The rules governing commas can be tricky; often, there’s some flexibility for your personal style. For the ACT, the “style” rules either have one “right” answer or are just not tested.
So, for our purposes here, it’s easiest to think of commas as separators: they point out information that, for whatever reason, needs to be set apart from the rest of the sentence. Here are some examples to show you what I mean.
Here, the commas are separating the individual items in a list of three or more items:
Othello didn’t realize that Iago was conniving, two-faced, and evil.
See those commas there? They’re pointing out all of Iago’s finer qualities, of which Othello is unaware. We have to use commas to separate them or the end of the sentence would be a bit of a mushy mess.
(Note: the comma before the “and” is called the “Oxford comma.” In real life, the Oxford comma is largely a matter of style, but it can make certain sentences clearer. On the ACT, always include the Oxford comma in lists. It’s unlikely that an Oxford comma will be the only difference between two answer choices, but the ACT prefers it, so, as far as the test is concerned, so should you!)
You use a comma to separate two adjectives when the word “and” could be inserted between them.
Romeo’s choice to take poison was a rash, foolish decision.
(It was a rash and foolish decision. The comma is necessary.)
Hamlet was a sad young man.
(Hamlet was a sad and young man? No, that sounds odd. Don’t use a comma here.)
Additional (Parenthetical) Information
Let’s say I’m telling you a story about a guy named James. Here’s my beginning:
James is rather fond of “Slim Jim’s.”
A simple enough sentence, no? But it leaves us with a major unanswered question: who is James? Clearly, he must be someone I know, or I wouldn’t be able to discuss his dietary preferences, but I haven’t told you who he is or how I know him.
Well, James is my cousin. I know he likes “Slim Jim’s” because we’re family. I need to put that information into the sentence to satisfy my readers’ burning curiosity about James. I could rephrase it to say “My cousin James is rather fond of ‘Slim Jim’s’,” and it would be 100% grammatical, or I could do this:
James, my cousin, is rather fond of “Slim Jim’s.”
The difference here is one of style, and neither one is “more right” than the other. However, if I’m going to include the information that James is my cousin after I introduce his name, I need to separate it in commas.
The two-commas rule works in many cases. If the extra information isn’t grammatically necessary to the sentence, you can separate it with two — only and always two — commas. (You can also use dashes or parentheses for a similar effect. Again, it’s a style thing, and differences in style won’t be tested on the ACT.)
Here’s another example:
James is rather fond of “Slim Jim’s.” My aunt, however, would rather starve than eat them.
The sentence would be perfectly understandable without the word “however,” but I wanted to include it anyway. It’s additional information, a non-essential word. Therefore, I separate it with two commas.
This point is closely related to the last one. If you’re starting a sentence with a transition or other introductory word or phrase, separate it from the rest of the sentence with a comma.
In my life, I’ve made many mistakes. Very few of them were grammatical.
In case you don’t remember or were never taught, a quick run-down on clauses, phrases, and the differences between the two. Don’t worry, it’s mostly painless.
Phrases are groups of related words that don’t have a subject or verb.
(Examples: “over the rainbow,” “singing in the rain,” “a tale as old as time,” etc.)
Clauses are groups of related words that do have a subject and verb. They come in two types.
Independent clauses are complete sentences.
(Examples: “I think I’ll try defying gravity,” “The sun’ll come out tomorrow, etc.)
Dependent clauses have a subject and verb, but are not complete sentences.
(Examples: “under the sea,” “if I only had a brain,” etc.)
Independent – Dependent
You can use commas to separate independent clauses from dependent clauses. Usually, a dependent clause will have a subordinating conjunction at the beginning. Sadly, there are too many subordinating conjunctions to list them all, but here are some of the most common ones:
until, if, since, because, although, once, as, when, where, why, before, than, that, though, unless
If you see these words (or similar ones) at the beginning of a clause, that clause is dependent and needs an independent clause to be a complete sentence. An example for you (and bonus points if you can name that musical):
Once I’m with the Wizard, my whole life will change.
(dependent clause) (independent clause)
The word “once” in this sentence is the subordinating conjunction. The clause that has the word “once” in it is the dependent clause, so it leans on the other half to make one complete, grammatically correct sentence.
Independent – Independent
In one and only one situation, you can use a comma to separate two independent clauses. This is only permissible if you have a coordinating conjunction immediately following the comma.
If I just made your brain seize up with the grammatical jargon there, don’t worry! I have a nifty mnemonic for you. A coordinating conjunction is one of your FANBOYS:
You can use a comma and one of your FANBOYS to separate two complete sentences. Make sure you’re using the right FANBOYS for your situation, and you will never ever need more than one in a row. (I’m looking at you, students who use “but yet” in sentences! One or the other will do!)
Here’s a few examples:
Most students find grammar dull, so I try to spice it up a bit with silly pop culture references.
I always enjoyed grammar, but I understand why some people might not.
Did you want to continue talking about commas, or should we discuss something else?
ERROR ALERT: COMMA SPLICES
The comma splice is a very common error that, once you learn about it, will spoil your ability to read or write comments on the Internet. I’m very sorry to have to do that to you, but it’s for the good of your ACT score.
Here is an example of a comma splice:
It is physically painful for me to write this sentence, I hope you appreciate it.
See what I did there? I tried to separate two independent clauses with just a comma. Technically, that example is a run-on sentence because I didn’t separate the two clauses properly (either with a period, a semicolon, or a comma and an appropriate FANBOYS). Because it’s a very common error, it looks and sounds right to many students, which is why the ACT loves to test it. Let’s look at an ACT-style example.
Garret and Declan went to the supermarket, they wanted to buy some orange juice.
- NO CHANGE
- supermarket they wanted
- supermarket. They wanted
- supermarket they. Wanted
Our answer would be C, because it’s the only answer choice that properly separates the two clauses in the example. A is our comma splice (which is always, always wrong), B actually makes it worse by removing any separator at all, and D turns a run-on sentence into a nonsensical sentence and a fragment.