- Simple Sentences
- Compound Sentences
- Complex Sentences
- Compound-Complex Sentences
Table of Contents
Sentence Structures
Coordinating conjunctions (FANBOYS)
Semicolon (;) as a coordinating conjunction
Connectors that, if and whether
When to use Who, Whom, and Whose
Relative pronoun vs relative adverb
Sentence Structures
Sentences are built from two types of clauses:
Independent Clauses: Subject + verb. Complete thought. Can stand alone.
Dependent Clauses: Subject + verb. Incomplete thought. Cannot stand alone.
The Four Types
These clauses combine to create four sentence structures:
Simple: One independent clause.
Compound: Two or more independent clauses.
Complex: One independent clause + at least one dependent clause.
Compound-Complex: Two or more independent clauses + at least one dependent clause.
Common Errors
Incorrectly combining clauses creates common errors:
Comma Splice: Two independent clauses joined with only a comma.
❌ I am a student, you are a teacher.
✅ I am a student, and you are a teacher.
Sentence Fragment: A standalone dependent clause left incomplete.
❌ Because I am a student.
✅ Because I am a student, I study every day.
1. Simple Sentence
Simple sentence = 1 independent clause
An independent clause:
Has a subject + verb
Expresses a complete thought
Includes all the complements required by the verb
Examples
✅ She sings beautifully.
Subject: she
Verb: sings
No object is required → complete clause
✅ She bought a book.
Subject: she
Verb: bought
Direct object: a book
Bought requires an object in this context.
❌ She bought.
Incomplete because the required object is missing.
✅ The old man walked home.
One independent clause
Complete thought
Key Point
A simple sentence can be short or long.
Length does not determine the sentence type.
What matters is the number of independent clauses:
1 independent clause = Simple Sentence
2. Compound Sentence
Compound sentence = 2+ independent clauses
Compound sentence = Independent clauses joined by coordinating conjunctions
Coordinating conjunctions (FANBOYS)
for
and
nor
but
or
yet
so
The university increased tuition, but it expanded its financial aid program.
Both clauses can stand alone:
The university increased tuition.
It expanded its financial aid program.
The two ideas are equally important, so we connect them with but.
Semicolon (;) as a coordinating conjunction
A semicolon can also connect two closely related independent clauses.
❌ I was a student, however, I am no longer a student (comma splice)
“However” is a conjunctive adverb, not a conjunction.
✅ I was a student; however, I am no longer a student.
Parallelism
When connecting ideas, make sure the structures are grammatically parallel.
✅ The program aims to reduce costs and to improve efficiency.
✅ The program aims to reduce costs and improve efficiency.
❌ The program aims to reduce costs and improving efficiency.
Key idea:
reduce costs + improve efficiency
→ parallel verb phrases
Correlative Conjunctions
These conjunctions work in pairs:
either...or
neither...nor
both...and
not only...but also
When Should You Use a Compound Sentence?
Ask:
Are the two ideas equally important?
YES → Compound sentence
Use a coordinating conjunction to connect two grammatically equal ideas.
NO → Consider a complex sentence
If one idea is more important than the other, you can subordinate the less important idea and make it a dependent clause.
Equal ideas → coordinate
Unequal ideas → subordinate
3. Complex Sentence
A complex sentence contains:
One independent clause + one or more dependent clauses
A dependent clause, also called a subordinate clause, contains a subject and a verb, but it does not express a complete thought. It cannot stand alone as a sentence. It depends on an independent clause to complete its meaning.
I stayed home because it was raining.
I stayed home → independent clause
because it was raining → dependent clause
because → subordinating conjunction
A complex sentence allows us to subordinate one idea to another. This means that we can make one idea the main point and use the dependent clause to provide supporting information
The students remained calm although the exam was difficult.
The main point is:
The students remained calm.
The information about the difficult exam provides:
background + contrast
This is one of the major advantages of subordination.
Instead of simply placing two ideas next to each other, we can show the logical relationship and relative importance between them.
Dependent clauses can perform three major grammatical functions:
Noun clauses
Adjective clauses / relative clauses
Adverb clauses
Different types of introductory words can signal these different functions.
3.1 Noun Clauses
A noun clause is a dependent clause that functions like a noun. Remember that nouns can function as:
Subjects
Objects
Complements
A noun clause can perform many of the same functions.
Many words can introduce noun clauses. Based on their grammar role in the clause they lead, can be into the following four types.
Subordinating conjunctions if, whether, and that
Interrogative Pronouns
Interrogative Adjectives
Interrogative Adverbs
Connectors that, if and whether
That can introduce a noun clause.
When the that-clause is the object
✅ I know that she is busy.
that she is busy = noun clause
→ It is the object of know.
Because the that-clause is the object, that can be omitted:
✅ I know she is busy.
When the that-clause is the subject
✅ That he passed the exam surprised everyone.
That he passed the exam = noun clause
→ It is the subject of surprised.
When the that-clause is the subject, that cannot be omitted:
❌ He passed the exam surprised everyone.
If and whether can introduce a noun clause
I wonder if he will come.
if he will come = noun clause
→ It is the object of wonder.
