The passive voice consists of a conjugated form of the verb “to be” (am, was, will be, have been, had been) and a past participle.
Passive verbs are not wrong in themselves; indeed, some contexts (a scientific paper or a laboratory report, for example) require them. Problems arise when the passive voice obscures the implied subject of the sentence (the person doing the action of the verb), when it disguises faulty or incomplete reasoning, or when it sets you up to omit a crucial piece of information.
Generally, you should not use passive verbs; they are rarely necessary in critical essays. If you find yourself resorting to passive verbs, ask yourself if you are trying to cover up lack of knowledge; if the answer is yes, then you need to rethink your point and reformulate your sentence.
Wrong: Viola is given a ring. [Because the implied subject could be either Malvolio or Olivia, I cannot determine what point you are trying to make.]
Right: Olivia gives Viola a ring.
Right: Malvolio gives Viola Olivia’s ring.
In the following example from a staging analysis, the writer’s use of the passive voice means that we lose a crucial piece of information:
When Hebe enters, she is bound to the pillar that serves as a tree.
What’s wrong in this example? We need to know WHO binds Hebe to the pillar. Which actor undertakes this action is a key piece of staging information.