Commas are confusing. We have all had a teacher correct our comma placements on an essay. We then asked ourselves, “How do I even know when to add a comma?”
This is not an easy question to answer, but there are some important things to think about when choosing.
Commas before quotes: When quoting someone or something, introduce your quote with a comma before the quotation marks. For example: Researchers stated, “The data was inconclusive.” Do not do this if you are using the quote as part of the sentence. For example: The participants stated that they enjoyed the exercise classes but “did not enjoy the healthy food videos.”
No commas after the conjunction: In most cases, the comma will come before “but.” This comma placement is meant to separate two parts of the sentence (independent clauses) and usually uses a conjunction (and, but, for, yet, or, so, nor). Think about this comma usage when you are contrasting two things or ideas. For example: The girl loved to play soccer, but did not have any time to practice.
Listing: This may be the area where you are most confident in comma use. Of course you separate the items in a series with commas. But the question is: Do you put a comma before the “and”? Some people say no to this Oxford comma, but if you do not use it, your last two items may be confusing to the reader. For example: Josh bought apples, peanut butter, bananas, macaroni and cheese. Did Josh buy the already prepared macaroni and cheese, or did he buy a box of macaroni and a block of cheese? The Oxford comma will help you differentiate.
Added information phrases: “Worcester, which is an hour from Springfield, has the best food in Massachusetts.” The phrase “which is an hour from Springfield” is just additional information we can take out without changing the overall sentence structure. When you do use this type of phrase, make sure to surround it with commas.
Do not use a comma to separate a subject from a verb (The boy from California, is the best student in the class.), or between verb phrases (We kicked the ball into the air, and began to play the game.)
If you are in doubt about any comma rules, ask for help