She asked whether we should start now.
whether we should start now = noun clause
→ It is the object of asked.
Interrogative Pronouns
Common interrogative pronouns include: who, whom, whose, what, which
I know what she wants (noun clause as an object)
What she wants is unclear (noun clause as a subject).
The same type of clause can perform different grammatical functions depending on where it appears in the sentence.
When to use Who, Whom, and Whose
When who, whom, or whose introduces a noun clause, its grammatical case is determined by its function inside the noun clause. Do not determine the form based on the function of the noun clause in the main sentence.
Who — Subject Case
Use who when it is the subject of the verb inside the noun clause.
The police asked who was driving the car.
who = subject of was driving
It's a mystery who ate the last cookie.
who = subject of ate
Whom — Object Case
Use whom when it functions as an object inside the noun clause.
I found $100 on the table and wondered whom I should give it to.
whom = object of give
She didn't tell us whom she was talking about.
whom = object of the preposition about
They couldn't decide whom to send to the conference.
whom = object of to send
Whose — Possessive Case
Use whose to show possession inside the noun clause.
I found $100 on the table and wondered whose it was.
whose = indicates possession
The teacher asked whose book was left on the desk.
whose = indicates possession of book
Key Rule
Who = subject
Whom = object
Whose = possession
The case is determined by the word's function inside its own clause.
Interrogative Adjectives
Words like whose, which and what can also function as an adjective. Consider:
I don't know which book he chose.
Here, which modifies the noun book.
Therefore, which functions as an interrogative adjective.
But be careful:
The function of which is not the same as the function of the entire clause.
The entire clause is:
which book he chose
The entire clause functions as the object of know.
So:
which → interrogative adjective
which book he chose → noun clause
Entire clause → object of know
Interrogative Adverbs
Noun clauses can also begin with interrogative adverbs such as how, when, where and why.
She asked how he fixed the car.
how tells us the manner in which he fixed the car.
Inside the clause:
how = adverb
But the entire clause:
how he fixed the car
functions as the object of asked.
She asked me when I could visit her.
Inside the clause:
when = adverb
But the entire clause:
when I could visit her
functions as the object of asked.
Always distinguish between:
the function of an individual word inside the clause
and
the function of the entire clause in the main sentence.
3.2 Adjective Clauses
An adjective clause, also called a relative clause, is a dependent clause that modifies a noun or pronoun. Relative clauses provide additional information about a noun.
They can be introduced by relative pronouns and relative adverbs.
Relative Pronouns: who, whom, whose, which, that
Relative Adverbs: where, when, why, how
Relative Pronouns
We can often create a relative clause when two sentences share the same person, thing, or idea.
The boy is my brother.
He is playing soccer.
Both the boy and he refer to the same person.
We can combine them:
The boy who is playing soccer is my brother.
Here:
who is playing soccer
is the relative clause.
who replaces “he.”
Relative pronouns replace a noun inside the relative clause. Because they replace a noun, the clause would have something missing without the relative pronoun.
The man who lives next door is a teacher.
who replaces “he.”
Inside the relative clause:
who lives next door
who functions as the subject of lives.
Relative Adverbs
Relative adverbs do not replace a noun. Instead, they provide information about place, time, reason, or manner.
This is the place where I met her.
The clause:
where I met her
describes the place.
The clause after where is grammatically complete:
I met her.
“where” tells us where the action happened. These are more examples with relative adverbs:
I remember the day when we first met.
This is the reason why I won.
Relative pronoun vs relative adverb
Consider these two sentences:
This is the house that I live in.
This is the house where I live.
They have essentially the same meaning, but the grammatical structure is different.
With "that"
that I live in
The clause needs an object after the preposition in.
I live in the house.
that represents the house.
With "where"
where I live
The clause itself is complete:
I live.
where provides information about the place.
Quick Test
Ask: Is a subject or object missing inside the relative clause?
If yes, you may need a relative pronoun.
If the clause is complete and the word expresses place, time, reason, or manner, you may need a relative adverb.
3.3 Adverb Clauses
An adverb clause is a dependent clause that functions like an adverb.
It provides information about the relationship between ideas.
Adverb clauses can express time, reason, condition, contrast, purpose and manner.
They are introduced by subordinating conjunctions.
Subordinating Conjunctions: because, although, if, since, until, before, after, while, unless
I stayed home because it was raining.
We left the park when it started to rain.
I am asking since you know the answer.
Although he was tired, he kept working.
You can't succeed unless you try.
4. Compound-Complex Sentence
A compound-complex sentence combines the structures of a compound sentence and a complex sentence.
Structure
2 or more independent clauses + 1 or more dependent clauses
Because it was raining, I stayed home, and my brother watched a movie.
Because it was raining → dependent clause
I stayed home → independent clause
my brother watched a movie → independent clause
So:
1 dependent + 2 independent clauses = compound-complex sentence
A compound-complex sentence does not have to contain an adverb clause.
It can also contain a noun clause.
I know what she wants, and my brother knows what she needs.
Independent clauses:
I know what she wants
my brother knows what she needs
Noun clauses:
what she wants
what she needs
Both noun clauses function as the objects of know.
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