risk clutter when overdone.

Examples

Not knowing which gesture performs an action (execution); not knowing whether a file actually saved (evaluation).