Sentence Structure and Clauses

Lesson 6: Reduced Relative Clauses

Lesson: 6 of 9 | Level: 🟣 Upper-Intermediate

1. Lesson Overview

A reduced relative clause is a relative clause from which the relative pronoun and the auxiliary verb — or sometimes only the relative pronoun — have been removed, leaving a non-finite or verbless construction that is more compact and more economical than its full equivalent. Reduced relative clauses are among the most characteristic features of academic and formal writing in English — they allow writers to embed complex information efficiently, avoiding the repetition of relative pronouns and auxiliary verbs while maintaining the same meaning.

Understanding how relative clauses are reduced — and when reduction is and is not possible — is one of the key skills for producing sophisticated written prose. This lesson examines every type of reduced relative clause in full — the present participial reduction, the past participial reduction, the infinitive reduction, and the verbless (adjective) reduction — with as comprehensive a treatment as possible.

Objectives

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

• Form reduced relative clauses using present participles, past participles, infinitives, and adjective phrases
• Identify the conditions under which relative clause reduction is possible
• Understand the difference between present participial and past participial reduced clauses
• Use reduced relative clauses accurately and effectively in formal and academic writing
• Recognise and correct common errors in reduced relative clause formation

2. Core Content

A. What Is a Reduced Relative Clause?

A reduced relative clause is formed by removing the relative pronoun and the auxiliary verb from a full relative clause, and — where necessary — changing the main verb to a non-finite form.

Compare the following:

In each case, the reduced version is more compact — it carries the same information in fewer words, with a more formal and more economical style.

B. Type 1 — Present Participial Reduction

A full relative clause containing an active verb in a continuous form can be reduced by removing the relative pronoun and the auxiliary be, leaving the present participle (-ing form).

Condition for present participial reduction

The relative pronoun must be the subject of the relative clause. The relative clause must contain a continuous verb form — be + present participle.

Formation

Full clause: relative pronoun + be + present participle → Reduced: present participle alone

For example:

Scientists who are mapping the ocean floor use autonomous vehicles. → Scientists mapping the ocean floor use autonomous vehicles.

The instruments that are recording the data transmit it automatically. → The instruments recording the data transmit it automatically.

The team that was collecting samples encountered an unexpected storm. → The team collecting samples encountered an unexpected storm.

Note that present participial reduction works for both defining and non-defining relative clauses — though when reducing non-defining clauses, the commas are retained.

Professor Chen, who is studying vent ecosystems, received the prize. → Professor Chen, studying vent ecosystems, received the prize.

C. Type 2 — Past Participial Reduction

A full relative clause containing a passive verb can be reduced by removing the relative pronoun and the auxiliary be, leaving the past participle.

Condition for past participial reduction

The relative pronoun must be the subject of the relative clause. The relative clause must contain a passive verb form — be + past participle.

Formation

Full clause: relative pronoun + be + past participle → Reduced: past participle alone

For example:

The species that was discovered in 1977 is unique. → The species discovered in 1977 is unique.

The data that was collected during the expedition filled several terabytes. → The data collected during the expedition filled several terabytes.

The vent community, which was first observed in 1977, transformed our understanding of life. → The vent community, first observed in 1977, transformed our understanding of life.

The methodology that was described in the previous section will be applied throughout. → The methodology described in the previous section will be applied throughout.

Past participial reduced clauses are particularly common in academic writing — they appear constantly in scientific papers, reports, and formal documents.

D. Type 3 — Reduction with Simple Present and Simple Past

Less commonly, a full relative clause with a simple active verb — not a continuous form — can be reduced using the present participle. This is possible when the relative clause describes an ongoing or habitual action.

Formation

Full clause: relative pronoun + simple present/past active verb → Reduced: present participle

For example:

The team that manages the monitoring network operates from Southampton. → The team managing the monitoring network operates from Southampton.

Scientists who work at extreme depths face unique physiological challenges. → Scientists working at extreme depths face unique physiological challenges.

