It is important to remember that commas make a writer's meaning clear. When you speak, your tone of voice and pauses punctuate what you're saying, but when you write, your readers have only the printed page to use to understand your meaning. Punctuation marks, like commas, help the reader get the meaning from your writing. This is especially true in the case of compound sentences.
A compound sentence is two or more complete, simple sentences that are joined together by a conjunction. Conjunctions are words like and, but, or, nor, so, for, yet. For a compound sentence to be punctuated correctly, there must be a comma before the conjunction.
Look at these two simple sentences below. Since they are so closely related they can be joined together with a comma and the conjunction so to form a correct compound sentence.
The reason for this is that a comma is not a strong enough mark of punctuation to separate complete sentences. Commas can only be used to separate words, ideas, and phrases.
Two simple sentences joined by a conjunction become a compound sentence. Remember, the comma always comes before the conjunction.
There are two simple
sentences here joined by the conjunction but.
Here you have two simple sentences joined by the conjunction and. These require commas before the and to prevent a run-on sentence.
Be careful not to get confused by a sentence that has a compound verb. This type of sentence has only one subject but two verbs. Since it is just one simple sentence it does not require a comma before the conjunction.
This sentence has one subject (Jim) and two verbs (entered and won), so it does not need a comma before the and because it is not a compound sentence.
This sentence also has one subject (mother) and two verbs (cooked and baked), so it does not need a comma before the and because it is not a compound sentence.
Read, think carefully, and remember:
A compound sentence is two
or more complete, simple sentences that are joined together by a
Click on the Chalk board to practice commas in compound sentences!
There are many other important and useful comma rules that you should know to improve your communication when you write. Follow the links below to the lessons that introduce them: