A sentence is a grammatical unit that typically contains at least one independent clause and can express a statement, question, command, or exclamation.
In written English, sentences usually begin with a capital letter and end with a period (full stop), question mark, or exclamation mark.
Here are four examples:
- The last train leaves at midnight. — A statement
- Has anyone seen my keys? — A question
- Keep the entrance clear. — An instruction
- What a wonderful surprise! — An exclamation
Each sentence communicates something complete, but they do so in different ways. A sentence might be as short as Come in. or contain several clauses that connect ideas.
Length isn’t what makes a sentence complete. Its grammatical structure matters more.
What Makes a Complete Sentence?
Most complete English sentences contain a subject and a verb. The subject generally identifies who or what the clause is about, while the verb expresses an action, event, or state.
The delivery arrived before sunset.
Here, the delivery is the subject, and arrived is the verb. The clause can stand on its own without needing another clause to complete it.
But the presence of a subject and verb doesn’t always guarantee a complete sentence.
An Independent Clause Makes the Difference
Compare:
The caretaker returned before sunset.
When the caretaker returned before sunset.
The first is a complete sentence. The second contains the same subject and verb, but when introduces a dependent clause. In this construction, the reader is left expecting something more.
Adding an independent clause completes it:
When the caretaker returned before sunset, the front gate was still open.
A group of words may also be a phrase rather than a clause.
Behind the locked door.
This prepositional phrase tells us about a location, but it doesn’t contain a subject and predicate forming an independent clause.
It can become part of a sentence:
Behind the locked door, someone was playing the piano.
The distinction is useful when checking your own writing. A group of words may convey recognizable information without forming a grammatically complete sentence.
Some Verbs Need Additional Information
Finding a subject and verb is only part of the picture. Certain verbs require other elements to complete their grammatical structure.
For example:
The receptionist put the parcel.
This sounds unfinished because put, when it means placing something somewhere, normally requires both an object and a location or destination.
The receptionist put the parcel on the counter.
Now the verb has the information it requires.
Compare that with:
The receptionist smiled.
Nothing is missing. Smiled can function without an object or location.
The point is not that sentences need extra details to sound interesting. Some verbs require particular elements, while others are complete without them.
Short Responses in Conversation
Everyday English also includes responses such as:
Absolutely!
No problem.
Of course.
These expressions can function as complete responses in conversation even though they don’t have the structure of full independent clauses.
They’re perfectly natural in the right context. For identifying complete sentences in ordinary formal writing, however, an independent clause remains the most useful starting point.
Parts of a Sentence
The two main parts traditionally identified in a sentence are the subject and the predicate.
The subject generally identifies who or what the clause is about. The predicate contains the verb and says something about the subject.
Consider:
The technician replaced the damaged cable before noon.
| Sentence part | Words | Function |
|---|---|---|
| Complete subject | The technician | Identifies who performed the action |
| Complete predicate | replaced the damaged cable before noon | Tells us what the subject did |
| Verb | replaced | Expresses the action |
| Direct object | the damaged cable | Identifies what was replaced |
| Time expression | before noon | Indicates when the replacement happened |
The predicate includes more than the verb. In this example, it also contains the direct object and a time expression.
A subject can be longer than a single noun:
The books on the top shelf belong to my grandfather.
The complete subject is the books on the top shelf, not simply books.
The main verb, belong, agrees with the plural head noun books.
Objects and Complements
What follows a verb depends partly on the kind of verb being used.
Priya repaired the broken drawer.
The broken drawer is the direct object of repaired. It identifies what Priya repaired.
Now compare:
The repaired drawer looks uneven.
Here, uneven is a subject complement. It describes the repaired drawer through the linking verb looks. It isn’t an object receiving an action.
An object complement provides information about an object:
The committee appointed Elena chairperson.
Elena is the direct object, while chairperson identifies the position assigned to her.
These distinctions explain why the words following a verb aren’t necessarily all objects.
Four Types of Sentences by Function
English sentences are commonly grouped into four types according to their grammatical form and the purpose they typically serve: declarative, interrogative, imperative, and exclamatory.
| Type | Typical purpose | Example |
|---|---|---|
| Declarative | Makes a statement | The new timetable starts on Monday. |
| Interrogative | Asks a question | Has the new timetable been approved? |
| Imperative | Gives an instruction or makes a request | Please send me the new timetable. |
| Exclamatory | Expresses a strong reaction | What an unexpected announcement that was! |
Declarative Sentences
Statements are the most familiar kind of sentence in everyday writing. A declarative sentence presents information, describes something, or makes a claim.
