Commas Before Joining Words
Use a comma before a coordinating conjunction (and, but, or, so, yet) when joining two independent clauses in a compound sentence
What a learner can do afterwards
- Place a comma before the coordinating conjunction in a compound sentence, e.g. 'I wanted to go outside, but it was raining'
- Distinguish compound sentences (two independent clauses) from simple sentences with compound predicates, e.g. 'She sang and danced' needs no comma but 'She sang a song, and he played the piano' does
- Edit writing to insert missing commas before coordinating conjunctions in compound sentences
1 · Read
A compound sentence joins two complete thoughts, sentences that could stand on their own, with a small joining word like and, but, or, so, or yet. When you join two complete thoughts this way, put a comma right before that joining word.
I wanted to go outside, but it was raining. Both 'I wanted to go outside' and 'it was raining' are complete thoughts, so the comma goes right before 'but.'
Watch out for sentences with just one subject doing two things, like 'She sang and danced.' That is a compound predicate, not two complete thoughts, so it does not need a comma. Only add the comma when each side could be its own sentence.
Try this test: cover up the joining word and read each side alone. If both sides sound like a full sentence, add a comma before the joining word.
Add a comma right before and, but, or, so, or yet only when both sides could stand alone as their own sentence.
More to read
Commas in compound sentences
### What is a compound sentence?
A compound sentence is made when you join two complete thoughts. Each thought is called an independent clause, and it could stand alone as its own sentence.
For example, "I wanted to play outside" is a complete thought. "It started to rain" is also a complete thought.
### How do you join them?
One easy way is to use a comma followed by a joining word like and, but, or, so, or yet. The comma always goes BEFORE the joining word, like this:
> I wanted to play outside, but it started to rain.
Look closely: the comma comes first, then the word "but."
> Twinkies were once banana-flavored, but the flavor was changed to vanilla.
Both sides of the comma are complete thoughts. That is the big clue. If each side could be its own sentence, you need the comma before the joining word.
Coordinating conjunctions
### What are coordinating conjunctions?
Coordinating conjunctions are joining words. They connect two words, phrases, or complete thoughts that are equally important.
There are only seven of them in English. You can remember them with the word FANBOYS:
* F = for * A = and * N = nor * B = but * O = or * Y = yet * S = so
### The comma rule
When one of these words joins two complete thoughts, put a comma right before it:
> Maya finished her drawing, and she showed it to her class.
But if the joining word only connects two words or short phrases (not two complete thoughts), you do not need a comma:
> Maya finished her drawing and put away her pencils.
In that sentence, "put away her pencils" is not a complete thought, so no comma is needed.
Compound sentences
### What is a compound sentence?
A compound sentence joins two or more complete thoughts into one sentence. A complete thought has a subject and a verb, and it makes sense all by itself.
### Way 1: comma plus a joining word
You can join two complete thoughts with a comma and a coordinating conjunction. The coordinating conjunctions are for, and, nor, but, or, yet, and so.
> The dog barked loudly, and the cat ran up a tree.
Notice the pattern: complete thought + comma + joining word + complete thought.
### A quick check
Cover the joining word and read each side alone. Does each side sound like a full sentence? If yes, add the comma. If one side is missing a subject or cannot stand alone, skip the comma.
> The dog barked and growled. (No comma. "Growled" is not a complete thought.)
When and How to Use a Comma Before and After "But"
### When do you put a comma before "but"?
Put a comma in front of "but" when it connects two complete thoughts. A complete thought has a subject and a verb, and it could be its own sentence.
> I wanted a snack, but the cupboard was empty.
Both sides work alone: "I wanted a snack." and "The cupboard was empty." So the comma goes before "but."
### When do you skip the comma?
If what comes after "but" is not a complete thought, leave the comma out.
> I wanted a snack but found nothing.
"Found nothing" cannot stand alone as a sentence, so no comma.
### What about a comma after "but"?
Usually you do not need one. Only add a comma after "but" if an extra phrase is being tucked in right after it.
Run-ons and comma splices
### Two mistakes to watch for
A run-on sentence happens when two complete thoughts are squished together with nothing to separate them. It needs a fix.
Wrong: "I finished my homework I went out to play."
A comma splice is another mistake. It happens when you use only a comma to join two complete thoughts. A comma by itself is not strong enough.
Wrong: "I finished my homework, I went out to play."
### The fix
Use a comma AND a joining word together:
Right: "I finished my homework, and I went out to play."
Remember the rule: a comma alone cannot do the job. It needs a helper word like and, but, or, so, or yet.
2 · Watch
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