The Sentence
Lesson 6: Phrases and Clauses
Lesson: 6 of 9 | Level: 🔵 Beginner
1. Lesson Overview
Every sentence in English is built from smaller units of meaning. Some of those units have a subject and a finite verb; others do not. Those that do are called clauses; those that do not are called phrases. Both are essential building blocks of English sentences, and understanding the difference between them — and the different types of each — is fundamental to analysing and constructing sentences with confidence and precision.
This lesson examines phrases and clauses in detail. It builds directly on the sentence structure work of Lesson 4 and prepares the ground for the more advanced clause work that appears in Module 8 — Sentence Structure and Clauses.
Objectives
By the end of this lesson, you will be able to:
- Define a phrase and identify the main types of phrases in English
- Define a clause and distinguish between independent and dependent clauses
- Identify the main types of dependent clauses
- Recognise and correct common errors involving phrases and clauses
2. Core Content
A. The Distinction Between a Phrase and a Clause
The single most important distinction in this lesson is the one between a phrase and a clause.
A phrase is a group of words that functions as a single unit within a sentence but does not contain both a subject and a finite verb. A clause is a group of words that contains both a subject and a finite verb.
| Unit | Contains Subject + Finite Verb? | Example |
|---|---|---|
| Phrase | No | the surface of the moon / running along the fault line / extremely cold |
| Clause | Yes | the surface of the moon is barren / the glacier retreats every summer |
Consider the following sentences:
The surface of the moon is barren and heavily cratered. Running along the fault line for hundreds of kilometres, the crack is clearly visible from the air.
In the first sentence, the surface of the moon is a phrase — it has no finite verb. The surface of the moon is barren and heavily cratered is a clause — it has both a subject and a finite verb. In the second, running along the fault line for hundreds of kilometres is a phrase; the crack is clearly visible from the air is a clause.
B. Types of Phrases
English recognises several types of phrases, each named after its most important word — its head word.
Noun phrases
A noun phrase consists of a noun and all the words that modify it — determiners, adjectives, prepositional phrases, and relative clauses. It functions as a subject, object, or complement within a sentence.
For example:
The deepest point on Earth lies in the Mariana Trench in the western Pacific Ocean. An extraordinary diversity of life has been discovered in hydrothermal vent ecosystems.
In the first sentence, the deepest point on Earth is a noun phrase functioning as the subject. In the second, an extraordinary diversity of life is a noun phrase functioning as the subject, and hydrothermal vent ecosystems is a noun phrase functioning as the object of a preposition.
Verb phrases
A verb phrase consists of a main verb and any auxiliary verbs that accompany it. It forms the predicate of the sentence or clause.
| Verb Phrase | Example |
|---|---|
| is melting | The Arctic sea ice is melting at an accelerating rate. |
| has been discovered | A new species of deep-sea fish has been discovered near the Mariana Trench. |
| will have completed | The team will have completed the survey by the end of the month. |
| should be monitored | Volcanic activity should be monitored continuously. |
Adjective phrases
An adjective phrase consists of an adjective and any words that modify it — typically adverbs of degree. It modifies a noun or pronoun.
For example:
The Sahara is extraordinarily vast, covering approximately 9.2 million square kilometres. Antarctica is far colder than any other continent on Earth.
In the first sentence, extraordinarily vast is an adjective phrase — extraordinarily modifies the adjective vast. In the second, far colder than any other continent on Earth is an adjective phrase modifying Antarctica.
Adverb phrases
An adverb phrase consists of an adverb and any words that modify it. It modifies a verb, an adjective, or another adverb.
For example:
The tectonic plates move extremely slowly beneath the Earth’s surface. Temperatures in the deep ocean remain remarkably constant throughout the year.
In the first sentence, extremely slowly is an adverb phrase — extremely modifies the adverb slowly. In the second, remarkably constant is an adjective phrase, and throughout the year is a prepositional phrase functioning as an adverb phrase.
Prepositional phrases
A prepositional phrase consists of a preposition and its object — a noun, pronoun, or noun phrase. It functions as an adjective or adverb within a sentence.
For example:
The summit of Mount Everest rises 8,849 metres above sea level. Beneath the surface of the Antarctic ice sheet, liquid lakes have been discovered.