The museum has extended its opening hours.
A negative statement is still declarative:
The museum will not open on public holidays.
Declarative sentences normally end with a period (full stop), although an exclamation mark can sometimes convey strong emotion.
Interrogative Sentences
Questions such as these have interrogative form:
Why did the delivery arrive so late?
Is the exhibition open on Sundays?
In many English questions, an auxiliary verb appears before the subject. But that pattern doesn’t apply to every interrogative.
Who approved the final design?
Here, who is the subject, so there is no need for the usual auxiliary-before-subject arrangement.
An interrogative doesn’t always seek information. Someone asking:
Could you move your bag?
is usually making a polite request rather than asking whether the listener possesses the ability to move it.
Imperative Sentences
Instructions, requests, advice, and commands often use imperative sentences.
Save a copy of the document before editing it.
Please take a seat near the front.
The subject of an imperative is generally understood to be you, even when it isn’t written. That’s why Save a copy is a complete sentence rather than a fragment.
Imperatives can also be negative:
Don’t leave your bicycle near the emergency exit.
An imperative doesn’t have to sound forceful. Please come in and Leave immediately share the same broad grammatical form, but their tone and purpose differ.
Exclamatory Sentences
Exclamatory constructions express reactions such as surprise, admiration, or excitement. They often begin with what or how.
What a difference the renovation has made!
How beautifully the choir performed!
An exclamation mark can also add emotion to other sentence forms.
We finally reached the summit!
This has declarative structure, although the punctuation conveys excitement.
Watch out!
This is an imperative expressing urgency.
In other words, the punctuation and emotional force of a sentence don’t always determine its grammatical type.
Four Types of Sentences by Structure
Sentence structure concerns how clauses are arranged.
An independent clause can stand alone as a complete sentence. A dependent clause forms part of a larger construction and cannot normally stand alone as a complete sentence in standard written English.
The four commonly taught structures are simple, compound, complex, and compound-complex.
1. Simple Sentence
A simple sentence has one independent clause.
Before the guests arrived, Daniel checked the seating plan.
At first glance, the opening words might make this look complex. But before the guests arrived is a dependent clause, so this example is actually a complex sentence, not a simple one.
Compare the genuinely simple version:
Before dinner, Daniel checked the seating plan.
Before dinner is a prepositional phrase, not a clause. The sentence therefore contains just one independent clause.
A simple sentence can also describe more than one action:
Daniel checked the seating plan and rearranged three chairs.
The two verb phrases share the subject Daniel. This is a simple sentence with a compound predicate, not a compound sentence.
2. Compound Sentence
A compound sentence contains at least two independent clauses.
The bakery had sold out of bread, but the café next door still had sandwiches.
Both clauses could stand alone:
- The bakery had sold out of bread.
- The café next door still had sandwiches.
The coordinating conjunction but connects them and signals a contrast.
A semicolon can also join closely related independent clauses:
The first offer expired yesterday; the second remains available.
3. Complex Sentence
A complex sentence contains one independent clause and at least one dependent clause.
Although the road was flooded, the morning bus arrived on time.
The opening clause introduces a circumstance that makes the result noteworthy. The main clause, the morning bus arrived on time, can stand alone.
Dependent clauses can also appear within the main clause:
The woman who found the missing wallet handed it to the station attendant.
Who found the missing wallet is a relative clause identifying the woman.
4. Compound-Complex Sentence
A compound-complex sentence combines at least two independent clauses with at least one dependent clause.
When the power returned, the shop reopened, and customers began coming inside.
When the power returned is dependent.
The shop reopened and customers began coming inside are independent clauses joined by and.
Comparing the Four Structures
The same general situation can be presented using different clause arrangements.
| Structure | Example |
|---|---|
| Simple | The library reopened after extensive repairs. |
| Compound | The library reopened, and visitors filled the reading rooms. |
| Complex | After the repairs were completed, the library reopened. |
| Compound-complex | After the repairs were completed, the library reopened, and visitors returned to the reading rooms. |
A sentence doesn’t become better merely because it has more clauses. The structure should suit the information and the relationship between the ideas.
