Passive Voice "By" Agent Exercises

In passive sentences, the person or thing that performs the action is called the agent, and it is introduced with the word "by." A key skill in using the passive voice is knowing when to include the agent and when to leave it out. Include "by + agent" when the doer is specific, famous, surprising, or provides essential information that the reader needs.

For example, "This novel was written by George Orwell" — the author is important. "The window was broken by a falling tree" — the cause is surprising and relevant. Omit the agent when it is unknown ("My phone was stolen"), obvious ("The suspect was arrested" — clearly by the police), vague ("English is spoken worldwide" — saying "by people" adds nothing), or unimportant for the message. In practice, around 80% of passive sentences in English omit the agent. Learning when to include or omit "by" makes your passive sentences sound natural and is a skill tested in Cambridge B1 Preliminary and B2 First exams, especially in sentence transformation tasks.