Normal Tense

Intent

Convert verbs to present tense if possible (and appropriate).

Motivation

Verbs can express the relative timing of an event in the past, present, or future. Verbs with past tense indicate an event occurred (or the state resulting from the event). Verbs with present tense indicate the unfolding of a current event. Verbs with future tense indicate an event can (potential) or will (imperative) occur.

a predator captures its prey (action)
an employer employs an employee (relationship)
a wife married her husband (event, state)
a recipient will receive a message from its sender (event)

Applicability

Use present tense when

• you've isolated an active verb,
• especially a transitive verb that describes
  • an action of an actor,
  • a responsibility of a role, or
  • a relationship between its participants.

Use past tense only as a descriptive adjective when

• you've identified a state that follows directly from an event (an action or activity).

Use future tense only when

• you're formulating software requirements that use an imperative mood.

Considerations

Object-oriented designs tend toward use of the present tense for actions and relationships, especially for expressing the responsibilities of collaborators. Therefore, the normal form recommends, but does not require, the use of present tense for verbs. While present tense may be preferred for most statements, it's important to find the appropriate tense.

Many requirements specifications adopt the use of future tense with imperative mood to express individual requirements, especially using the auxiliaries will or shall. You can easily insert these auxiliaries into sentences that use present tense if needed (e.g., in a proposal or statement of work). But, they are not generally useful in the context of conceptual models of problem domains.

Verbs that indicate an event or a state will often be expressed in the past tense because they indicate an action that occurred to bring about the indicated state. In this case, the past tense verb will be retained as a descriptive adjective (describing an object state), while the present tense verb will be used to indicate how an object arrives at that state.

Consequences

A normal form sentence has a present tense verb with a complete predicate, singular number, active voice, indicative mood, and affirmative polarity. In English, a relationship exists between the tense of a verb and its mood. The following table explores this relationship.

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