Organisms that live in hydrothermal vent ecosystems have evolved remarkable adaptations. → Organisms living in hydrothermal vent ecosystems have evolved remarkable adaptations.

This type of reduction is extremely common and is one of the most important features of academic prose — the -ing participial phrase is used pervasively to modify nouns in formal English.

E. Type 4 — Infinitive Reduction

A full relative clause can sometimes be reduced to an infinitive phrase — particularly when the relative clause expresses purpose, possibility, or the first/last/only status of the antecedent.

Condition for infinitive reduction

Infinitive reduction is appropriate when the relative clause expresses:

• Purpose — the antecedent is intended for a specific purpose
• Possibility — the antecedent can perform a specific action
• Superlative or unique status — first, last, only, next, etc.

Formation

Full clause: relative pronoun + modal verb + bare infinitive → Reduced: to-infinitive

For example:

The team that will conduct the survey departs next week. → The team to conduct the survey departs next week.

The first scientist who reached the floor of the trench made extraordinary observations. → The first scientist to reach the floor of the trench made extraordinary observations.

The only instrument that could detect the anomaly was deployed during the final dive. → The only instrument to detect the anomaly was deployed during the final dive.

Scientists are looking for a method that can map the vent field more efficiently. → Scientists are looking for a method to map the vent field more efficiently.

The last team that surveyed this site did so in 2009. → The last team to survey this site did so in 2009.

Infinitive reduction is also used after superlatives:

It was the most significant discovery that had ever been made in deep-sea biology. → It was the most significant discovery ever made in deep-sea biology.

F. Type 5 — Verbless (Adjective Phrase) Reduction

A relative clause containing be + adjective or be + noun phrase as a complement can be reduced to just the adjective phrase or noun phrase — a verbless reduction.

Condition for verbless reduction

The relative clause must contain be + adjective/noun complement. The reduced adjective phrase must follow the noun it modifies.

Formation

Full clause: relative pronoun + be + adjective/noun phrase → Reduced: adjective/noun phrase after noun

For example:

The discovery, which was extraordinary, transformed the field. → The discovery, extraordinary in its implications, transformed the field.

A proposal that is inadequate in its methodology will be rejected. → A proposal inadequate in its methodology will be rejected.

Organisms that are unique to hydrothermal vent ecosystems have attracted intense scientific interest. → Organisms unique to hydrothermal vent ecosystems have attracted intense scientific interest.

The vent community, which is notable for its extraordinary diversity, was first observed in 1977. → The vent community, notable for its extraordinary diversity, was first observed in 1977.

Verbless reduced clauses are particularly common with adjectives that are typically postpositive — placed after the noun rather than before it.

G. When Reduction Is Not Possible

Not all relative clauses can be reduced. Reduction is not possible in the following circumstances.

1. When the relative pronoun is the object

When the relative pronoun is the object of the relative clause — not the subject — reduction to a participial phrase is not possible in the standard way. These clauses are typically either left in full form or converted using other structures.

The data that the team collected was remarkable. (object — that = object of collected) → The data collected by the team was remarkable. (passive participial — possible if agent included)

2. When the relative clause has a different subject from the main clause

If the relative clause has a different subject from the main clause, reduction creates an ambiguity about who or what is performing the action. In such cases, reduction should be avoided.

The equipment which the team had designed failed during the dive. → The equipment designed by the team failed during the dive. (acceptable with passive participial) → The equipment designing the system failed. ❌ (reduction to active participle — impossible; equipment does not design)

3. When the relative clause is non-defining with a personal pronoun subject

Non-defining clauses referring to a specific named person or place are usually not reduced if this would create an awkward or ambiguous structure.

Darwin, who proposed the theory, changed science forever. (natural — full clause) Darwin, proposing the theory, changed science forever. (reduced — possible but implies a specific moment)

4. When the relative clause contains a stative verb

Relative clauses with stative verbs — know, believe, contain, belong, consist — typically cannot be reduced to participial form because stative verbs do not normally take continuous forms.

