How To Use Commas in Compound Sentences

Commas in compound sentences serve to assist the joining word in connecting two different ideas in a way that makes sense visually. They go before the joining word to cause a visual break.

Here’s how commas work in compound and other complicated sentences.

Sentence Clauses and Types

Sentences are made of groups of words called clauses. Clauses can be broken down into two categories: independent and dependent. An independent clause is a complete thought and can stand on its own as a grammatically-correct sentence. A dependent clause is a part of an idea, meaning that it relies on another clause to make sense.

  • Jim loved the movie. – An independent clause.
  • Jim loved the movie, as did Maria. – A dependent clause.

Sentences always have at least one independent clause in them. The kind of sentence you have depends on the clauses used to construct it.

  • If an independent clause is the only clause in the sentence, it’s called a simple sentence.
  • A sentence containing an independent clause and one or more dependent clauses is called a complex sentence.
  • A sentence that contains more than one independent clause is called a compound sentence.
  • A sentence with two independent clauses joined by a dependent clause is called a compound-complex sentence.

The most difficult to punctuate sentences are compound and compound-complex.

How To Use a Comma in a Compound Sentence

To join two independent clauses into a compound sentence, you need a way to transition from one clause to the next. This is where the comma comes in. Commas used in conjunction with one of seven joining words – for, and, nor, but, or, yet, and so – indicate a pause in the sentence and a switch from one idea to the next.

To use a comma in a compound sentence, you would place the comma after the first independent clause and before the joining word which starts the second independent clause.

  • Sam wanted to go outside, but his mother said it was too cold.
  • Lea needs to read her book, and she needs to write a report on it.
  • Arthur, get a snow shovel, or you’re going to be trapped inside.

You can also use a semicolon to join the two clauses together in a compound sentence. These sentences don’t require a joining word, as the semicolon acts as enough of a separation.

  • Sam wants to go outside; his mother said it was too cold.

If a compound sentence doesn’t have a joining word in it, then you don’t need a comma.

Using a Comma in a Compound-Complex Sentence

To use a comma in a compound-complex sentence, consider the placement of the dependent clause.

  • The comma goes between the two independent clauses when they are right next to each other.
    • While Tim loves to hike, Jane loves to read, but Adam doesn’t like to do either activity.
  • The commas go around the dependent clause when it is in the middle, and are usually assisted by a semicolon for the other independent clause.
    • Tim, who loves to hike, doesn’t read often; Jane loves to read because she doesn’t like going outside.

To punctuate a compound-complex sentence, add the correct punctuation for each part – the compound sentence and the complex sentence. A compound-complex sentence is really just a combination of the other two.


Using commas doesn’t’ have to be difficult. As long as you remember what a comma does – causes a visual break in the sentence – then you can rely on the trick of reading your sentences out loud to get the punctuation right the majority of the time.