Your high-school English teacher forbade the passive voice verb construction in favor of spare, lively active voice. But your university science professor insisted on objective, impersonal passive voice. Now you’re writing about science. When should you use passive voice?
Most editors recommend against passive voice unless you want to emphasize results, describe a natural or mechanical process, or create a transition.
What is voice?
In active voice, the subject performs the action. For example: “The software generates a ranked list of possible peptides and proteins for each spot.” The subject, software, performs the action.
In passive voice, the subject receives the action. The grammatical construction for passive voice involves a form of the verb “to be” together with the past participle of a verb. For example: “A list of possible peptides and proteins for each spot is generated by the software.” The subject, list, receives the action, is generated. The actor in the sentence is the object of the preposition by.
Why is passive voice a problem?
Passive voice in scientific and technical writing is often considered dignified; lively writing seems, well, undignified. In a 1996 letter to the editor of Nature, chemistry professor Leon Avery says that “liveliness of style is the worst sin” in the scientific writing. Try telling a joke in a scientific paper, he suggests, and see what happens.
But lively writing is not your goal as a communicator; clear and concise writing is. And that’s the best reason for choosing active voice. Passive voice often results in unclear modifiers, unnecessary words, and ambiguity as to the agent of the action. The writer may view passive voice as dignified, but the reader often perceives it as a source of confusion.
When should you use active voice?
Use active voice when you need to be direct, clear, and concise. Use active voice for instructions, for example. In fact, use active voice most of the time.
Look again at our example from a biotech software guide: “The software generates a ranked list of possible peptides and proteins for each spot.” In this example, it’s important to know who or what generates the list, the user or the software. If you want to emphasize the actor in a sentence, use active voice.
When should you use passive voice?
Some writers use passive voice to describe a natural or mechanical process if the actor is irrelevant or unknown. (I’m including software processes in the definition of a mechanical process.) Use passive voice to emphasize the recipient of the action. And, use it for emphasis or to show transition from one topic to another.
Take, for example, the following figure caption: “Real-time PCR data with insufficient input gDNA. gDNA was added at concentrations ranging from 0.01 to 20 ng per reaction. At 40 cycles, many of the PCR reactions have not reached the plateau stage of PCR.” In this caption, who did the adding is not significant; gDNA is. Repeating gDNA at the beginning of the sentence after the caption phrase provides a transition to the explanation of why the input of gDNA was insufficient.
Passive voice can effectively emphasize results. When you deliberately choose passive voice, be sure to maintain parallelism; don’t start a sentence in active voice and then shift to passive. Avoid passive constructions that result in awkward or misplaced modifiers.
One final word of caution: Don’t recast an effective passive construction just because your English teacher (or your editor) told you to. This quote from Thomas Edison breaks all the rules, but it works:
Opportunity is missed by most people because it is dressed in overalls and looks like work.