What is a comma? When should it be used?
A comma (,) is a punctuation mark used to indicate separation within a sentence. They help to group words together and show what parts of the sentence are most important. Some common usages of commas include:
Connecting two independent clauses together with a connecting word
I like to eat sandwiches, and I made one today.
If you have two independent clauses, they can be connected to form one sentence if you add a comma and a coordinating conjunction. There are seven coordinating conjunctions, which can be remembered with the acronym FANBOYS: for, and, nor, but, or, yet, and so. To do this, a comma should be added after the first independent clause and a fitting coordinating conjunction should follow that comma.
For example, if you have the following two independent clauses:
- I like dogs
- I hate cats
Adding a comma after the first clause gives you “I like dogs,” with the comma. The coordinating conjunction that fits best here is “and,” so that would go after the comma. This gives you, “I like dogs, and I hate cats.” Not having a FANBOYS after the comma results in a grammatical error called a comma splice.
In the case that you don’t have a subject and verb on either side of the FANBOYS, you don’t need a comma. In this case, if you got rid of the second “I,” you would instead write, “I like dogs and hate cats.”
Separating introductory words
However, this isn’t true.
Some words may seem like FANBOYS but don’t fit into the acronym. These are introductory words and function a little differently; they should be separated from the independent clause with a comma but shouldn’t be used to connect two independent clauses. One example of such a word is “however.” If you treat it as a FANBOYS and write the sentence, “I like dogs, however I hate cats,” it doesn’t correctly connect the two clauses. Instead, the two clauses would have to be separated by either a period or semicolon (“I like dogs.” or “I like dogs;”) and a comma would follow “however” since it’s an introductory word and not a part of the second independent clause. This gives you, “I like dogs. However, I hate cats.” or, “I like dogs; however, I hate cats.”
Connecting a dependent clause that precedes an independent clause
When I went to the park, I saw a duck.
This usage is fairly straightforward: when you have a dependent clause preceding an independent one, the dependent clause should be followed by a comma. Note that the order of the clauses is important here. If the independent clause comes first, you do NOT need a comma.
Separating nonessential words and phrases
Bobby, a sophomore, likes to go to the Writing Center.
I really like reading novels, especially fantasy.
Sometimes referred to as “interrupters” or “asides,” nonessential words and phrases contain additional information that is separate from the main idea of the sentence. They should be preceded and followed by commas. However, if the nonessential phrase occurs at the end of the sentence, it should be preceded by a comma and followed by a period. Note that these are nonessential phrases, meaning that if they contain information that is central to the main idea of the sentence, they should not be surrounded by commas.
For example, if the main idea of a sentence is, “John likes to cook,” and you want to add
the information that John is a student, you would have, “John, a student, likes to cook.” This is a nonessential phrase because him being a student has nothing to do with the fact that he likes to cook; his profession is an offhand comment that isn’t crucial to the main point of the sentence.
Separating three or more items in a list
I like to read, write, and sleep.
When you have a list of items, they should be separated with a comma, the only exception being the comma that comes after the penultimate list item (in the example sentence, this would be the comma that comes after “write”). This comma is optional and is referred to as the Oxford comma, though it may be a convention for some formats of writing.
Examples of Student Errors and Comments
A sentence that I found in a written feedback that I did for a student with missing commas was:
When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War a common theme or idea I noticed was military strength.
This sentence doesn’t follow the third comma rule listed above (using a comma when a dependent clause precedes an independent clause). The dependent clause is, “When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War,” and the independent clause is, “a common theme or idea I noticed was military strength.”
Assuming that the student has explicit English grammar knowledge, a model comment I’d leave is:
I suggest putting a comma after, “When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War.” This is because this is a dependent clause, while the rest of the sentence following it is an independent clause. Whenever you have a dependent clause preceding an independent clause, a comma should be placed after the former to separate the two clauses. For this sentence, that would give you, “When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War, a common theme or idea I noticed was military strength.”
If the student didn’t have explicit grammar knowledge, I would instead write:
I suggest putting a comma after, “When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War.” This is because this is a dependent clause, meaning that it isn’t a complete thought that can stand on its own. You can tell because after just reading this clause, you’re left with the question, “What happens when examining the woodblock prints and postcards?” Meanwhile, the rest of the sentence is an independent clause, meaning that it is a complete thought that could stand on its own as a sentence. Whenever you have a dependent clause preceding an independent one in a sentence, there should be a comma directly after the dependent clause to separate the two. For this sentence, that would give you, “When examining the woodblock prints of the Sino-Japanese War and the postcards of the Russo-Japanese War, a common theme or idea I noticed was military strength.”
The difference between these two comments is that in the first one, I assumed that the student understood what “dependent clause” and “independent clause” meant, whereas I offered an explanation in the second one. I used this terminology in both comments to broaden the writer’s vocabulary when it comes to meta-language so that they are able to label this type of error in the future. However, I didn’t want to use complicated terminology that the student didn’t understand in the second comment due to thinking that it would turn the student off from making the correction entirely. Since you can’t ask the student what terminology they’re familiar with in a written feedback appointment, I’m more inclined to assume that they don’t have explicit grammar knowledge and give a comment like the second example.
Both comments opened with my main suggestion before going into more detail about why this suggestion is being made. I chose to use the phrase, “I suggest,” instead of something like, “Add a comma…” so the writer didn’t feel like I’m forcing them to do anything. At the end of the day, it’s their writing, and they should have ownership over the edits that are made. I also gave an example of what this sentence would look like with the edit, so the writer knows exactly what I’m suggesting. Due to this being a written feedback comment, I wanted to be as clear as possible with my suggestions. I may not have rewritten each sentence if the writer had multiple instances of the same error, but having a couple of edited examples of their sentences serves as a reference for them to apply these corrections to other areas.