Transformation and Synthesis

Lesson 4: Combining Sentences — From Simple to Complex

Lesson: 4 of 7 | Level: 🟠 Intermediate — 🟣 Upper-Intermediate

1. Lesson Overview

Sentence combining — the transformation of two or more simple sentences into a single, more complex and more informative sentence — is one of the most practically important writing skills in English. It appears in examination tasks that require the rewriting of short sentences as a single sentence using a given word. It is the foundation of all academic writing, where ideas must be expressed in precisely controlled, logically connected structures rather than in a sequence of disconnected simple sentences. And it is the skill that most directly reflects a writer’s command of the full grammatical system — because every combining strategy draws on a different area of grammar.

This lesson examines every major sentence combining strategy in detail — relative clauses, participial phrases, adverbial clauses, noun clauses, appositives, and coordination — showing how each transforms a pair of simple sentences into a single, more expressive structure.

Objectives

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

• Combine sentences using relative clauses — defining and non-defining
• Combine sentences using participial phrases — present and past
• Combine sentences using adverbial clauses — across all relationship types
• Combine sentences using noun clauses and appositives
• Choose the most appropriate combining strategy for a given pair of sentences
• Recognise and correct errors in sentence combining

2. Core Content

A. Combining with Relative Clauses

Relative clauses combine two sentences by embedding information about a noun from one sentence into another sentence as a modifier.

Step 1 — Identify the shared noun or noun phrase that appears in both sentences. Step 2 — Replace the noun in the second sentence with the appropriate relative pronoun — who, which, that, whose, where, when. Step 3 — Embed the relative clause into the first sentence immediately after the antecedent. Step 4 — Add commas if the clause is non-defining; omit commas if it is defining.

Defining relative clauses — identifying which one

The species was discovered in 1977. It has never been found elsewhere. → The species that was discovered in 1977 has never been found elsewhere.

The researcher won the international prize. She has spent forty years studying vent ecosystems. → The researcher who won the international prize has spent forty years studying vent ecosystems.

The team collected data from a site. The site had never previously been surveyed. → The team collected data from a site that had never previously been surveyed.

Non-defining relative clauses — adding information

Darwin proposed the theory of natural selection in 1859. The theory has since been confirmed by more than a century of evidence. → Darwin proposed the theory of natural selection in 1859, which has since been confirmed by more than a century of evidence.

Professor Chen received the international prize. She has spent forty years studying vent ecosystems. → Professor Chen, who has spent forty years studying vent ecosystems, received the international prize.

The 1977 expedition discovered the first hydrothermal vent community. This discovery transformed our understanding of life. → The 1977 expedition discovered the first hydrothermal vent community, which transformed our understanding of life.

Whose — possessive relative

The research team made the breakthrough. The team’s findings transformed the field. → The research team whose findings transformed the field made the breakthrough.

Where and when

The site is now protected. The vents were first observed at that site. → The site where the vents were first observed is now protected.

1977 was a remarkable year. The first hydrothermal vent community was discovered that year. → 1977, when the first hydrothermal vent community was discovered, was a remarkable year.

B. Combining with Reduced Relative Clauses

Reduced relative clauses produce a more compact and more formal structure — particularly valuable in academic writing.

Present participial reduction — active continuous

Scientists are studying the deep ocean. They face enormous challenges. → Scientists studying the deep ocean face enormous challenges.

The instruments were recording data at five-minute intervals. They transmitted it automatically. → The instruments recording data at five-minute intervals transmitted it automatically.

Past participial reduction — passive

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

The methodology was validated by three independent teams. It was accepted without question. → The methodology validated by three independent teams was accepted without question.

Infinitive reduction — first, last, only, superlative

Darwin was the first scientist. He proposed a fully developed mechanism for evolutionary change. → Darwin was the first scientist to propose a fully developed mechanism for evolutionary change.

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

C. Combining with Participial Phrases

Participial phrases combine two sentences by converting one into a non-finite clause that expresses cause, time, manner, or condition.