The ocean that contains the most biodiversity is the Pacific. (stative — no participial reduction) → The ocean containing the most biodiversity is the Pacific. ✅ (dynamic reading — acceptable in academic writing)

Note that in academic prose, containing, comprising, and consisting of are widely used as reduced relative clauses even though contain, comprise, and consist are technically stative.

H. Distinguishing Present and Past Participial Reduced Clauses

One of the most important distinctions in reduced relative clauses is between present participial and past participial forms — the choice depends on whether the original relative clause was active or passive.

The contrast is critical — studying implies an active agent; studied implies a passive recipient.

A species studying the ecosystem would be a species that actively studies — an impossible meaning. A species studied by scientists is a species that is the object of scientific study — a natural meaning.

3. Usage in Context

• Use present participial reduced clauses to describe the ongoing activity of the antecedent — replacing who/which is/are + -ing.

Scientists mapping the ocean floor using autonomous vehicles have identified hundreds of previously unknown vent fields. Organisms living in hydrothermal vent ecosystems have evolved extraordinary adaptations to conditions of extreme pressure, heat, and chemical toxicity.

• Use past participial reduced clauses to describe what has been done to the antecedent — replacing which was/were + past participle.

The data collected during the six-month expedition has been archived in full for use by future research teams. The methodology described in the previous section will be applied to all subsequent phases of the survey.

• Use present participial reduced clauses to replace who/which + simple present active verb in academic writing — one of the most common and most important formal prose patterns.

Researchers studying the relationship between ocean temperature and coral bleaching have documented a dramatic increase in bleaching frequency over the past two decades. Species inhabiting the hadal zone — the deepest region of the ocean — experience some of the most extreme conditions on Earth.

• Use past participial reduced clauses to express a passive relationship economically — particularly in academic and scientific writing.

The species, first observed in 1977, has since been found at more than twenty vent sites across the Pacific. The vent community, now recognised as one of the most biodiverse ecosystems on the planet, was initially dismissed as a scientific curiosity.

• Use infinitive reduced clauses after first, last, only, next, and superlatives.

Darwin was the first scientist to propose a fully developed mechanism for evolutionary change. The 1977 expedition was the first to observe a living hydrothermal vent community. It is the most significant discovery in deep-sea biology ever made.

• Use infinitive reduced clauses to express purpose — after nouns indicating something intended for a specific use.

Scientists are developing new instruments to detect changes in ocean chemistry at greater precision than has previously been possible. The team is looking for a sampling strategy to capture the full range of species present at the site.

• Use verbless reduced clauses to add compact, post-nominal modification — particularly with adjectives that follow nouns.

Organisms unique to hydrothermal vent ecosystems provide some of the most compelling evidence for chemosynthesis-based food webs. The vent field, remarkable for its extent and biological diversity, was first documented during the 2004 expedition.

• Distinguish present participial from past participial reduced clauses precisely — active agency vs. passive reception.

The team conducting the survey (= the team that is conducting) — active; the team is doing the conducting The survey conducted by the team (= the survey that was conducted) — passive; the survey is being conducted

• In academic writing, chain reduced relative clauses to produce economical, information-dense prose.

The data, collected over eighteen months and processed using the methodology described in Section 3, provides the most comprehensive baseline record of conditions at the site ever assembled.

• Be alert to the dangling participle error — when the reduced clause does not clearly attach to the correct antecedent.

Studying the vent field, the instruments revealed extraordinary data. ❌ (the instruments do not study — the scientists do) Studying the vent field, the scientists recorded extraordinary data with their instruments. ✅

4. Common Errors and Corrections

5. Lesson Mastery

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

    ✅ Form reduced relative clauses using present participles, past participles, infinitives, and adjective phrases

    ✅ Identify the conditions under which relative clause reduction is possible

    ✅ Understand the difference between present participial and past participial reduced clauses

    ✅ Use reduced relative clauses accurately and effectively in formal and academic writing

    ✅ Recognise and correct common errors in reduced relative clause formation