1. Lesson Overview
In this lesson, you will study the role of the agent in passive sentences and learn when the agent should be included or omitted.
In passive voice, the agent refers to the person or thing that performs the action. It is usually introduced by the preposition “by.”
Example:
The report was written by the researcher.
However, in many passive sentences the agent is not included, especially when it is unknown, obvious, or unimportant.
Understanding the difference between agentive passives and agentless passives helps writers control emphasis, clarity, and style, particularly in formal and academic writing.
By the end of this lesson, you will be able to:
-
recognise the agent (“by + doer”) in passive sentences
-
understand when the agent should be omitted
-
identify how agentless passives are used in formal writing
-
decide when including the agent improves clarity
2. Concept Introduction
Consider the following sentences:
The report was written by the researcher.
The report was written yesterday.
| Sentence | Agent |
|---|---|
| The report was written by the researcher. | agent included |
| The report was written yesterday. | agent omitted |
Both sentences are grammatically correct, but they emphasise different information.
The first sentence focuses on who performed the action, while the second focuses on the action itself.
3. Core Explanation
In passive sentences, the agent identifies the performer of the action and is usually introduced by “by.”
Structure:
subject + be + past participle + by + agent
Example:
The experiment was conducted by the research team.
However, the agent is often omitted when:
-
the performer is unknown
-
the performer is obvious
-
the performer is unimportant
-
the focus is on the action or result
Example:
The experiment was conducted successfully.
Here, the focus is on the result, not the performer.
4. Rule Table
Passive with Agent
| Structure | Example |
|---|---|
| subject + be + past participle + by + agent | The report was written by the scientist. |
Example:
The device was invented by an engineer.
Agentless Passive
| Structure | Example |
|---|---|
| subject + be + past participle | The report was written yesterday. |
Example:
The samples were analysed carefully.
Agent with Different Tenses
| Tense | Example |
|---|---|
| present simple | The report is written by the researcher. |
| past simple | The report was written by the researcher. |
| present perfect | The report has been written by the researcher. |
5. Usage
1. When the agent is important
Example:
The theory was developed by Albert Einstein.
The agent is important because it identifies who made the discovery.
2. When the agent is unknown
Example:
The equipment was damaged during transportation.
The performer is unknown.
3. When the agent is obvious
Example:
The suspect was arrested yesterday.
The agent (the police) is obvious and unnecessary.
4. When the focus is on the result
Example:
The samples were analysed using specialised software.
The emphasis is on the analysis process.
5. In scientific and academic writing
Example:
The results were obtained through careful experimentation.
Academic writing often prefers agentless passives to emphasise processes rather than individuals.
6. Signal Words
Certain expressions frequently appear in passive sentences describing methods or processes.
| Expression | Example |
|---|---|
| by | The report was written by the researcher. |
| using | The data were analysed using specialised software. |
| through | The results were obtained through observation. |
| during | The system was damaged during the test. |
| with | The samples were examined with advanced equipment. |
These expressions describe how the action was performed.
7. Special Cases
When Including the Agent Is Necessary
The agent should be included when it provides important information.
Example:
The discovery was made by Marie Curie.
Without the agent, the sentence would lose important historical information.
Avoiding Ambiguous Passives
Sometimes omitting the agent can make the sentence unclear.
Unclear:
The mistake was discovered.
Clearer:
The mistake was discovered by the research team.
Including the agent improves clarity and precision.
8. Additional Notes
In many formal texts, especially in scientific and technical writing, agentless passive sentences are preferred because they maintain an objective tone.
Example:
The samples were stored at low temperatures before analysis.
This style emphasises method and procedure, rather than the individual performing the action.
9. Common Errors
⚠ Using unnecessary agents
Weak:
The experiment was conducted by the team.
Better:
The team conducted the experiment.
Explanation:
Active voice is often clearer when the agent is important.
⚠ Missing agent when necessary
Unclear:
The discovery was made.
Clear:
The discovery was made by the scientist.
Explanation:
Important information may be lost without the agent.
⚠ Incorrect preposition
Incorrect:
The report was written from the researcher.
Correct:
The report was written by the researcher.
Explanation:
Passive agents use “by.”
⚠ Word order error
Incorrect:
By the researcher the report was written.
Correct:
The report was written by the researcher.
Explanation:
The agent appears after the verb phrase.
⚠ Overusing passive voice
Weak:
The experiment was conducted and the results were analysed.
Better:
The researchers conducted the experiment and analysed the results.
Explanation:
Too many passive sentences may reduce clarity and readability.
10. Lesson Mastery
After completing this lesson, you should now be able to:
✅ recognise the agent (“by + doer”) in passive sentences
✅ identify when the agent should be omitted
✅ understand how agentless passives are used in formal writing
✅ decide when including the agent improves clarity