Gulf of execution and gulf of evaluation

The terms gulf of execution and gulf of evaluation were introduced by usability researcher Donald Norman. They are concepts that are essential to understanding the interaction between humans and computers. The two gulfs are closely related to Norman’s Seven Stages of Action; the first four stages make up the gulf of execution, while the next three stages make up the gulf of evaluation. Consider the diagram below:

Gulf of execution

Gulf of execution is the degree of ease with which a user can understand the current state of a system. It is the difference between the intentions of the users and what the system allows them to do.

For example, a person can look at a light switch and easily tell what the current state of the system is (i.e., whether the light is on or off) and how to operate the switch. This means that the gulf of execution is small. Norman states that, in order to design the best interfaces, the gulf must be kept as small as possible.

Gulf of evaluation

Gulf of evaluation is the degree of ease with which a user can perceive and interpret whether or not the action they performed was successful. This gulf is small when the system provides information about its state in a form that is easy to receive, interpret, and matches the way the person thinks of the system.

Consider the same light switch example; if a person looks at a light switch, the gulf of evaluation is very small since, with one switch, the user will immediately know if their action was successful. An example of a large gulf of evaluation is when an application has a spinning wheel to show a “loading” state after the user performs an action. The wheel alone is not enough for the user to interpret the progress that ​the system is making in response to their action. The gulf can be shortened by having a loading bar instead.