In the first sentence, of Mount Everest is a prepositional phrase functioning as an adjective — it modifies summit. Above sea level is a prepositional phrase functioning as an adverb — it modifies rises. In the second, beneath the surface of the Antarctic ice sheet is a prepositional phrase functioning as an adverb — it tells us where the lakes were discovered.
Participial phrases
A participial phrase begins with a present participle (-ing form) or a past participle (-ed or irregular form) and functions as an adjective within a sentence, modifying a noun or pronoun.
For example:
Flowing eastward through nine countries, the Amazon finally empties into the Atlantic Ocean. Discovered in 1977, hydrothermal vents support ecosystems that receive no sunlight whatsoever.
In the first sentence, flowing eastward through nine countries is a participial phrase modifying the Amazon. In the second, discovered in 1977 is a participial phrase modifying hydrothermal vents. Both phrases must be placed as close as possible to the noun they modify — failing to do so produces a dangling participle, an error explored in Lesson 7.
Infinitive phrases
An infinitive phrase consists of a to-infinitive and any words that follow it. It can function as a noun, adjective, or adverb within a sentence.
For example:
To understand the effects of climate change, scientists study ice cores from Antarctica. The first team to reach the summit of Everest included Edmund Hillary and Tenzing Norgay.
In the first sentence, to understand the effects of climate change is an infinitive phrase functioning as an adverb — it tells us why scientists study ice cores. In the second, to reach the summit of Everest is an infinitive phrase functioning as an adjective — it modifies team.
C. Types of Clauses
As introduced in Lesson 4, there are two fundamental types of clause — independent and dependent. Dependent clauses can be further divided into three subtypes.
Independent clauses
An independent clause contains a subject and a finite verb and expresses a complete thought. It can stand alone as a sentence.
For example:
The Amazon is the world’s largest river by discharge. Scientists have not yet explored the full extent of the deep ocean.
Both are independent clauses — each is complete, self-contained, and capable of standing alone.
Dependent clauses
A dependent clause contains a subject and a finite verb but cannot stand alone because it is introduced by a subordinating conjunction or a relative pronoun that makes it depend on a main clause.
There are three types of dependent clause.
Adverbial clauses
An adverbial clause is introduced by a subordinating conjunction and functions as an adverb — it modifies the verb of the main clause by expressing time, reason, contrast, condition, purpose, or result.
| Relationship | Conjunction | Example |
|---|---|---|
| Time | when, while, after, before, since, until | When tectonic plates collide, mountain ranges are formed. |
| Reason | because, since, as | Because the permafrost is thawing, methane is being released. |
| Contrast | although, even though, whereas | Although Antarctica is a desert, it contains vast quantities of fresh water. |
| Condition | if, unless, provided that | Unless carbon emissions are reduced, temperatures will continue to rise. |
| Purpose | so that, in order that | Scientists monitor volcanoes so that eruptions can be predicted. |
Relative clauses
A relative clause is introduced by a relative pronoun — who, whom, whose, which, or that — and functions as an adjective, modifying a noun or pronoun in the main clause.
For example:
The scientist who discovered the structure of DNA worked at King’s College London. The Amazon basin, which covers approximately 40 per cent of South America, is the world’s largest tropical rainforest.
In the first sentence, who discovered the structure of DNA is a relative clause identifying which scientist is meant — it is a defining relative clause. In the second, which covers approximately 40 per cent of South America is a relative clause adding extra information about the Amazon basin — it is a non-defining relative clause, set off by commas.
Noun clauses
A noun clause functions as a noun within the sentence — as a subject, object, or complement. It is typically introduced by that, whether, if, or a wh- word.
For example:
Scientists believe that the universe is approximately 13.8 billion years old. Whether life exists elsewhere in the universe remains one of the greatest unanswered questions in science.
In the first sentence, that the universe is approximately 13.8 billion years old is a noun clause functioning as the object of the verb believe. In the second, whether life exists elsewhere in the universe is a noun clause functioning as the subject of the sentence.
