Active-Passive Voices

What Is Active Voice?

An author may write a sentence in one of two "voices"—active or passive. The active voice emphasizes the performer (or agent) of the action:

Wind disperses plant seeds.

Smith et al. investigated the relationship.

We have analyzed the results.

The active voice is direct (performer–verb–receiver), vigorous, clear, and concise. The reader knows who is responsible for the action. 

 

What Is Passive Voice?

The passive voice, in contrast, emphasizes the receiver (or product) of the action:

Plant seeds are dispersed [by wind].

The relationship was investigated [by Smith et al].

The results have been analyzed [by us].

The passive voice is indirect (receiver–verb–performer) and can be weak, awkward, and wordy. Passive voice uses a form of the verb to be followed by a past participle (e.g., dispersed, investigated) and a by phrase. If the by phrase is omitted (the truncated passive), the reader will not directly know who or what performed the action.

When to use Passive Voice in writing?

In some sentences, passive voice can be perfectly acceptable. You might use it in the following cases:

1.The actor is unknown:

The cave paintings of Lascaux were made in the Upper Old Stone Age. [We don't know who made them.]

2.The actor is irrelevant:

An experimental solar power plant will be built in the Australian desert. [We are not interested in who is building it.]

3.You want to be vague about who is responsible:

Mistakes were made.

4.You are talking about a general truth:

Rules are made to be broken. [By whomever, whenever.]

5.You want to emphasize the person or thing acted on. For example, it may be your main topic:

Insulin was first discovered in 1921 by researchers at the University of Toronto. It is still the only treatment available for diabetes.

6.You are writing in a scientific genre that traditionally relies on passive voice. Passive voice is often preferred in lab reports and scientific research papers, most notably in the Materials and Methods section:

The sodium hydroxide was dissolved in water. This solution was then titrated with hydrochloric acid.

In these sentences you can count on your reader to know that you are the one who did the dissolving and the titrating. The passive voice places the emphasis on your experiment rather than on you.

Note: Over the past several years, there has been a movement within many science disciplines away from passive voice. Scientists often now prefer active voice in most parts of their published reports, even occasionally using the subject "we" in the Materials and Methods section.

You can find active and passive verb forms for different tenses in the following link :

http://s6.picofile.com/file/8215109150/active_passive_overview.pdf.html