Present participial — simultaneous or causal

The team collected specimens from every site. They documented each one carefully. → The team collected specimens from every site, documenting each one carefully.

The researcher recognised the significance of the discovery. She immediately contacted the funding body. → Recognising the significance of the discovery, the researcher immediately contacted the funding body.

Scientists have studied vent ecosystems for fifty years. They have developed a detailed understanding of the food web. → Having studied vent ecosystems for fifty years, scientists have developed a detailed understanding of the food web.

Past participial — passive relationship

The instruments were damaged by the storm. They could not record data during the critical phase. → Damaged by the storm, the instruments could not record data during the critical phase.

The methodology was validated by three independent teams. It was accepted without question. → Validated by three independent teams, the methodology was accepted without question.

Absolute phrase — different subject

The analysis was complete. The team submitted the findings for publication. → The analysis complete, the team submitted the findings for publication.

The storm was intensifying rapidly. The expedition returned to port. → The storm intensifying rapidly, the expedition returned to port.

Critical rule — matching subjects

The subject of the participial phrase must match the subject of the main clause. If they are different, an absolute phrase must be used.

The team collected specimens. The data was remarkable. (different subjects) → The data collected by the team was remarkable. (past participial — passive) ✅ → The team collecting specimens found remarkable data. ✅ → Collecting specimens, the data was remarkable. ❌ (dangling participle)

D. Combining with Adverbial Clauses

Adverbial clauses combine two sentences by making one the main clause and converting the other into a subordinate clause that expresses the relationship between them.

Time relationships

The team completed the survey. The findings were submitted for peer review. → After the team had completed the survey, the findings were submitted for peer review. → Once the survey was complete, the findings were submitted for peer review.

The storm struck. The instruments were recording data at the time. → When the storm struck, the instruments were recording data. → The instruments were recording data when the storm struck.

Cause and reason

The equipment had failed. The team returned early. → The team returned early because the equipment had failed. → Since the equipment had failed, the team returned early.

The sample size was small. The conclusions should be treated with caution. → Given that the sample size was small, the conclusions should be treated with caution.

Condition

The safety requirements must be met. The expedition will proceed. → The expedition will proceed if the safety requirements are met. → Provided that the safety requirements are met, the expedition will proceed. → The expedition will not proceed unless the safety requirements are met.

Concession

The sample size was small. The findings were statistically significant. → Although the sample size was small, the findings were statistically significant. → The findings were statistically significant despite the small sample size. → Even though the sample size was small, the findings were significant.

Purpose

Scientists archive data. Future researchers should be able to access it. → Scientists archive data so that future researchers can access it. → Scientists archive data in order to allow future researchers to access it.

Result

The conditions were extremely extreme. The instruments could not function. → The conditions were so extreme that the instruments could not function. → The conditions were too extreme for the instruments to function.

E. Combining with Noun Clauses

Noun clauses combine two sentences by embedding one as a subject, object, or complement of the other.

As object of a reporting or mental verb

Scientists are convinced of something. The deep ocean contains many undescribed species. → Scientists are convinced that the deep ocean contains many undescribed species.

Nobody knows something. Why did the species disappear so suddenly? → Nobody knows why the species disappeared so suddenly.

The team investigated something. Was the anomaly caused by instrument error? → The team investigated whether the anomaly had been caused by instrument error.

As subject (with extraposition)

Something is remarkable. The deep ocean remains so poorly understood. → It is remarkable that the deep ocean remains so poorly understood.

Something has not been established. Whether the species can survive at greater depths. → It has not been established whether the species can survive at greater depths.

As complement

The question is something. Is the methodology adequate? → The question is whether the methodology is adequate.

F. Combining with Appositives

Appositives combine two sentences by embedding one as a noun phrase directly after a noun in the other — a compact and elegant alternative to a relative clause.

Non-restrictive appositive — supplementary information

Charles Darwin proposed the theory of natural selection. He was a 19th-century naturalist. → Charles Darwin, a 19th-century naturalist, proposed the theory of natural selection.

