B. Foundations of Language · Cursive, Spelling and Sentences

Simple, Compound and Complex Sentences

B3.1 B3.3About 40 minutes

Learning goals

I can find the subject and the predicate in a simple sentence.
I can join two simple sentences into a compound sentence with a comma and and, but, or or so.
I can write a complex sentence using a clause that starts with when, because, after, before, if, while, until or although.
I can put a comma after an adverb clause that comes first.

Words to know

subject
The part of a sentence that tells who or what the sentence is about.

predicate
The part of a sentence that tells what the subject does or is. It includes the verb.

simple sentence
A sentence with one complete idea: one subject and one predicate.

compound sentence
Two simple sentences joined with a comma and a joining word like and, but, or, so.

clause
A group of words with a subject and a verb.

complex sentence
A sentence with a main idea and an extra clause that can't stand alone, like when it snows or because I was tired.

adverb clause
A clause that tells when, why, where or under what condition, like after lunch ended.

Remember from Grade 2

You learned four kinds of sentences: telling (statement .), asking (question ?), command (do this!) and exclamation (wow!). You joined sentences with and, but, or, so, and told why with because.

In Grade 3, you will learn the three forms of sentences: simple, compound and complex. Using all three makes your writing sound smooth and interesting.

Simple sentences: subject + predicate

Every complete sentence has two parts:

The subject: who or what the sentence is about.
The predicate: what the subject does or is.

In The beaver built a dam, the subject is The beaver and the predicate is built a dam.

A sentence with just one subject and one predicate is a simple sentence. A simple sentence can still be long: The busy brown beaver built a big dam across the creek.

Subject (who or what?)	Predicate (does or is what?)
The beaver	built a dam.
My little sister	is six.
Three Canada geese	flew over the lake.
We	skated at the outdoor rink after school.

Simple sentences

Compound sentences

A compound sentence joins two simple sentences. Each part could stand on its own. Put a comma before the joining word:

and adds more: Leo raked the leaves, and Ana jumped in them.
but shows a difference: I like hockey, but my brother likes soccer.
or gives a choice: We can go sledding, or we can build a snowman.
so tells what happened as a result: It was cold, so we wore our toques.

A compound sentence = complete idea + comma + joining word + complete idea. Each joining word does a different job.

Complex sentences

A complex sentence has a main idea (a clause that can stand alone) and an adverb clause that can't stand alone. The adverb clause starts with a word like:

when, after, before, while, until, because, since, if, although

The adverb clause tells when, why or under what condition something happens:

We will go to the park when the rain stops. (when?)
Sam was tired because he stayed up late. (why?)
If it snows tomorrow, we will go sledding. (on what condition?)
Although it was cold, we played outside. (even though...)

A compound sentence joins two complete ideas. A complex sentence has a main idea and a clause that can't stand alone.

The comma trick

If the adverb clause comes first, put a comma after it: When the bell rang, we lined up.
If the main idea comes first, you usually don't need a comma: We lined up when the bell rang.

Don't leave a clause alone

Because it was raining. is not a complete sentence. It leaves the reader waiting: Because it was raining... what? Join it to a main idea: We stayed inside because it was raining.

Worked example

Let's combine two ways

Join these sentences: The snow melted. We rode our bikes.

Compound: use a comma and a joining word. The snow melted, so we rode our bikes.
Complex: use a clause word. After the snow melted, we rode our bikes.
Check the comma: the After clause comes first, so it has a comma after it.
Another complex way: We rode our bikes after the snow melted. (No comma needed.)

The snow melted, so we rode our bikes. (compound) or After the snow melted, we rode our bikes. (complex)

Worked example

Let's sort sentences

Is each sentence simple, compound or complex?

My cousin lives in Winnipeg.
My cousin lives in Winnipeg, and she visits us every summer.
When my cousin visits, we go canoeing.

1 has one subject (My cousin) and one predicate: simple.
2 has two complete ideas joined by , and: compound.
3 has When my cousin visits, which can't stand alone, plus a main idea: complex.

1 simple, 2 compound, 3 complex

Just for fun

Why did the two simple sentences become best friends?

They found something to hold them together: a **comma and an and**!

Hands-on activity

Sentence building strips

You need: strips of paper, a pencil, and a family member.

Each person writes 3 simple sentences about your day or the season, each on its own strip. (The leaves are red. We carved a pumpkin. It was windy.)
On small cards, write joining words: , and · , but · , so · when · because · after · if · although.
Pick two sentence strips and a joining card. Put them together to make a compound or complex sentence. Read it aloud. Does it make sense?
Try moving the clause to the front: Because it was windy, ... Remember the comma!
Write your three best sentences in your notebook (in cursive if you like!).

Your turn

Find the subject and predicate: The hungry raccoon tipped over the bin.

Join with but: I wanted to skate. The ice was too thin.

Join with so: It was raining. We played a board game.

Is this simple, compound or complex? We put on our boots before we went outside.

Add a main idea: When the snow melts, ...

Fix this: Because the bus was late.

Add the missing comma: If you finish your work you can read a book.

More practice: warm-up

Find the subject: My grandpa makes bannock.

Find the predicate: The puppy chased its tail.

Which joining word gives a choice: and, but, or, so?

Is this simple or compound? The moon is bright.

Name two words that can start an adverb clause.

More practice: on your own

Join two ways (compound and complex): Ella was hungry. She ate an apple.

What does the adverb clause tell in this sentence: when, why or on what condition? We will go to the beach if it is sunny.

Is this compound or complex? Ravi played goalie, and Zoe scored a goal.

Rewrite with the clause first: We sang songs while we waited for the bus.

Write a complex sentence that starts with Although.

Challenge

These sentences are choppy: It was Saturday. We went to the market. We bought maple syrup. It was delicious. Rewrite using one compound and one complex sentence.

Which sentence is not complete? (a) After the game ended. (b) The game ended. (c) The game ended, and we cheered. Explain.

Why does When I got home, I made a snack. have a comma, but I made a snack when I got home. doesn't?

Check your understanding

Quiz

What is the subject of The tall maple tree lost its leaves.?

Which is a compound sentence?

Which is a complex sentence?

Where does the comma go? After we ate lunch we went for a walk.

Which joining word shows a difference?

Which is not a complete sentence?

In We will play outside if it stops raining, what does the adverb clause tell?

For parents and teachers

Big idea: Grade 3 students identify and construct simple, compound and complex sentences containing adverbial clauses (B3.1). An adverbial clause starts with a word like when, because, after, if or although and tells when, why or under what condition. The comma after an introductory clause links to B3.3.

How to help at home:

When your child writes several short sentences, ask: "Can you join two of these?"
Play "finish my sentence": you say When the bell rings... and they finish it.
Read aloud and point out long sentences in books. Ask which part could stand alone.

Common difficulties:

Fragments: writing Because I was hungry. alone. Ask: "Because you were hungry... what happened?"
Run-on sentences: joining many ideas with and then, and then. Help break them up and choose better joining words.
Missing commas after an introductory clause, or a comma in place of a joining word (It was cold, we went inside). A comma alone can't join two sentences.

(The terms compound and complex may sound grown-up, but Grade 3 students learn them. What matters most is that your child can write each kind.)