The comma is widely used in writing and is the most commonly tested concept on the ACT English Test. Therefore, it’s extremely important to understand how to correctly use commas and when to avoid them.

One chapter cannot fully describe everything there is to know about comma usage, which is why you’ll find comma-related information in other sections that discuss FANBOYS, run-ons, sentence structures, etc. The following are a few important comma usage rules not primarily covered in other chapters.

1. Removing Non–Essential Clauses

If a clause can be removed without changing the meaning of the sentence, it needs to be surrounded by commas.

Consider the following examples:

• Her mother, a doctor, was often late.
• Jonah, a fifth-grader, jumps rope on the playground every day.  
• Josh, after thinking for a while, decided to go to law school.
  

Take the orange font clauses out of these examples and you still have three clear and complete sentences. If you aren’t sure whether a clause needs to be surrounded by commas, try crossing it out. If the sentence still makes sense, then the commas are needed; if it doesn’t make sense, then the commas are not needed.

Example: The Tower of London, which was begun by William the Conqueror in 1078, is one of the largest and most imposing fortifications in England.

As you can see, the sentence still makes sense even when you remove the clause in the orange font: The Tower of London is one of the largest and most imposing fortifications in England.

However, if we remove one or both of the commas, then the sentence becomes incorrect.

Wrong: The Tower of London, which was begun by William the Conqueror in 1078 is one of the largest and most imposing fortifications in England.

Wrong The Tower of London which was begun by William the Conqueror in 1078 is one of the largest and most imposing fortifications in England.

Sometimes non-essential clauses can be very long. In such cases, look all the way back to the beginning of the sentence in order to identify the start of the non-essential clause. You will need to cross out a lot of information to test whether a non-essential clause is present.

Example 1
Pets can have pretty funny names sometimes. Tiny Tim my neighbour’s dog is a Great Dane the size of a small horse. When he stands on his hind legs, he’s as tall as I am!
A. NO CHANGE
B. Tiny Tim, my neighbour’s dog, is a Great Dane the size of a small horse.
C. Tiny Tim, my neighbour’s dog is a Great Dane the size of a small horse.
D. Tiny Tim, my neighbour’s dog is a Great Dane, the size of a small horse.

Solution: From the context of the sentence, we can tell that “Tiny Tim” is not the name of a person; it’s the name of the speaker’s neighbour’s dog. Does the sentence make sense without the information conveyed by “my neighbour’s dog”?

“Tiny Tim is a Great Dane the size of a small horse.”

Yes, it does! My neighbor’s dog is non-essential information, so we need to set it apart with commas. The only answer choice that does that is B.

Example 2
London, which was originally built by the Romans along the banks of the Thames more than two thousand years ago contains some extremely modern neighborhoods.
A. NO CHANGE
B. ago; contains
C. ago, containing
D. ago, contains

Solution: If you focus only on the underlined portion of the sentence, you’re likely to get confused. The key is to go back to the beginning of the sentence and recognize that it contains a non-essential clause, as signalled by the word which.

London, which was originally built by the Romans along the banks of the Thames more than two thousand years ago contains some extremely modern neighborhoods.

We need to remove the non-essential clause in blue font. Only option D does this and correctly places a verb (contains) immediately after the comma. D is the correct answer.

Important: Two commas do not always equal a non-essential clause! One common mistake is to assume that the presence of two commas in a sentence automatically indicates a non-essential clause.

Consider the following two sentences:

Correct: London, which was one of the largest and most important cities in Europe during the Middle Ages, remains an important financial and cultural centre today.

This sentence contains a non-essential clause that can be removed without altering its basic meaning.

Wrong: During the Middle Ages, London was one of the largest and most important cities in Europe, and today it remains an important financial and cultural center.

The sentence is wrong if we cross out the information between the commas. The information between the commas is actually the important information and the independent clause.

You need to remove the part of the sentence that you believe is non-essential and read the sentence without it to test. If that doesn’t work, try again with a different part of the sentence. This process is very important.

Example 3 
In 2004, historian and journalist J. Pennelope Goforth came across a silver shopping bag with an envelope inside. The envelope marked “Alaska Commercial Company” immediately caught her attention. For years, Goforth has researched the company, which had controlled Alaska’s waters in the late nineteenth century.
A. NO CHANGE
B. The envelope marked “Alaska Commercial Company,”
C. The envelope, marked “Alaska Commercial Company,”
D. The envelope, marked “Alaska Commercial Company

Solution: The key to answering this question is to recognize that the sentence is referring to one specific envelope. The passage states that Goforth found a shopping bag with an envelope inside. That’s one envelope.

