Passive voice

Explanation

In English grammar, verbs have two voices: active voice and passive voice. In active voice, the subject of the sentence performs the action. In passive voice, the subject is acted on.

Passive voice emphasizes the object and the action instead of the actor. Typically, you use passive voice if the actor is unknown or less important than the action.

• Active voice: The developer implements the requirement.
• Passive voice: The requirement is implemented by the developer. OR The requirement is implemented.

To identify passive voice, look for a form of the verb be (such as is, are, were, have been) plus the past tense of the main verb.

• Examples: is allowed, is controlled, is displayed, is output, is provided

A requirement in the passive voice can be grammatically correct, but can be confusing if the actor is unclear or not stated. Sentences in active voice clearly identify the actor, and are often more direct and succinct than sentences in passive voice.

Example 1

Consider the following requirement, which is written in passive voice:

• The height of the aircraft above sea level shall be displayed.

This sentence is grammatically correct. However, the requirement doesn’t communicate the actor in the sentence: who or what will display the reading.

The following requirement communicates an actor, but is still written in passive voice:

• The height of the aircraft above sea level shall be displayed by the dashboard module.

Although this sentence is also grammatically correct, it places the emphasis on the action and not on the actor.

Voice is important in requirements because a requirement must clearly state the actor. A requirement is incomplete if it does not specify the actor: who or what performs the function. Sentences in the active voice put the actor (person or thing) that performs the action first. In active voice, the actor is essential to and the focus of the sentence.

The following requirement is written in active voice:

• The dashboard module shall display the height of the aircraft above sea level.

This active version clearly states what will perform the action, and more directly and succinctly expresses the requirement than the passive versions.

Example 2

Requirements might use passive voice if one actor performs several tasks in multiple requirements that are documented sequentially. Often, the actor is mentioned in the first requirement and omitted from subsequent ones.

• The dashboard will be displayed by the system when the user presses F3.
• An alarm will be sounded simultaneously.

When you read the requirements together, the second requirement makes sense. However, in an automated tool, requirements can be separated. Each requirement must be complete and self-sufficient, which is why active voice is preferred. Active voice forces the author to include the requirement actor.

• The system will display the dashboard when the user presses F3.
• The system will sound an alarm when the user presses F3.

Now, the second requirement makes sense on its own, even when it’s separated from the first requirement.