Passive (pass)

The correct use of the passive is still a problem for many advanced students.  It is important to know when to use the passive and how to form it.

When to use:

Use the passive when you want to emphasize what is done rather than who does it.  The action may be more important than who does it; or the doer may not be known or relevant.

    1.  The Declaration of Independence was written by Thomas
         Jefferson. 
    2.  Yesterday Noriko was stopped for speeding.
    3.  Kang's car was stolen last week.

In the first example, the document, the Declaration of Independence, is given more emphasis that the writer, Thomas Jefferson.  What you want to emphasize depends on the purpose of your paragraph:  a paragraph on the Declaration of Independence would put the focus on the document; on the other hand, a short biography of Thomas
Jefferson might use the active, "Thomas Jefferson wrote...."  The next two examples are simpler:  It doesn't matter who stopped Noriko for speeding, and we don't know who stole Kang's car, so the passive is appropriate.  Notice that we use a "by" phrase as in the first example when we want to mention the doer. 

How to form the passive:

A passive sentence is a variation on an active sentence.  The object of the active sentence becomes the subject of the passive:

    1.  Thomas Jefferson wrote the Declaration of Independence.
         (active)
    2.  The Declaration of Independence was written by Thomas
         Jefferson.  (passive)

Therefore, only verbs that can take an object (transitive verbs) can have a passive form.  Avoid mistakes like:

    3.   *An amazing thing was happened.  ("happened" can't take an
          object, so it can't be passive.)

The passive consists of a form of the verb BE followed by the past participle of the verb.  The verb BE shows the tense, whether the action is past, simple present, present perfect, etc. 

The links below are quite thorough.  You should study them carefully if I am marking passive errors in your essays.

Links: 
        Explanation and exercises:  passive
        A lot on the passive:  passive/toc.html
Advanced: http://www.grammar-quizzes.com/passivesum.html
More examples and exercises:  passive_menu.html