The sentence you’re being asked about can therefore only be referring to that single envelope, not implying that the envelope Goforth found was one of many envelopes. Because the clause “marked ‘Alaska Commercial Company’” describes that one particular envelope, commas must be used. C is therefore correct.

On the other hand, consider this version of the passage:

Example 4 
In 2004, while rummaging in a Seattle basement, historian and journalist J. Pennelope Goforth came across a silver shopping bag filled with envelopes. The envelope marked “Alaska Commercial Company” immediately caught her attention. For years, Goforth had researched the company, which had controlled Alaska’s waters in the late nineteenth century.
A. NO CHANGE
B. The envelope marked “Alaska Commercial Company,”
C. The envelope, marked “Alaska Commercial Company,”
D. The envelope, marked “Alaska Commercial Company

Solution: In this version, the passage indicates that Goforth found many envelopes. The description marked ‘Alaska Commercial Company’ is essential because it specifies which one of the envelopes Goforth found. No commas are therefore needed, making A correct.‍

2. LISTS

A comma rule that everyone is most familiar with is that in lists of three or more items, you must place a comma after every item except the last. This is called a serial comma or the Oxford comma.

Example: The pirate loves Barbados because there’s so much to do, including shopping for eye patches, sharpening his sword, and visiting the pub.

After looking at the last two rules, you might assume that you need to put a comma anywhere you see ‘and,’ but that’s not the case!

For example: James and his brother travel led to Oregon and Washington.

Often, you will see a list that doesn’t look like a list because each item is so long. Be careful here.

Correct: Yesterday, Talia went on a boring first date that she left early and plotted to take over the world using nothing but duct tape and string.

You don’t need commas in this sentence because it only lists two items.

Examples 5 - 6
The history of the English language is a fascinating one that reveals influences from a wide variety of different languages, [5] including French Latin and Anglo-Saxon. This last language came to Great Britain [6] when the country was invaded by Angles Jutes and Saxons groups of people who spoke varieties of German. The country’s linguistic landscape was changed drastically when William the Conqueror invaded and brought with him continental French, which became the language of the courts and nobles.

5.
A. NO CHANGE
B. including French, Latin, and Anglo-Saxon
C. including French, Latin, and, Anglo-Saxon
D. including French Latin, and Anglo-Saxon

6.
A. NO CHANGE
B. when the country was invaded by Angles, Jutes, and Saxons groups of people who spoke varieties of German
C. when the country was invaded by Angles, Jutes, and Saxons, groups of people who spoke varieties of German
D. when the country was invaded by Angles Jutes and Saxons, groups of people who spoke varieties of German

Solutions:
5. If “French Latin” were a language, the sentence would be corrected, but “French Latin” is not a language; “French” is a language, and “Latin” is language. Thus, three things are being listed, and need to use commas to separate items in the list. Thus, the correct answer is B!

6. “Groups of people who spoke varieties of German” is restating the list in a different way. There are three items in the list: (1) Angles (2) Jutes (3) Saxons. We need commas separating these three items. We also need to follow “Saxons” with a comma so that the noun phrase “groups of people who spoke varieties of German” is highlighted as a modifier and is set apart from the main sentence. The only answer choice that does both of these is C.

3. ADJECTIVES

In a sentence with more than one adjective in front of a noun or pronoun, and the order of the adjectives doesn’t matter, you need to separate the adjectives with a comma.

Let’s look at two examples, one where you need a comma and one where you don’t:

• The hot dry desert
• The first female astronaut
  

Which one do you think needs a comma? If you’re not sure, check whether the examples make sense with the order of the adjectives reversed:

• The dry hot desert
• The female first astronaut
  

The first sentence makes perfect sense with the new word order, so it needs a comma: the hot, dry desert.

The second, however, doesn’t work when the order of the adjectives is switched, so no comma is needed: the first female astronaut.

4. Names and Titles

Proper names and titles can be either essential or non-essential to a sentence. Context will decide if we need commas around names and titles or not.

The basic idea here is simple: if the proper name being used is describing the ‘only thing’ in the world, use a comma to offset the name. If it’s not, don’t use commas.

Correct: I went to see Woody Allen’s latest movie, “Midnight in Paris,” with my oldest friend, Jessie.

In the above example, you need a comma after ‘movie’ because “Midnight in Paris” is the only film that could be described as Mr. Allen’s newest movie in theaters and a comma after ‘friend’ because “Jessie” is the only thing in the world described by “my oldest friend.” Make sense?

