From Grammar Girl http://grammar.quickanddirtytips.com/active-voice-versus-passive-voice.aspx
Today's topic is active voice versus passive voice.
Here's a question from Brian in Iowa. He writes, “It drives me crazy when people write in passive voice. How can I teach people how to tell the difference between passive and active voice and to stay away from passive voice?”
Well, Brian is right, the first step is to help people understand the difference between active and passive voice, because many people believe they should avoid the passive voice, but fewer people can define it or recognize it.
What Is Active Voice?
I'll start with active voice because it's simpler. In an active sentence, the subject is doing the action. A straightforward example is the sentence "Steve loves Amy." Steve is the subject, and he is doing the action: he loves Amy, the object of the sentence.
Another example is the title of the Marvin Gaye song “I Heard It through the Grapevine.” "I" is the subject, the one who is doing the action. "I" is hearing "it," the object of the sentence.
What Is Passive Voice?
In passive voice, the target of the action gets promoted to the subject position. Instead of saying, "Steve loves Amy," I would say, "Amy is loved by Steve." The subject of the sentence becomes Amy, but she isn't doing anything. Rather, she is just the recipient of Steve's love. The focus of the sentence has changed from Steve to Amy.
If you wanted to make the title of the Marvin Gaye song passive, you would say “It was heard by me through the grapevine,” not such a catchy title anymore.
Is "To Be" a Sign of a Passive Sentence?
A lot of people think all sentences that contain a form of the verb “to be” are in passive voice, but that isn't true. For example, the sentence "I am holding a pen" is in active voice, but it uses the verb “am,” which is a form of “to be.” The passive form of that sentence is "The pen is being held by me."
Notice that the subject, the pen, isn't doing anything in that sentence. It's not taking an action; it's passive. One clue that your sentence is passive is that the subject isn't taking a direct action.
Is Passive Voice Always Wrong?
Passive voice isn't wrong, but it's often a poor way to present your thoughts.
Another important point is that passive sentences aren't incorrect; it’s just that they often aren't the best way to phrase your thoughts. Sometimes passive voice is awkward and other times it’s vague. Also, passive voice is usually wordy, so you can tighten your writing if you replace passive sentences with active sentence.
When you put sentences in passive voice, it's easy to leave out the person or thing doing the action. For example, "Amy is loved," is passive. The problem with that sentence is that you don't know who loves Amy.
Politicians often use passive voice to intentionally obscure the idea of who is taking the action. Ronald Reagan famously said, “Mistakes were made,” when referring to the Iran-Contra scandal. Other examples of passive voice for political reasons could include “Bombs were dropped,” and “Shots were fired.” Pay attention to the news and listen for examples of passive voice.
Also, a reader named Matthew commented that businesses sometimes use passive voice. He notes that it sounds better to write, "Your electricity will be shut off," than "We, the electric company, will be shutting off your power."
Is Passive Voice Hard to Understand?
A recent study suggests that less educated people--those who dropped out of school when they were 16--have a harder time understanding sentences written in the passive voice than those written in active voice. I only had access to the press release, not the original study, but the results made it seem as if you should stick with active voice if you're writing for the general population.
Is Passive Voice OK in Crime Reports?
On the other hand, sometimes passive voice does have advantages. For example, if you truly don’t know who is taking the action, then you can’t name the person. This is especially common with crime reports. For example, a security guard might write "The store was robbed," because nobody knows who the robber was.
Can Passive Voice Work in Fiction Writing?
Passive voice is also sometimes useful in fiction writing. For example, if you were writing a mystery novel and you wanted to highlight missing cookies because they are central to the story, passive voice is the best option. It would make more sense to write, "The cookies were stolen," instead of "Somebody stole the cookies."
The difference is subtle, but in the passive sentence “The cookies were stolen,” the focus is on the cookies. In “Somebody stole the cookies,” the focus would be on the unknown somebody.