How to Tell Whether a Group of Words Is a Sentence
Some incomplete constructions are easy to recognize. Others contain verbs or several descriptive details and may look complete at first.
Rather than counting words or looking only for punctuation, check whether the group contains an independent main clause. The subject may be understood, as in an imperative, and the verb may require an object or complement.
The following examples show how these distinctions work.
| Example | Classification | Why |
|---|---|---|
| The documents waiting near reception. | Fragment | This is a noun phrase. Waiting near reception describes the documents, but there’s no independent main clause. |
| Check the address before submitting the form. | Complete sentence | This is an imperative. Its subject, you, is understood. |
| Although the meeting finished early. | Fragment | Although introduces a dependent clause without an independent main clause. |
| The designers reviewed the plans and approved the changes. | Complete simple sentence | Two coordinated verb phrases share one subject within a single independent clause. |
| The designers reviewed the plans, and the client approved the changes. | Complete compound sentence | Two independent clauses are joined by and. |
| The parcel was placed on the shelf. | Complete sentence | The passive verb construction has the required information, including the location. |
The fourth and fifth examples are particularly easy to confuse. Both describe two actions, but only the fifth contains two independent clauses.
There’s another useful clue in the first example: waiting looks like a verb, but here it belongs to a participial clause modifying documents. It doesn’t supply the independent main clause needed for a complete sentence.
That is why spotting a verb-like word is not a reliable test on its own.
Sentence Fragments, Run-ons, and Comma Splices
A sentence fragment lacks a complete independent main clause. Run-ons and comma splices present a different problem: they involve independent clauses that haven’t been connected correctly.
Sentence Fragments
Suppose someone writes:
The painting beside the staircase.
As a standalone sentence in ordinary formal prose, this is incomplete. Adding a predicate turns it into a full clause:
The painting beside the staircase belongs to a private collector.
Sometimes a fragment needs to be attached to another sentence rather than expanded on its own.
For example:
We cancelled the picnic. Because the weather forecast changed.
A smoother correction is:
We cancelled the picnic because the weather forecast changed.
Not every fragment is a mistake in context. Fiction, conversation, headlines, and informal writing regularly use fragments deliberately for rhythm or emphasis.
Run-on Sentences
A run-on sentence improperly joins independent clauses.
In a fused sentence, the clauses appear without the punctuation or grammatical connection needed to separate or join them.
Incorrect:
The application deadline passed several candidates requested an extension.
Corrected:
The application deadline passed, but several candidates requested an extension.
The correction keeps the two related ideas together while making the clause boundary clear.
A run-on isn’t simply a long sentence. Even a brief sentence can contain this error if its clauses are joined improperly.
Comma Splices
A comma splice occurs when two independent clauses are joined with only a comma, in a construction normally considered incorrect in standard formal writing.
Incorrect:
The hotel was fully booked, we reserved a room nearby.
Corrected:
The hotel was fully booked, so we reserved a room nearby.
A semicolon offers another option:
The hotel was fully booked; we reserved a room nearby.
The clauses could also be written as two separate sentences.
A comma splice is commonly treated as a type of run-on error, although the terms are sometimes used differently in teaching materials. The practical issue is the same: the relationship between the independent clauses needs appropriate punctuation or grammatical linking.
How Sentence Structure Changes Meaning and Emphasis
Two sentences can be grammatically correct yet leave their relationship unclear.
The inspection was delayed. The laboratory remained closed.
Perhaps the inspection delay caused the closure, but the reader has to infer that connection.
If the delay was the reason, we could write:
The inspection was delayed, so the laboratory remained closed.
So presents the closure as a consequence.
We could also place the reason first:
Because the inspection was delayed, the laboratory remained closed.
Or begin with the result:
The laboratory remained closed because the inspection was delayed.
These versions convey the same basic relationship, but they place the reader’s attention differently.
A different connecting word can change the meaning more substantially:
Although the inspection was delayed, the laboratory reopened as scheduled.
Now the reopening happened despite the delay. The sentence no longer expresses the same cause-and-effect relationship.
This is where sentence structure becomes useful beyond grammar exercises. The way clauses are connected can establish a reason, highlight a contrast, or leave two ideas as separate observations. Choosing the right connection helps readers understand not just what happened, but how the information fits together.
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