1. Lesson Overview
In this lesson, you will learn how agents function in passive sentences and why they are sometimes omitted.
In passive voice, the person or thing that performs the action is called the agent. The agent usually appears in a by-phrase.
Example:
The experiment was conducted by the researcher.
However, in many cases the agent is not included.
Example:
The experiment was conducted last week.
These structures are known as agentless passives.
Agentless passives are extremely common in academic writing, scientific reports, and formal communication, where the emphasis is placed on the process, result, or action rather than the person performing it.
By the end of this lesson, you will be able to:
-
explain the role of the agent in passive sentences
-
recognise when the agent is included or omitted
-
understand how agentless passives function in formal writing
-
identify situations where including the agent improves clarity
2. Concept Introduction
Consider the following sentence pair:
Active:
The technician repaired the system.
Passive with agent:
The system was repaired by the technician.
Passive without agent:
The system was repaired.
| Sentence | Focus |
|---|---|
| Active | the technician |
| Passive with agent | the system and the technician |
| Passive without agent | the system |
The passive sentence without the agent emphasises the action or result, not the person responsible.
3. Core Explanation
Passive sentences may contain an agent or may omit it entirely.
Passive with Agent
Structure:
subject + be + past participle + by + agent
Example:
The samples were analysed by the researchers.
The phrase “by the researchers” identifies the doer of the action.
Agentless Passive
Structure:
subject + be + past participle
Example:
The samples were analysed carefully.
Here the sentence focuses on the process or outcome, not the researcher.
4. Rule Table
Passive with Agent
| Structure | Example |
|---|---|
| subject + be + past participle + by + agent | The report was written by the researcher. |
Agentless Passive
| Structure | Example |
|---|---|
| subject + be + past participle | The report was written yesterday. |
Active vs Passive Focus
| Sentence | Voice | Focus |
|---|---|---|
| The researcher analysed the samples. | active | the researcher |
| The samples were analysed by the researcher. | passive with agent | the samples |
| The samples were analysed. | agentless passive | the action/result |
5. Usage
1. When the doer is unknown
Example:
The equipment was damaged during the experiment.
The person responsible is unknown or irrelevant.
2. When the doer is obvious
Example:
The suspect was arrested yesterday.
The agent is usually obvious (the police).
3. When the focus is the result
Example:
The results were published last month.
The emphasis is on the publication, not the person.
4. In scientific writing
Example:
The samples were heated to a specific temperature.
Scientific writing often avoids mentioning the researcher.
5. When the agent is important
Example:
The discovery was made by an international research team.
Here the agent is included because it provides important information.
6. Signal Words
Agentless passives often appear with expressions indicating processes or results.
| Expression | Example |
|---|---|
| yesterday | The report was submitted yesterday. |
| recently | The results were published recently. |
| during the experiment | The equipment was damaged during the experiment. |
| in the study | The data were collected in the study. |
| in the report | The conclusions were presented in the report. |
These expressions help provide context when the agent is omitted.
7. Special Cases
Passive with Non-Human Agents
Sometimes the agent is not a person, but a process or instrument.
Example:
The signal was detected by the monitoring system.
Example:
The temperature was measured by specialised equipment.
Passive with Emphasis on Discovery or Achievement
When the agent represents an important discovery or contribution, it is often included.
Example:
The theory was developed by leading physicists.
8. Additional Notes
Agentless passive sentences are especially common in:
-
scientific writing
-
research reports
-
technical manuals
-
formal descriptions of procedures
Example:
The samples were stored at low temperatures.
This style helps maintain objectivity and neutrality.
However, overusing passive voice may sometimes make writing less direct or harder to read.
9. Common Errors
⚠ Using passive unnecessarily
Incorrect:
The report was written by the researcher yesterday.
(when the focus is the researcher)
Better:
The researcher wrote the report yesterday.
Explanation:
Active voice may be clearer when the doer is important.
⚠ Missing auxiliary verb
Incorrect:
The samples analysed in the laboratory.
Correct:
The samples were analysed in the laboratory.
Explanation:
Passive voice requires a form of “be.”
⚠ Incorrect by-phrase placement
Incorrect:
By the researcher the experiment was conducted.
Correct:
The experiment was conducted by the researcher.
Explanation:
The agent normally appears at the end of the sentence.
⚠ Incorrect past participle
Incorrect:
The report was wrote by the technician.
Correct:
The report was written by the technician.
Explanation:
Passive voice requires past participle forms.
⚠ Unclear agent reference
Incorrect:
The equipment was repaired by them.
Better:
The equipment was repaired by the technician.
Explanation:
The agent should be clear and specific when included.
10. Lesson Mastery
After completing this lesson, you should now be able to:
✅ explain the role of the agent in passive sentences
✅ recognise when the agent is included or omitted
✅ understand how agentless passives function in formal writing
✅ determine when including the agent improves clarity