Passive voice can be helpful if you want to create a sense of mystery in your sentence, which is also a reason that it's not usually a good choice when you're writing nonfiction and you want your writing to be clear.
Why Is Passive Voice Recommended for Science Writing?
An exception is that scientists are often encouraged to write in passive voice to lend their writing a sense of objectivity--to take themselves and their actions and opinions out of the experimental results. I used to be a scientist and I always found that odd. It felt as if we were trying to hide that real people did the experiments.
Some scientific style guides do allow for a limited use of active voice (1). For example, it may be OK to write, "We sequenced the DNA," instead of "The DNA was sequenced," but it's still considered bad for scientists to insert themselves into conclusions. For example, it would be bad scientific form to write "We believe the mutation causes cancer." But you still don't need passive voice to achieve your goals. For example, the active sentence "We believe the mutation causes cancer," could be changed to "The data suggests that the mutation causes cancer." That's still active, but it eliminates the sense of subjectivity.
Did Strunk & White Get Passive Voice Wrong?
Finally, I have to include a note about Strunk & White’s treatment of passive voice. In their classic book, The Elements of Style, three of their four examples of passive voice aren’t actually passive voice sentences. I’ve included two links below that explain the problems, but if you rely on The Elements of Style, as so many people do, be aware that this is a problem with that book.
50 Years of Stupid Grammar Advice (The Chronicle of Higher Education)
English Passive Voice (Wikipedia)
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You can also always find more great Grammar Girl articles in the archives.
Web Bonus: Watson & Crick
Watson and Crick's famous paper about the discovery of the structure of DNA, written in 1953, contains both active and passive sentences;
We wish to suggest a structure for the salt of deoxyribose nucleic acid (D.N.A.). (active)
We have made the usual chemical assumptions, namely, that each chain consists of phosphate diester groups joining beta-D-deoxyribofuranose residues with 3',5' linkages. (active)
If it is assumed that the bases only occur in the structure in the most plausible tautomeric forms (that is, with the keto rather than the enol configurations) it is found that only specific pairs of bases can bond together. (passive)
It has been found experimentally that the ratio of the amounts of adenine to thymine, and the ratio of guanine to cytosine, are always very close to unity for deoxyribose nucleic acid. (passive)
In most English sentences with an action verb, the subject performs the action denoted by the verb.
These examples show that the subject is doing the verb's action.
Because the subject does or "acts upon" the verb in such sentences, the sentences are said to be in the active voice.
One can change the normal word order of many active sentences (those with a direct object) so that the subject is no longer active, but is, instead, being acted upon by the verb - or passive.
Note in these examples how the subject-verb relationship has changed.
Because the subject is being "acted upon" (or is passive), such sentences are said to be in the passive voice.
NOTE: Colorful parrots live in the rainforests cannot be changed to passive voice because the sentence does not have a direct object.
To change a sentence from active to passive voice, do the following:
1. Move the active sentence's direct object into the sentence's subject slot
2. Place the active sentence's subject into a phrase beginning with the preposition by
3. Add a form of the auxiliary verb be to the main verb and change the main verb's form
Because passive voice sentences necessarily add words and change the normal doer-action-receiver of action direction, they may make the reader work harder to understand the intended meaning.
As the examples below illustrate, a sentence in active voice flows more smoothly and is easier to understand than the same sentence in passive voice.
It is generally preferable to use the ACTIVE voice.
To change a passive voice sentence into an active voice sentence, simply reverse the steps shown above.
1. Move the passive sentence's subject into the active sentence's direct object slot
2. Remove the auxiliary verb be from the main verb and change main verb's form if needed
3. Place the passive sentence's object of the preposition by into the subject slot.
Because it is more direct, most writers prefer to use the active voice whenever possible.
The passive voice may be a better choice, however, when
- the doer of the action is unknown, unwanted, or unneeded in the sentence
- the writer wishes to emphasize the action of the sentence rather than the doer of the action
- the writer wishes to use passive voice for sentence variety.