Active and Passive Voice

Lesson 1: Active and Passive — Understanding the Difference

Lesson: 1 of 7 | Level: 🟠 Intermediate

1. Lesson Overview

The distinction between active and passive voice is one of the most fundamental in English grammar — and one of the most misunderstood. The passive is sometimes taught as simply a way of rearranging the same information, or criticised as a weak and evasive construction to be avoided wherever possible. Neither characterisation is accurate. The passive voice is a precise and purposeful grammatical choice that serves communicative functions the active voice cannot always fulfil — and understanding when, why, and how to use it is essential for sophisticated written and spoken English.

This lesson establishes the conceptual foundation for the entire module — explaining what the passive voice is, how it differs from the active, what it does and does not change, and what principles govern the choice between the two.

Objectives

By the end of this lesson, you will be able to:

• Explain the difference between active and passive voice in grammatical terms
• Identify the agent, patient, and verb in active and passive constructions
• Understand what changes and what remains the same when a sentence is transformed from active to passive
• Explain the main reasons for choosing the passive voice over the active

2. Core Content

A. The Active Voice

In an active sentence, the grammatical subject is the agent — the person or thing that performs the action expressed by the verb. The object is the patient — the person or thing that receives or is affected by the action.

The structure of an active sentence is:

Subject (agent) + Verb + Object (patient)

For example:

Charles Darwin proposed the theory of natural selection in 1859. Scientists discovered hydrothermal vent communities on the floor of the Pacific Ocean in 1977.

In the first sentence, Charles Darwin is the agent — he performed the action of proposing. The theory of natural selection is the patient — it received the action. In the second, scientists are the agents and hydrothermal vent communities are the patient.

B. The Passive Voice

In a passive sentence, the grammatical subject is the patient — the person or thing that receives or is affected by the action. The agent — the person or thing performing the action — either moves to a by-phrase or is omitted entirely.

The structure of a passive sentence is:

Subject (patient) + Be + Past Participle (+ by + agent)

For example:

The theory of natural selection was proposed by Charles Darwin in 1859. Hydrothermal vent communities were discovered on the floor of the Pacific Ocean in 1977.

In the first sentence, the theory of natural selection — formerly the object — has become the grammatical subject. Charles Darwin — formerly the subject — has moved to a by-phrase. In the second, the agent (scientists) has been omitted entirely — it is understood and not considered important enough to name.

C. What Changes and What Does Not Change

When a sentence is transformed from active to passive, several things change — and several things remain the same.

What changes

The grammatical subject changes — the patient becomes the subject. The verb form changes — be + past participle replaces the active verb form. The agent moves — to a by-phrase, or is omitted. The focus of the sentence changes — the patient is now foregrounded.

What does not change

The essential meaning of the sentence does not change — the same action, performed by the same agent, affects the same patient. The tense does not change — the tense of be in the passive matches the tense of the active verb. The truth value does not change — the sentence describes the same event.

Consider the following pair:

Scientists are currently mapping the hydrothermal vent systems of the Indian Ocean. (active) The hydrothermal vent systems of the Indian Ocean are currently being mapped by scientists. (passive)

Both sentences describe the same ongoing activity. The tense is the same — present continuous. The event is the same — scientists mapping vent systems. What has changed is perspective and emphasis — the passive foregrounds the vent systems and places the activity of mapping in the background.

D. The By-Phrase — When to Include the Agent

The by-phrase in a passive sentence names the agent — the person or thing that performed the action. Including or omitting it is a choice governed by communicative purpose rather than grammatical necessity.

When to include the by-phrase

The agent is included when it is known, relevant, and important to the reader or listener — when naming it adds significant information.

For example:

The theory of natural selection was proposed by Charles Darwin — not by Wallace alone, as some accounts suggest. The monitoring network was established by a team of researchers from the University of Southampton.

In the first sentence, naming Darwin is important — the sentence is making a specific point about who proposed the theory. In the second, identifying the institution that established the network adds relevant information.

When to omit the by-phrase

The agent is omitted when it is unknown, unimportant, obvious from context, or deliberately withheld.

