In grammar, "voice" refers to the relationship between the subject and the verb—that is to say, how the action is performed. Active voice emphasizes the subject as the one performing the action. In contrast, passive voice deemphasizes the subject as performer and instead frames the subject as receiving the action.

Which voice you choose to use should depend on the type of writing and your audience. The active voice is more frequently used in non-scientific writing. Since it usually uses fewer words, it is more succinct and clearer than the passive voice. However, only using the passive voice in scientific writing can make it dry and bog down the reader. Choosing the proper voice will set the tone for your writing, but keep in mind that most writing will include both active and passive voice. 

Let's take a look at some examples.

Active and Passive Voice

In a sentence written in active voice, the subject's role in performing the action of the verb is emphasized. These sentences will generally follow the pattern of subject–verb–object (or simply subject–verb, for intransitive verbs—i.e., for verbs that don't need an object):

• The student [subject] finishes [verb] the exercise [object].
• Fred [subject] ate [verb] his sandwich [object].
• Eve [subject] survived [verb, no object needed].

In a sentence written in passive voice, the subject's role in performing the action of the verb is deemphasized. Instead, passive voice frames the subject as receiving the action. Passive voice is the opposite of active voice, so sentences in passive voice tend to follow the reverse pattern of object–verb–subject, and the word "by" often shows up between the verb and the subject:

• The exercise [object] was finished [verb] by the student [subject].
• The sandwich [object] was eaten [verb] by Fred [subject].

In most sentences in passive voice, you will see the word "by" between the verb and the subject. In fact, a rule of thumb for recognizing passive voice if you see the construction "was/is [verb]ed by" (for verbs like finished or started) or "was/is [verb]en by" (for verbs like eaten and forgotten).

Most sentences can be phrased to be in either active or passive voice. For example:

• Active voice: The teacher sent the student to the principal's office.
• Passive voice: The student was sent to the principal's office by the teacher.

Which one you choose may not significantly change the meaning of the sentence, but it will likely change its tone and emphasis. It is important to understand the connotations of both active and passive voice, therefore, so your sentences don't sound odd or out of context.

That said, sentences with intransitive verbs—verbs that do not take direct objects—cannot be passivized because there is no object to put before the verb. For example:

• Millions of people lived.
• We arrived yesterday.
• Shelly will be asleep.

Try to put these in passive voice (in the order object–verb–subject): "[Blank] was lived by millions of people." It doesn't make sense! Intransitive verbs can never be used in passive voice.

Most of the Time, Use Active Voice

Active voice is generally more direct and neutral than passive voice. Passive voice tends to sound evasive, like the writer is trying to avoid blame for whoever performed an action, or academic, like a dry science report. Active voice is generally more effective at capturing the reader's attention. For example, 

• Passive voice: The ball was hit by Linda. 
• Active voice: Linda hit the ball.
• Passive: The theme that was most commonly addressed by 17th-century writers was ...
• Active: 17th-century writers most commonly addressed the theme of ... 

The use of active voice is more direct and provides information about who performed the action.

Guidelines for Avoiding Passive Voice

1. Avoid sentences that use the verb "to be" or its variations (is, was, will be). The verb "to be" often describes what something is rather than what it does.
2. Avoid beginning sentences with "It is …" or "There are …"
3. Avoid sentences where the action is frozen in a word that ends with one of the following suffixes: -tion; -ment; -ing; -ion; -ance. These words mute the action that the verb should communicate by turning them into nouns.

Using Passive Voice Effectively

All that said, passive voice certainly has its uses—you just need to be smart about when you use it! For example:

• "Hamlet was written by Shakespeare." Here, the passive voice emphasizes "Shakespeare," the most important part of the sentence.
• "Jamey was fascinated by language arts." The passive-voice construction of this sentence emphasizes "Jamey" more effectively than the active-voice equivalent.
• "Smoking is strictly prohibited." Because a passive verb consists of two words, an adverb (like strictly) is accentuated when placed between "to be" and the past participle.

When Writing a Research Paper

In particular, scientific research writing often requires that the writer deemphasize themselves as the performer of the action. This makes the language more objective; in theory, an experiment should happen the same way and have the same results no matter who conducts it. For example:

• Active voice: I found that the frog population decreased by 10% last year.
• Passive voice: It was found that the frog population decreased by 10% last year.

When Talking about General Rules

Passive voice is also often used when talking about general rules, to make it clear that the performer is less important than the action. For example:

• Active voice: The landlord expects the rent check on the first of the month.
• Passive: The rent check will be collected on the first of the month.

Passive voice can also be used to make rules or expectations sound less harsh. For example:

• Active voice: Do not smoke.
• Passive voice: Smoking is prohibited.

Knowing the different uses of voice is as important in writing as in singing

The majority of your sentences should be in active voice. However, there are also effective uses of passive voice; when used sparingly, it can give particular sentences special emphasis.