3. Usage in Context
| Rule | Example |
|---|---|
| A phrase does not contain a subject and a finite verb; a clause does. | The surface of the moon (phrase) / The surface of the moon is barren (clause) |
| A noun phrase can function as a subject, object, or complement. | The discovery of penicillin transformed modern medicine. |
| A verb phrase forms the predicate of a sentence or clause. | Scientists have been studying the effects of climate change for decades. |
| A prepositional phrase can function as an adjective or an adverb. | The rings of Saturn (adjective) / The spacecraft orbited above the clouds (adverb) |
| A participial phrase must be placed immediately before or after the noun it modifies. | Flowing through nine countries, the Amazon empties into the Atlantic. |
| A dangling participle occurs when a participial phrase does not clearly modify the intended noun. | ❌ Flying over the Amazon, the river appeared vast. ✅ Flying over the Amazon, the pilot noticed how vast the river appeared. |
| An adverbial clause at the start of a sentence is followed by a comma. | Because the glacier retreated, sea levels rose. |
| An adverbial clause at the end of a sentence does not require a comma. | Sea levels rose because the glacier retreated. |
| A defining relative clause identifies which noun is meant and is not set off by commas. | The country that produces the most coffee in the world is Brazil. |
| A non-defining relative clause adds extra information and is set off by commas. | Brazil, which is the world’s largest coffee producer, is also home to the Amazon rainforest. |
| Use who for people and which for things in relative clauses. | The scientist who mapped the human genome / The telescope which mapped the Milky Way |
| A noun clause introduced by that can often omit that in informal contexts. | Scientists believe the universe is 13.8 billion years old. |
| Do not use a comma before that in a defining relative clause or noun clause. | Scientists believe that the universe is 13.8 billion years old. (no comma before that) |
| An independent clause can stand alone; a dependent clause cannot. | ❌ Although the data was incomplete. ✅ Although the data was incomplete, the team published their findings. |
| Infinitive phrases expressing purpose can be introduced by in order to in formal writing. | In order to understand the effects of ocean acidification, scientists monitor pH levels continuously. |
| Avoid stringing too many phrases together without a finite verb — the result is a sentence fragment. | ❌ A remarkable discovery in the deep ocean near the Mariana Trench. ✅ A remarkable discovery was made in the deep ocean near the Mariana Trench. |
4. Common Errors and Corrections
| Error ❌ | Correction ✅ | Explanation |
|---|---|---|
| Running along the fault line for hundreds of kilometres. | The crack runs along the fault line for hundreds of kilometres. | A participial phrase without a subject or finite verb is a sentence fragment. |
| The scientist which discovered penicillin was Alexander Fleming. | The scientist who discovered penicillin was Alexander Fleming. | Who — not which — is used in relative clauses referring to people. |
| Although the data was incomplete, but the team published their findings. | Although the data was incomplete, the team published their findings. | Although and but cannot both introduce the same contrast; one conjunction is sufficient. |
| Scientists believe that the universe it is 13.8 billion years old. | Scientists believe that the universe is 13.8 billion years old. | The subject of the noun clause — the universe — cannot be restated as a pronoun within the same clause. |
| The Amazon, that is the world’s largest river by discharge, flows through Brazil. | The Amazon, which is the world’s largest river by discharge, flows through Brazil. | In a non-defining relative clause, use which — not that. |
| Flying over the Amazon, the river appeared vast and brown. | Flying over the Amazon, the pilot noticed how vast and brown the river appeared. | A participial phrase must clearly modify the subject of the main clause — here, the pilot, not the river, was flying. |
| The discovery of new species in the deep ocean are exciting scientists worldwide. | The discovery of new species in the deep ocean is exciting scientists worldwide. | The subject is discovery — singular — not species or ocean. |
| Scientists study ice cores for to understand past climates. | Scientists study ice cores to understand past climates. | The to-infinitive of purpose does not require for before it. |
| The team completed the survey, they published their findings the following month. | The team completed the survey and published their findings the following month. | Two independent clauses cannot be joined by a comma alone — this is a comma splice. |
| Whether does life exist on Mars remains an open question. | Whether life exists on Mars remains an open question. | A noun clause introduced by whether uses standard word order — subject + verb — not inverted word order. |
5. Lesson Mastery
After completing this lesson, you should now be able to:
✅ Define a phrase and identify the main types of phrases in English
✅ Define a clause and distinguish between independent and dependent clauses
✅ Identify the main types of dependent clauses
✅ Recognise and correct common errors involving phrases and clauses