Using commas is confusing to native and non-native speakers alike. Why do we use them? To separate parts of a sentence in order for the sentence as a whole to be more understandable. Think of them as moments when we would naturally take a breath or a short pause if we were reading a sentence aloud. Exactly when and how should we use them? The list of rules is quite lengthy, but I'll give you the four most common uses!
1. To separate items in a list
You're probably very familiar with this one: "Hannah asked for two eggs, sausage, and bacon." We put a comma after each item in a list to separate them from each other. Note: The comma before the "and" here is called the Oxford comma. Using that comma is optional. However, make sure you are consistent. You should either use it all of the time or none of the time.
2. To separate two independent clauses combined by a coordinating conjunction
Wait, wait, wait. Independent clauses? Coordinating conjunction? What are those?? Allow me to explain. An independent clause is a group of words that contains a subject and a verb, and it expresses a complete thought. For example, "I ate a sandwich." "I" is the subject, "ate" is the verb, and together, the group of words expresses a complete thought - you've just learned that I ate a sandwich. A coordinating conjunction is a conjunction that is used to connect words, phrases, and clauses, like in this sentence: "Bob and Jonah went to the beach, but Carl stayed at home." "And" and "but" are coordinating conjunctions. Use the acronym FANBOYS to remember the list of coordinating conjunctions: For, And, Nor, But, Or, Yet, and So.
Back to commas. In the last example I gave, I used a comma before the word "but." "But" connected two independent clauses. "Bob and Jonah went to the beach" has a subject and a verb and expresses a complete thought, and "Carl stayed at home" has a subject and a verb and expresses a complete thought. We use a comma before "but" to connect the two. Here are two other examples: "Sarah was running late, so she gave her boss a quick phone call to warn him." "Brendan dressed up as a fox, and Kyle dressed up as a zebra."
3. To connect a dependent clause to an independent clause
You've learned what an independent clause is (a group of words that contains a subject and a verb and expresses a complete thought). A dependent clause is the same except it does not express a complete thought. For example, "While we were driving" has a subject ("we") and a verb ("were driving"), but it doesn't express a complete thought. It doesn't make sense by itself. What happened while we were driving?? To make this a complete sentence, we can connect it to an independent clause like this: "While we were driving, Ryan spotted a deer." We add a comma after the dependent clause and attach it to an independent clause. Voila, we have a complete sentence!
4. To offset phrases in the middle of a sentence that are not essential to the sentence
Sometimes people add phrases within a sentence to give additional details, but those details aren't necessary. That is the type of phrase we would offset with commas. Here's an example: "Lauren's husband, in case you were wondering, is a pilot." "In case you were wondering" isn't necessary in the sentence. The sentence would still make sense if you simply had "Lauren's husband is a pilot." The addition of the comment is placed between two commas to show that it's a detail that has been included to express further information, but its omission wouldn't change the meaning of the sentence. Here's another example: "Jeremy and Lila, both Psychology majors, met each other in Psych 101."
It was tempting to point out every time I used a comma based on one of the four rules I've provided, but I resisted, and I think this post is a lot cleaner as a result! I hope this helped you feel a little more confident about using commas! If you are interested in receiving more writing tips, especially those of you who are looking for an online ESL tutor, please contact me here!