The Mauna Loa Observatory has recorded CO₂ data since 1958. It is the world’s longest-running atmospheric monitoring station. → The Mauna Loa Observatory, the world’s longest-running atmospheric monitoring station, has recorded CO₂ data since 1958.

Appositive vs. non-defining relative

Both the appositive and the non-defining relative clause add supplementary information — but the appositive is more compact and more formal.

Professor Chen, who is a leading authority on vent ecosystems, received the prize. (relative clause) Professor Chen, a leading authority on vent ecosystems, received the prize. (appositive — more compact)

G. Combining with Coordination

Coordination combines two sentences of equal weight using coordinating conjunctions — and, but, or, yet, so, for, nor — or semicolons with conjunctive adverbs (however, therefore, moreover, nevertheless).

And — addition

The team collected specimens. The data was sent for analysis. → The team collected specimens, and the data was sent for analysis.

But / yet — contrast

The sample size was small. The findings were significant. → The sample size was small, but the findings were significant. → The sample size was small, yet the findings were statistically significant.

So — result

The equipment failed. The team returned to port. → The equipment failed, so the team returned to port.

Semicolon + however — formal contrast

The sample size was small. The findings were statistically significant. → The sample size was small; however, the findings were statistically significant.

Semicolon + therefore — formal result

The equipment had failed. The team was forced to return to port early. → The equipment had failed; therefore, the team was forced to return to port early.

H. Choosing the Right Combining Strategy

Different combining strategies produce different emphases, different registers, and different relationships between ideas. The choice is not arbitrary — it is governed by what the writer wants to express.

3. Usage in Context

• Use defining relative clauses when the information identifies which specific person or thing is meant.

The species was discovered in 1977. It has adapted to extreme conditions. → The species that was discovered in 1977 has adapted to extreme conditions.

• Use non-defining relative clauses when the information is supplementary — the noun is already identified.

The 1977 expedition transformed our understanding of life. It was led by a team from the Woods Hole Oceanographic Institution. → The 1977 expedition, which was led by a team from the Woods Hole Oceanographic Institution, transformed our understanding of life.

• Use present participial phrases for simultaneous or causally related actions — ensuring subjects match.

The team recognised the significance of the finding. It immediately began writing up the results. → Recognising the significance of the finding, the team immediately began writing up the results.

• Use past participial phrases for passive relationships — the subject receives the action of the participle.

The methodology had been validated by three independent teams. It was accepted without further question. → Validated by three independent teams, the methodology was accepted without further question.

• Use adverbial clauses to express the precise logical relationship between two ideas — cause, condition, concession, time, purpose.

The sample size was small. The findings were still statistically significant. → Although the sample size was small, the findings were statistically significant.

• Use appositives as a compact alternative to non-defining relative clauses in formal writing.

The Mauna Loa Observatory has collected data since 1958. It is the world’s oldest CO₂ monitoring station. → The Mauna Loa Observatory, the world’s oldest CO₂ monitoring station, has collected data since 1958.

• Use noun clauses to embed the content of knowledge, belief, and uncertainty.

Scientists are not certain of something. Can the species survive at greater depths? → Scientists are not certain whether the species can survive at greater depths.

• Choose coordination when both ideas are of equal weight — and subordination when one is more important.

The sample size was small. The findings were significant. (both important) → Although the sample size was small (subordinate), the findings were significant (main). (findings more important) → The sample size was small, but the findings were significant. (equal weight)

4. Common Errors and Corrections

5. Lesson Mastery

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

    ✅ Combine sentences using relative clauses — defining and non-defining

    ✅ Combine sentences using participial phrases — present and past

    ✅ Combine sentences using adverbial clauses — across all relationship types

    ✅ Combine sentences using noun clauses and appositives

    ✅ Choose the most appropriate combining strategy for a given pair of sentences

    ✅ Recognise and correct errors in sentence combining