For example:

Hydrothermal vents were first observed in 1977. (who first observed them is understood — scientists on the Alvin expedition) The data has been corrupted. (who or what corrupted it may be unknown) The findings will be published next month. (by the research team — obvious from context)

In all three sentences, naming the agent would add no meaningful information. The passive allows the writer to focus on the action and its result — not on who performed it.

E. The Agent, the Patient, and the Verb

Three key terms are essential for understanding the active/passive distinction:

The agent is always the logical performer of the action — regardless of whether it appears as the grammatical subject (active) or in a by-phrase (passive) or is omitted altogether.

F. Only Transitive Verbs Can Be Made Passive

An important grammatical constraint on the passive voice is that only transitive verbs — verbs that take a direct object — can be transformed into the passive. Intransitive verbs — verbs that do not take a direct object — cannot be made passive, because there is no patient to become the subject of the passive sentence.

For example:

Darwin sailed to the Galápagos Islands. (sail is intransitive — no passive possible) The volcano erupted in 1883. (erupt is intransitive — no passive possible) Scientists discovered the vents. (discover is transitive — passive: The vents were discovered.)

Some verbs can be both transitive and intransitive — their transitive use can be made passive; their intransitive use cannot.

For example:

The glacier is melting. (intransitive — no passive) The sun is melting the glacier. (transitive — passive: The glacier is being melted by the sun.)

G. The Main Reasons for Choosing the Passive

The choice between active and passive is not arbitrary — it is governed by a set of clear communicative principles.

Reason 1 — The agent is unknown

When the agent of an action is not known, the passive allows the action to be described without specifying who performed it.

For example:

The monitoring equipment was damaged during the storm. (who or what damaged it is unknown) The data was lost during the transition to the new system. (the cause is unclear)

Reason 2 — The agent is unimportant or obvious

When the agent is unimportant to the point being made, or so obvious from context that naming it adds nothing, the passive allows the writer to focus on the action and its result.

For example:

The samples were analysed at three separate laboratories. (who analysed them — scientists — is obvious) The theory was published in 1859 and immediately attracted widespread attention. (Darwin published it — understood)

Reason 3 — The patient is more important than the agent

When the writer wants to foreground the patient — to make it the topic and the focus of the sentence — the passive places it in the subject position, where it receives the most attention.

For example:

Hydrothermal vents were discovered in 1977 — a finding that transformed our understanding of life on Earth. (the vents are the topic) The theory of natural selection was first proposed in 1859 and has been refined and confirmed by more than a century of scientific evidence. (the theory is the topic)

Reason 4 — To maintain topic continuity

In extended writing, the passive allows the writer to maintain a consistent topic — keeping the same subject across several sentences — even when the actions performed on that topic are described.

For example:

The Amazon basin is one of the most biodiverse regions on Earth. It is home to an estimated 10 per cent of all species. It has been studied by scientists for more than two centuries. It is now under serious threat from deforestation and climate change.

All four sentences have the Amazon basin as their topic — the passive in the third sentence allows this continuity to be maintained.

Reason 5 — To avoid assigning or implying responsibility

In formal, official, and diplomatic contexts, the passive can be used to describe an action without assigning responsibility — whether to avoid blame, to be tactful, or to maintain neutrality.

For example:

Mistakes were made during the initial phase of the project. (passive — responsibility not assigned) The data was misinterpreted in the original analysis. (passive — who misinterpreted it is not stated)

Reason 6 — Scientific and academic convention

In academic and scientific writing, the passive is conventionally used to describe methods, procedures, and findings — presenting them as objective, impersonal, and replicable rather than as the personal acts of individual researchers.

For example:

Samples were collected from twelve sites across the vent field and analysed at three independent laboratories. The data was processed using the standard statistical methodology described in the appendix.

Reason 7 — To achieve end focus

English places the most important information at the end of a sentence — a principle known as end focus. The passive allows writers to control what appears at the end, and therefore what receives the greatest emphasis.

