Use of Passive and Active Voice

Introduction
A sentence in active voice identifies the performer and describes them doing an action. "Dog bites man." uses active voice.

A sentence in passive voice identifies the action and object and attributes a performer either explicitly or implicitly. "Man bitten by dog." uses passive voice.

Writers are encouraged to use active voice whenever possible. Passive voice has an important place, such as in the previous sentence.

Schemata and Cognitive Load
Voice determines how a text gives information to a reader. All writing functions because of schemata, the mental frameworks and expectations which are implicit in your audience. English, as a language, communicates best to readers when following the Subject Verb Object pattern. As such, readers function in that schema and expect writing to follow a Subject Verb Object pattern.

Using the passive voice makes interferes with this pattern. If you were to say “The transistor was connected”, you would be failing to explain who connected the transistor and to what they connected a transistor. A reader, working in the Subject Verb Object schema, would then have to substitute another schema to fill in the blanks.

An engaged reader may still be able to infer the meaning of a passive sentence from context, but it asks them to perform an additional step which increases cognitive load. Psychologist George Miller identified limits in a reader’s working memory, stating that a typical person could hold only between 5 and 9 categories of information at a time. When asking readers to engage in already complex technical information, taxing their working memory through unintuitive sentence structure significantly slows the reader.

Passive voice is necessary, however, in certain circumstances. Hupet and LeBouedec, working in 1975 for the Quarterly Journal of Experimental Psychology, identified situations in which the passive voice was in fact clearer than the active. These constructs, known as cleft sentences, are compatible with the schema of Subject Verb Order because they utilize points established earlier in the writing.

Exceptions
Take for example the sentence “Connect the transistor to the circuit board.” This is active voice, identifies the speaker, and follows the Subject Verb Object schema. If later in the document, the sentence “All transistors will now be connected.” appears, that would be an appropriate cleft sentence. The document established earlier who connected the transistor and to what they connected it. Therefore, there is no additional cognitive load.

Alternately, cleft sentences highlight when the subject of the verb is unnecessary or unimportant. In scientific and technical writing, which often focuses on inanimate objects, the behavior and properties of that inanimate object may be more important than any person interacting with it.

In such situations, endlessly reaffirming that laboratory staff performed each step of the process repeatedly points the reader toward unnecessary information and away from the focus of the writing. This increases cognitive load. Barbara Every, of the BioMedical Editor blog, identifies three situations when passive voice reduces cognitive load.


 * 1) The performer is unknown, irrelevant, or obvious.
 * 2) The performer is less important than the action.
 * 3) The recipient is the main topic.
 * 1) The recipient is the main topic.
 * 1) The recipient is the main topic.

Technical writers should continue to use active voice unless doing so would create additional cognitive load. Awareness of these exceptions, however, will lead to clearer technical communication on complex topics.