Sentence Structures

Building sentences

Sentences are like buildings. Some are small and simple, like a single room. Others are big and complex, with many rooms connected together. Knowing how to build different kinds of sentences, called sentence structure, makes your writing clear, interesting and grown-up.

The building block: clauses

A clause is a group of words with a subject (who or what) and a verb (action or being).

There are two kinds:

Independent clause

An independent clause can stand alone as a complete sentence.
– The dog barked.
– We went to the beach.

Dependent clause

A dependent clause cannot stand alone. It depends on an independent clause to make sense. It begins with a word like because, when, although, if, since, after, before, while, unless or until.
– because it was raining (What happened because it was raining?)
– when the bell rang (What happened when the bell rang?)

The four sentence structures

1. Simple sentence

A simple sentence has one independent clause.

• The cat slept.
• My sister and I built a sandcastle on the beach. (still simple: one subject group, one verb)
• The children laughed and played all afternoon. (still simple: one subject, two verbs)

Simple sentences are clear and strong. Short ones create emphasis.

2. Compound sentence

A compound sentence has two (or more) independent clauses. They are joined by:
– a comma and a coordinating conjunction (FANBOYS: for, and, nor, but, or, yet, so), or
– a semicolon ( ; ).

• I wanted to go outside, but it was raining.
• The bell rang, so we lined up.
• Mia likes soccer; her brother prefers hockey.

Each part could be its own sentence.

3. Complex sentence

A complex sentence has one independent clause and at least one dependent clause.

• Because it was raining, we stayed inside.
• We stayed inside because it was raining.
• When the movie ended, everyone clapped.

Comma rule: If the dependent clause comes first, put a comma after it. If it comes second, you usually do not need a comma.

4. Compound-complex sentence

A compound-complex sentence has at least two independent clauses and at least one dependent clause.

• When the storm started, the lights went out, and we lit candles.
• I finished my homework after dinner, but my brother played video games until he fell asleep.

Comparing the four structures

Why use different sentence structures?

Using only one kind of sentence makes writing boring.

All simple:
We went to the zoo. We saw lions. The lions were sleeping. We saw monkeys. The monkeys were swinging.

Mixed:
We went to the zoo, where we saw the lions sleeping in the sun. The monkeys, however, were swinging wildly from branch to branch. It was the best day ever!

Mixing structures:
– makes writing flow smoothly,
– shows how ideas connect (cause, time, contrast),
– keeps readers interested.

How to combine sentences

Combine with a FANBOYS word (compound)

It was cold. We wore our coats. → It was cold, so we wore our coats.

Combine with a dependent clause (complex)

We finished lunch. We went outside. → After we finished lunch, we went outside.

Combine with a semicolon (compound)

The test was hard. I passed it. → The test was hard; I passed it.

Common mistakes

Fragments

A dependent clause on its own is a fragment: Because I was tired. Fix it by adding an independent clause: Because I was tired, I went to bed early.

Run-ons and comma splices

Two independent clauses joined with no punctuation or just a comma: I love pizza, it is my favourite food. Fix with a conjunction, a semicolon or a period: I love pizza; it is my favourite food.

Missing comma

Remember the comma before FANBOYS in compound sentences and after an introductory dependent clause.

Try it yourself

Identify each sentence structure.

1. The baby giggled.
2. The baby giggled, and her brother laughed too.
3. When the clown appeared, the baby giggled.
4. When the clown appeared, the baby giggled, and her brother laughed too.
5. Combine into a complex sentence: The sun set. We built a campfire.

Answers: 1. Simple. 2. Compound. 3. Complex. 4. Compound-complex. 5. After the sun set, we built a campfire.

Study tip

Take a paragraph you wrote recently and label each sentence S, CD, CX or CC. If most sentences have the same label, combine or split a few to add variety.

Quick recap

• A clause has a subject and a verb; independent clauses stand alone, dependent clauses do not.
• Simple: one independent clause.
• Compound: two independent clauses joined by FANBOYS or a semicolon.
• Complex: an independent clause plus a dependent clause.
• Compound-complex: two independent clauses plus at least one dependent clause.
• Mix structures to make writing flow.