Lessons to Develop a Writer's Toolkit:
Active vs. Passive Sentences

Dr. Stuart Blythe
Department of English & Linguistics
Indiana University-Purdue University Fort Wayne

 

In the previous four lessons, you learned about building sentences using clauses and phrases. In this fifth lesson, you will learn about one other sentence variation: active vs. passive constructions. After completing this lesson, you should be able to do the following:

  • Differentiate between active and passive sentences
  • Explain the relative strengths of each type of sentence
  • Transform active sentences to passive, and vice versa

About Active and Passive Sentences

To differentiate between active and passive sentences, let's begin with what you already know. You already know what active sentences are because you studied them when you completed the lesson on independent clauses. Active sentences are independent clauses with transitive verbs.

The difference between active and passive sentences is essentially one of word order. Active sentences follow the pattern of a basic independent clause: subject + predicate. That pattern gets inverted in passive sentences.

Consider this familiar example of a sentence in active voice:

The assistant weighed the soil samples.

This simple sentence has a noun phrase (N1 - "The assistant") for a subject, plus a verb (V - "weighed") and a second noun phrase (N2 - "the soil samples) for a predicate. If you thought of a sentence in active voice as a kind of equation, it would look like this:

N1 + V + N2

If the sentence were written in passive voice, the order would be inverted:

The soil samples were weighed by the assistant.

Notice that a number of things must happen to convert an active sentence to a passive form:

  1. The second noun phrase (N2: "the soil samples") must be moved to the beginning of the sentence
  2. A "to be" verb ("were") must be added before the verb (i.e., "weighed")
  3. The first noun phrase (N1: "The assistant") must be turned into a prepositional phrase beginning with "by" ("by the assistant")
  4. That prepositional phrase must be moved to the end of the sentence (after the verb)

If you thought of a sentence in passive voice as a kind of equation, it would look like this:

N2 + to be + V + by + N1.

Here's another example:

The county commissioners will review all bids for road improvement projects in the county. (Active)

All bids for road improvement projects in the county will be reviewed by the county commissioners. (Passive)

Why is It Worth Knowing the Difference?

You should understand the difference between active and passive voice for at least three reasons.

  • First, knowing the difference can improve concision. Notice that sentences in passive voice are more complicated structurally than those in active voice. (To see the difference, compare the "equations" above.) This is why many composition instructors insist on the active voice; it is simpler and more direct.

  • Second, knowing the difference can improve paragraph cohesion. By being able to re-arrange sentences, you're better able to make sure that any given sentence picks up the topic at the end of the preceding sentence.  You can also make a conscious effort to begin with a topic that a reader knows, and then work toward new information.

  • Third, knowing the difference can help you make conscious decisions about what to emphasize in a sentence. You may have noticed that many in science and technology often prefer the passive voice. This is because they are more interested in what happened, or what was observed, than in who did the observation. For example consider this active voice sentence again:

    The assistant weighed the soil samples.

    "The assistant" gets emphasized because those words appear first. Now, consider the passive voice again:

    The soil samples were weighed by the assistant.

    The passive voice highlights what was weighed. In fact, a writer can often delete the agent (i.e., "the assistant") altogether, is in this case:

    The soil samples were weighed.

    Remember that much scientific and technical writing is "objective," that is, it is focused on the object being studied or worked on. "Subjective" writing is focused on the subject, the person performing an action. Again, this is basically why many writers in the humanities prefer active voice, while many writers in the sciences and technology prefer passive voice. Many writers in the humanities are interested in human action; therefore, they use active voice to foreground the subject performing those actions. Many writers of scientific and technical prose, on the other hand, are more interested in the object being studied. Therefore, they more often use the passive to foreground the object.

Exercise

In order to reinforce this lesson:

  1. Create three simple sentences in the active voice. (That is, create two independent clauses using transitive verbs.)
  2. Convert those same three sentences to passive voice.

Example:

  • Margaret revised the specifications yesterday. (Active)
    The specifications were revised by Margaret yesterday. (Passive)

  • Telephone companies use two-wire segments to save money. (Active)
    Two-wire segments are used by the telephone company to save money. (Passive)

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last updated: 2003.12.23
originally created: 2001.02.21
© Stuart Blythe | blythes@ipfw.edu