Aşağıdakı hallarda biz məchul növə üstünlük veririk:

* In an active sentence we need to include the agent as subject; using a passive allows us to omit the agent by leaving out the prepositional phrase with by. Consequently, we prefer passives when the agent:

• is not known: □ My office was broken into when I was on holiday.
• is 'people in general': □ An order form can be found on page 2.
• is unimportant: □ He is thought to be somewhere in Russia.
• is obvious: □ She is being treated in hospital, (the agent is clearly 'medical staff)

* In factual writing, particularly in describing procedures or processes, we often wish to omit the agent, and use passives:

• Nuclear waste will still be radioactive even after 20,000 years, so it must be disposed of very carefully. It can be stored as a liquid in stainless-steel containers which are encased in concrete. The most dangerous nuclear waste can be turned into glass. It is planned to store this glass in deep underground mines.

* In informal contexts, particularly in conversation, we often use active sentences with a subject such as people, somebody/someone, something, they, we, or you even when we do not know who the agent is. In more formal contexts, we often prefer to use a passive so that we can avoid any mention of an agent. Compare:

• Somebody will give you the questions a week before the exam, and
• You will be given the questions a week before the exam, (or The questions will be given to you...) (both more formal)
• They're installing the new computer system next month, and
• The new computer system is being installed next month, (more formal)

Notice also that some verbs have related nouns which express the same meaning. These nouns can be used as the subject of passive sentences, with a new passive verb introduced. Compare the example above and:

• The installation of the new computer system will be completed by next month.

In English we usually prefer to put the topic (what is already being talked about) at the beginning of a sentence (or clause) and a comment on that topic at the end. Choosing the passive often allows us to do this. Compare these two texts and notice where the topic (in italics) is placed in the second sentence of each. The second text uses a passive where the emphasis is on the equipment:

• The three machines tested for the report contained different types of safety valve. The Boron Group in Germany manufactured all the equipment.
• The three machines tested for the report contained different types of safety valve. All the equipment was manufactured by the Boron Group in Germany.

It is often more natural to put long subjects at the end of a sentence. Using the passive allows us to do this. So, for example:

• I was surprised by Don's decision to give up his job and move to Sydney.
  is more natural than 'Don's decision to give up his job and move to Sydney surprised me', although the choice can depend on considerations of style and context.

Instead of making a that-clause the subject of a passive sentence, it is normal to use an it-clause:

• Everybody believed (that) the plan would fail, (active)
• It was believed that the plan would fail, (passive) is more natural than
• That the plan would fail was believed by everybody, (passive)