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The Value of the Passive Voice

When should an author choose the passive voice over the active voice? What is the difference between them?

The passive voice emphasizes the person or object receiving the action (e.g., Samples were analyzed). The active voice, in contrast, emphasizes the person or object performing the action (e.g., We analyzed samples).

Because active-voice sentences are clearer, livelier, and often more concise than passive-voice sentences, most style guides advise scientific authors to prefer the active voice in their writing.

Notice though, that the recommendation is not to write entirely in the active voice. An all-out active writing style would be just as difficult to read as an all-out passive style: balancing the two perspectives is key.

Other than to add variety, when is the passive voice the better choice? Here are three good reasons to use it.


1. The performer is unknown, irrelevant, or obvious

The passive voice is preferable if the performer cannot easily be named or if the performer is irrelevant to the discussion, as in the following examples:

Up to 90% of the energy in light bulbs is wasted in the form of heat.

The first edition of Freud's earliest writings on dreams was published in 1899.

Drosophila melanogaster has been one of the most extensively studied species in genetics research.


In the first sentence, the author's attempts to name the performer would be awkward; in the second sentence, the author assumes the reader will not be interested in the name of the publisher; and in the third sentence, the performer (researchers) is obvious.

When naming the performer would prove difficult or unnecessary, the passive voice works well.


2. The performer is less important than the action

When discussing an experimental procedure in the Methods section, a researcher might write:

The honey bees were kept in a humidified chamber at room temperature overnight.

The solution was heated to 90°C for approximately 30 minutes and then allowed to cool.


The sentences could be converted to active voice by writing the following:

We kept the honey bees in a humidified chamber at room temperature overnight.

We heated the solution to 90°C for approximately 30 minutes and then allowed it to cool.

Does the active voice shorten the sentences? No. (In fact, the second sentence is one word longer than it is in the original version. The active voice is not automatically more concise than the passive.) Does the active voice add clarity? Perhaps, although the reader may be justified in assuming that the authors are also the performers.

The active voice has changed the focus, however, from the research to the researchers, an emphasis the author may not desire in the Methods section, where the general topic is the research materials and procedures.

On the other hand, if an author does emphasize the active voice over the passive in the Methods (or any section), most sentences will begin with we, which is distracting when overdone.1 In that case, passive style sentences vary the structure and rhythm while keeping the emphasis on the work.

Whether in the Methods or elsewhere in a manuscript, the passive voice redirects attention to the action (or the recipient).


3. The recipient is the main topic

Choosing a passive writing style is sometimes necessary to position important information at the beginning or end of a sentence.

For instance, the subject (person, thing, or idea) that the author wishes to discuss in a sentence should occur near the beginning in the topic position where the reader expects to find it ("first things first").2

The following active-voice sentence begins a new section in which the topic is "green plants" (the performer):

Green plants produce carbohydrates in the presence of light and chlorophyll.

If, on the other hand, "carbohydrates" (the receiver of the action) is the opening topic, the sentence is better written in the passive voice:

Carbohydrates are produced by green plants in the presence of light and chlorophyll.


The topic of a sentence is not an isolated island, however—it has context in relation to the surrounding sentences and paragraphs.

The topic must not only identify the subject for the reader, but it must prepare the reader "for upcoming material by connecting it backward to the previous discussion."2

For example, look at the first three sentences of a classic article written by Watson and Crick in 1953:

We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). This structure has novel features which are of considerable biological interest.

A structure for nucleic acid has already been proposed by Pauling and Corey.3


Notice that the authors used the active voice in the first and second sentences, but the passive in the third. If the third sentence is changed to active voice, it becomes:

Pauling and Corey have already proposed a structure for nucleic acid.

This revision shortens the sentence and identifies the performers. However, the original passive style creates parallel structure by repeating the topic of the second sentence ("This structure has...") in the third sentence ("A structure for..."). The topic in the third sentence connects backward and prepares the reader for the upcoming information. These three sentences are more cohesive as a result.

By focusing on the topic, the authors have incorporated the passive voice to advantage, producing a passage that flows naturally and is comprehensible and enjoyable for the reader.


Summary

Just as varying the sentence length in your scientific manuscript creates more variety and interest for your readers, so, too, does using both active and passive voice.

Choose the active voice whenever possible.

Choose the passive voice if you have a good reason to do so. Consider passive voice when:

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


You can also use the passive voice to hedge (i.e., to be noncommittal).

However, that is one use that cannot be recommended. (That is an example of hedging!)


Sources


  1. Zeiger M. Essentials of Writing Biomedical Research Papers. 2nd ed. New York, NY: McGraw-Hill; 2000.


  2. Gopen GD, Swan JA. The science of scientific writing. Am Scientist. 1990;78:550-558.


  3. Watson JD, Crick FHC. Molecular structure of nucleic acids. Nature. 1953;171:737-738.


Do you have a question on this writing tip? Contact me online and I'll be happy to help.

For information on scientific and medical editing, please visit Science Editing Services.







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