For example:

Darwin proposed the theory of natural selection in 1859. (end focus on 1859) In 1859, the theory of natural selection was proposed by Darwin. (end focus on by Darwin) In 1859, the theory of natural selection was proposed. (end focus on the proposal itself)

3. Usage in Context

• The passive voice is formed with the appropriate tense of be + the past participle of the main verb — the tense of be must match the tense of the original active verb.

Scientists discovered the vents in 1977. (simple past active) The vents were discovered in 1977. (simple past passive — were matches discovered)

• Only transitive verbs can be made passive — intransitive verbs have no direct object and therefore cannot be transformed.

The volcano erupted without warning. (intransitive — no passive possible) Scientists identified the species. (transitive — passive: The species was identified by scientists.)

• The by-phrase naming the agent is included only when the agent is known, relevant, and important enough to name.

The theory was proposed by Darwin — not by Wallace, as some accounts have suggested. (agent important — included) The samples were analysed at three independent laboratories. (agent obvious — omitted)

• The passive is used when the agent is unknown — allowing the action to be described without specifying who performed it.

The monitoring equipment was damaged during the seismic event. (agent unknown) Several files appear to have been corrupted during the transfer to the new server. (agent unknown)

• The passive is used when the patient is more important than the agent — placing it in the subject position where it receives maximum attention.

Hydrothermal vents were discovered in 1977 — a finding that permanently transformed our understanding of the conditions necessary for life. The theory of continental drift was first proposed in 1912 and was dismissed by the scientific establishment for more than four decades.

• The passive maintains topic continuity in extended writing — allowing the same grammatical subject to be maintained across multiple sentences.

The Amazon basin contains approximately 10 per cent of all species on Earth. It has been studied by biologists for more than two centuries. It is currently under serious and accelerating threat from deforestation, agricultural expansion, and climate change.

• The passive is used in academic and scientific writing to describe methods, procedures, and findings in an objective and impersonal way.

Samples were collected from twelve sites across the vent field between January and March. The data was processed using the standard statistical methodology described in full in the appendix to this paper.

• The passive achieves end focus — placing the most important information at the end of the sentence where it receives the greatest emphasis.

The theory was first proposed by Darwin. (emphasis on Darwin) In 1859, the theory of natural selection was proposed. (emphasis on the proposal) The findings were published in a peer-reviewed journal last month. (emphasis on publication)

• The passive allows responsibility to be avoided or withheld — presenting an action without assigning it to a specific agent.

Errors were made in the original analysis — errors that have since been identified and corrected. The data was misinterpreted in the preliminary report, leading to conclusions that needed to be revised.

• The passive is contrasted with the active on the basis of perspective and emphasis — not on the basis of which is inherently correct or superior.

Darwin proposed the theory of natural selection. (active — Darwin is the topic; his action is foregrounded) The theory of natural selection was proposed by Darwin. (passive — the theory is the topic; Darwin’s role is backgrounded)

• In informal speech and writing, the active is generally preferred over the passive — the passive is associated with formal, academic, and official registers.

We analysed the samples at three separate laboratories. (active — informal/neutral) The samples were analysed at three separate laboratories. (passive — formal/academic)

• Do not use the passive with intransitive verbs — this is a fundamental grammatical error.

The volcano erupted without warning. (correct — intransitive; no passive) ❌ The eruption was erupted by the volcano. (incorrect — erupt is intransitive)

• When the agent is a pronoun such as someone, people, they, or everyone, omitting it in the passive is generally preferred in formal writing.

Someone has damaged the equipment. → The equipment has been damaged. (preferred in formal writing) People use plastic extensively in packaging. → Plastic is used extensively in packaging. (preferred)

4. Common Errors and Corrections

5. Lesson Mastery

After completing this lesson, you should now be able to:

    ✅ Explain the difference between active and passive voice in grammatical terms

    ✅ Identify the agent, patient, and verb in active and passive constructions

    ✅ Understand what changes and what remains the same when a sentence is transformed from active to passive

    ✅ Explain the main reasons for choosing the passive voice over the active