Coordinating Conjunctions

Coordinating conjunctions are joining words that connect words, phrases, or whole sentences together. At this level, you will learn how to use them to join complete ideas called clauses.

What You'll Learn

How to use and, but, or, and so to join two clauses into one sentence
How to choose the right conjunction based on the meaning you want to express
When to use a comma before a conjunction that joins two clauses

When to Use

Adding another idea: "I packed my bag, and my sister packed hers."
Showing a difference: "He studied hard, but he did not pass the test."
Giving a choice: "We can take the MRT, or we can walk to school."
Showing a result: "It was raining heavily, so the football match was cancelled."

How to Form

Joining Two Clauses

A clause is a group of words with a subject and a verb. When you join two clauses with a coordinating conjunction, you are making one longer sentence from two shorter ones.

Two separate sentences	Joined with a conjunction
I finished my homework. I went out to play.	I finished my homework, and I went out to play.
She wanted to swim. The pool was closed.	She wanted to swim, but the pool was closed.
You can have rice. You can have noodles.	You can have rice, or you can have noodles.
The bus was late. We took a taxi instead.	The bus was late, so we took a taxi instead.

What Each Conjunction Means

Conjunction	Meaning	Use it when...
and	addition	both ideas go together or happen one after another
but	contrast	the second idea is surprising or different from the first
or	choice	there are two or more options to pick from
so	result	the second idea happens because of the first

Key Rules

Each clause needs a subject and a verb: Both sides of the conjunction must be complete ideas. "I ate lunch, and I drank water." (correct) -- not "I ate lunch, and water." (that is just a list, not two clauses).
Use a comma before the conjunction when joining two clauses: Write "I was hungry**,** so I ate a sandwich." The comma comes just before the joining word.
No comma when joining just words or phrases: "I like cats and dogs." has no comma because "dogs" is not a full clause.
"But" shows a surprise or contrast: The second idea should be unexpected. "She is young, but she is very brave." The bravery is surprising for someone young.
"So" shows cause and result: The first clause is the reason, and the second clause is what happened because of it. "The alarm rang, so everyone left the building."

Common Mistakes

Wrong	Right	Why
I was tired so I slept early.	I was tired, so I slept early.	Need a comma before "so" when joining two clauses
She likes swimming, and likes running.	She likes swimming and running.	"Likes running" is not a full clause -- just join the words
I want to go but I have no money.	I want to go, but I have no money.	Need a comma before "but" when joining two clauses
He was hungry, so but he ate rice.	He was hungry, so he ate rice.	Use only one conjunction, not two
We can go to the park, and we can go to the library.	We can go to the park, or we can go to the library.	When giving a choice, use "or", not "and"

Clue Words

"And" -- adding ideas together:

also, too, another, as well

"But" -- showing contrast:

however, yet, still, on the other hand

"Or" -- offering a choice:

either, otherwise, instead

"So" -- showing a result:

therefore, as a result, that is why

Tip: Think of these four conjunctions as four jobs: and = plus (+), but = however, or = pick one, so = that is why. Match the job to the meaning of your sentence!

Practice Tips

The two-sentence test: Write your two ideas as separate sentences first. Then pick the conjunction that shows the right connection between them.
Comma check: After you join two clauses, check -- does each side of the conjunction have its own subject and verb? If yes, you need a comma before the conjunction.
Meaning match: Read the joined sentence aloud. Ask yourself: Am I adding, contrasting, choosing, or showing a result? Make sure your conjunction matches.
Swap and check: Try replacing your conjunction with another one. Does the sentence still make sense? If "but" works where you wrote "and", you may have chosen the wrong one.

Quick Reference

Conjunction	Job	Example
and	adds another idea	I read a book, and my brother played a game.
but	shows a difference	The food was spicy, but I still enjoyed it.
or	gives a choice	Shall we eat at the hawker centre, or shall we cook at home?
so	shows a result	She practised every day, so she won the spelling bee.

Rule	Example
Comma before the conjunction when joining two clauses	I was tired, and I went to bed.
No comma when joining words or phrases	I bought apples and oranges.
Each clause has a subject + verb	She sang, and he danced.

Coordinating Conjunctions (P3) (Primary 3)