subject + be + past participle + by + agentUse this form when you want to say who or what performed the action.
Passive Agent
B1Use by + agent in the passive when you want to name the doer: written by Shakespeare, built by engineers. Leave it out when the doer is unknown or not important.
What you'll learn
- Add by + agent to name who did the action.
- Leave out the agent when it adds no useful information.
- Choose a person or group after by, not a tool or material.
- Use by when the doer is the important detail.
Structure
subject + be + past participleStop after the past participle when the doer is unknown, obvious, or not important.
Build a sentence
Subject
Agent
The bridgewasbuiltbyengineers
The bridge was built by engineers.
Use by before a group that performed the action.
When to use
Famous creator
Use by when the name matters: The song was written by Adele. The name is the new information.
Company or team
Name the group that did the work: The app was designed by a small team in Austin.
Result focus
Drop the doer when the result matters more: My bike was stolen last night. The key fact is the event, not the thief.
Markers
by Shakespeareby Picassoby engineersby a small teamby the company
Common mistakes
Wrong
The novel was written Jane Austen.
Correct
The novel was written by Jane Austen.
When you name the doer after a passive verb, use by before that person or group.
Wrong
The bridge was built with engineers.
Correct
The bridge was built by engineers.
Engineers are the doers of the action, so use by. With introduces a tool or instrument.
Wrong
The window was broken by a stone.
Correct
The window was broken with a stone.
A stone is a tool or cause here, not the doer. By names the actor; with names the instrument.
Wrong
The chair is made by wood.
Correct
The chair is made of wood.
Wood is the material, not the doer. Use of for material, not by.
Wrong
The thief was arrested by the police.
Correct
The thief was arrested.
By the police is possible, but often unnecessary because the doer is obvious and the result is the main point.
Common misconceptions
❝ Every passive sentence needs by + agent. ❞
No. Add by + agent only when the doer matters. Many passive sentences sound better without it.
❝ After by, I can put any noun connected to the action. ❞
After by, use the doer of the action. Tools, materials, and methods need other phrases, not by.
Skills in this rule (4)
ADD_BY_FOR_DOERw5Add by when you want to name who did the action
Use by + person or group after a passive verb when the doer matters. This answers the question Who did it?
LEAVE_OUT_AGENT_WHEN_NOT_NEEDEDw4Leave out the doer when it is unknown, obvious, or unimportant
Passive sentences do not need by + agent every time. Drop the doer when the result matters more than the person who did it.
CHOOSE_PERSON_OR_GROUP_AFTER_BYw5Use a person or group after by, not a tool or material
After by, name the doer of the action: a person, company, team, or other actor. Tools and materials go in other phrases such as with a knife or from wood.
USE_BY_WITH_NOTABLE_DOERw3Use by when the identity of the doer is important information
Add by + agent when the name carries value: an artist, writer, company, inventor, or team. The doer becomes the key detail of the message.