Example 7
Ada Lovelace and her acquaintance, Charles Babbage, were two of the most influential figures in the history of computer science. After Babbage sketched out his ideas for an “analytical engine,” Lovelace demonstrated that the machine might be able to carry out a variety of complex tasks.
A. NO CHANGE
B. acquaintance Charles Babbage
C. acquaintance Charles Babbage,
D. acquaintances, Charles Babbage

Solution: Let’s cross out the name entirely, and see if the sentence still makes sense: Ada Lovelace and her acquaintance, Charles Babbage, were two of the most influential figures in the history of computer science.

A crucial piece of information is lost: we do not know who Lovelace’s acquaintance was – since she may have had many acquaintances. Also, the reference to Babbage does not make sense, so the name is essential and no commas are required. The answer is, therefore, B.

Example 8
Caribbean-American author, Jamaica Kincaid is also known for being an enthusiastic essayist and gardener. She was born Elaine Potter in St. John’s, Antigua but came to the United States at the age of 17 to work as an au pair in Westchester County, New York. She eventually won a scholarship to Franconia College in New Hampshire but returned to New York City to write. In 1985, she published the novel, Annie John, a semiautobiographical story of a young girl growing up in Antigua.
A. NO CHANGE
B. author Jamaica Kincaid
C. author, Jamaica Kincaid,
D. author Jamaica Kincaid,

Solution: Once again, start by crossing the name out of the sentence to see if it still makes sense: Caribbean American author, Jamaica Kincaidis is also known for being an enthusiastic essayist and gardener.

The sentence loses meaning if we remove the name: it doesn’t tell us who the Caribbean- American novelist is. The name is clearly essential, so no commas are needed. The answer is B.

Example 9
I’ve always been interested in gardening, but until recently, I didn’t have room for flowers or plants. When I moved into a new house last summer, however, I was thrilled to discover that there was enough space in the yard for a garden. There was just one problem - I’d never actually planted one. So I called a friend who had a lot more gardening experience than I did. Luckily, that friend, Jane, agreed to come over the next day.
A. NO CHANGE
B. friend, Jane
C, friend Jane,
D. friend Jane

Solution: When we cross out Jane, the resulting sentence still makes sense: Luckily, that friend, Jane, agreed to come over the next day. Jane is therefore non-essential and the commas are necessary, making the answer A.

Example 10 
Jamaica Kincaid (born May 25, 1949) is a novelist, essayist, and gardener. She was born Elaine Potter Richardson in St. John’s, Antigua but came to the United States at the age of 17 to work as an au pair in Westchester County, New York. She eventually won a scholarship to Franconia College in New Hampshire but returned to New York City to write. In 1985, she published the novel, Annie John, a semiautobiographical story of a young girl growing up in Antigua
A. NO CHANGE
B. the novel Annie John,
C. the novel, Annie John
D. the novel Annie John

Solution: As before, start by crossing out the novel’s title and reading the sentence without it: In 1985, she published the novel, Annie John, a semi-autobiographical story of a young girl growing up in Antigua.

The sentence does not make sense in context because we do not know which novel the sentence is referring to. The information is therefore essential, meaning that commas should not be placed around the title.

But, do we need a comma after the title? The clause that starts with  “a semi-autobiographical…” is a modifier that modifies the noun Annie John. Therefore, a comma is needed. So, the answer is B.

5. Transitions

Using punctuation and transitions can be confusing, but here’s a tip to remember: Place commas around the transition word if it is used in middle of a clause. Transitions words are always non-essential.

Correct: The Tower of London was built during the Norman Conquest. Nearly a thousand years later, however, it still remains standing.

The commas around ‘however’ tell us that if we cross that word out, the sentence will still make sense.

The need for two commas is determined solely by context. If you are unsure which type of punctuation should be used, cross out the word or phrase in question and read the sentence without it.

If the sentence makes sense, the word or phrase is being used non-essential, and two commas must be used. If the sentence does not make sense, or a comma splice is created, a semicolon or period is required.

Important: If it’s used to begin a new clause, a transition should never follow a comma.

Wrong: Independent Clause, Transition, Independent Clause

Correct: Independent Clause; Transition, Independent Clause

Correct: Independent Clause. Transition, Independent Clause

Wrong: The tomato is one of the most popular salad ingredients, however, it is actually a fruit.

Correct: The tomato is a popular salad ingredient; however, it is actually a fruit.

Correct: The tomato is a popular salad ingredient. However, it is actually a fruit.