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What are Commas For?

Commas can be confusing when writing, primarily because there are so many different rules and uses. However, using commas correctly is extremely important because they can disambiguate or clarify the meaning of sentences that might otherwise be confusing. When taking academic courses that require writing, instructors often pay close attention to comma use, and errors in using them can distract from the positive qualities of a paper. Likewise, employers often evaluate a person’s capabilities based on their clear writing skills, including proper use of commas. For this reason, while comma use may not be the most exciting topic to study, it is a crucial one.

What are the Eight Rules for Commas?

Learning about commas may seem overwhelming, and it is helpful to break down the various uses into eight basic comma rules that can be applied when writing.

Commas are used:

  • To separate elements in a series
  • To separate non-restrictive modifiers
  • After introductory clauses or phrases
  • To set off appositives
  • To indicate direct address
  • To set off direct quotations
  • With dates and numbers
  • With titles and addresses

Comma Usage Rule 1: To Separate Elements in a Series

Writers often include commas in a sentence in a place where they would naturally pause while speaking. This strategy isn’t always effective, and it can actually lead to comma errors, but when listing elements in a series, it is an accurate representation of where commas should be placed. When saying a list out loud, most people include a very slight pause between each item. Commas are inserted into a list to represent this pause and to make clear that two items are not connected to one another. Consider the two sentences below.

  1. I need an orange, apple, and pear.
  2. I need an orange apple and pear.

The lack of commas in the second sentence significantly changes the meaning. Rather than listing three separate kinds of fruit, the second sentence indicates that the speaker needs both an apple and a pear that are the color orange.

The use of commas to separate items in a list is further complicated over what is referred to as the Oxford comma. When creating a list, the Oxford comma is the comma before the last item. This comma typically isn’t required; however, it is very helpful in disambiguating the bracketing of phrases. Compare the sentences below.

  1. I would like to thank my siblings, Kim Kardashian and God.
  2. I would like to thank my siblings, Kim Kardashian, and God.

The lack of an Oxford comma in the first sentence makes it ambiguous. Logically, it is clear that the speaker is not the sibling of Kim Kardashian and God, but in less obvious situations, the absence of a comma in the list could lead to confusion.

Commas can also be used in lists composed of independent clauses. For example, someone might say, “My sister is a great writer, my aunt is an excellent cook, and my mother is a fantastic golfer.”

Comma Usage Rule 2: To Separate Non-Restrictive Modifiers, both Adjectives and Adjectival Clauses

Adjectives and adjectival clauses are often used to describe nouns in sentences. In some cases, they require commas, but it is important to consider whether they are being used as restrictive or non-restrictive modifiers.

When two or more adjectives are used to describe a noun equally, they are referred to as coordinate adjectives. To test whether adjectives are coordinated, consider whether putting “and” between them would change the meaning.

  • Correct: The kind, wise man.
  • Correct: The kind and wise man.
  • Correct: The wise, kind man.
  • Correct: The wise and kind man.

In this example, the adjectives are coordinated because, regardless of the order of the adjectives or the inclusion of the word “and,” the meaning of each sentence is the same.

In contrast, some adjectives build on each other and cannot be separated by “and.” These are referred to as cumulative adjectives. If an adjective is being used to describe another adjective within a noun phrase, then a comma should not be used.

  • Correct: Her light green eyes were sparkling.
  • Incorrect: Her light and green eyes were sparkling.
  • Incorrect: Her green and light eyes were sparkling.
  • Incorrect: Her light, green eyes were sparkling.

Unlike the previous example, the meaning is not retained with the addition of “and.” The word “light” is not a separate modifier of “eyes;” instead, it describes the shade of green, so a comma should not be used.

A similar rule applies when using adjectival clauses. Like adjectives, adjectival clauses modify or describe nouns, but they are dependent clauses rather than words or phrases. Adjectival clauses can be restrictive or non-restrictive, depending on the context and meaning of the sentence. An example is provided below.

Sam Jones, who has brown hair, always sits in this seat.

In this example, the adjectival clause is non-restrictive because it is not necessary information in the sentence. Sam Jones has already been identified by his name, so describing his appearance is simply providing additional information. Compare this with the following sentence.

The student who has brown hair always sits in this seat.

The adjective clause is unchanged, but now it is restrictive because the information is required. The student’s hair color is being used to distinguish him from the other students in the class.

The words “that” and “which” can also be helpful when determining whether an adjective clause should be set off by commas. If an adjective clause begins with the word “that,” commas are not used. However, in general, if the clause starts with the word “which,” commas are necessary.

  • His book, which is on the table, is fascinating.
  • The book that is on the table is fascinating.

In the first sentence, the book has already been identified by the word “his,” so the adjective clause, while it may be helpful, is not required. In the second, the adjective clause is necessary because it identifies a specific book.

Comma Usage Rule 3: After Introductory Phrases and Clauses

Commas are also used to separate introductory phrases and clauses from the main clause of the sentence. An introductory phrase or clause often indicates the time or place something occurs. In the example, “After I eat dinner, I will go to the movies,” the introductory dependent clause “after I eat dinner” is separated from the main clause with a comma. Commas are typically used even if the introductory phrase is only one or two words:

  • After dinner, I will go to the movies.
  • I am eating dinner. Afterward, I will go to the movies.

Note that, in any of these examples, if the order of the main clause and introductory clause or phrase were switched, the comma would no longer be included: “I will go to the movies after dinner.”

Other introductory words include terms like “although,” “since,” and “however,” after which a comma should be used.

  • Although I like coffee, my sister enjoys tea.
  • Since I like coffee, I will drink a cup.
  • I like coffee. However, my sister likes tea.

Comma Usage Rule 4: To Set Off Nouns in Apposition and Other Appositives

Another situation that requires a comma is when using an appositive, or two consecutive nouns that refer to the same entity. Regardless of whether the appositive is a single word or a phrase, a comma should be placed after the first and second noun, as shown below.

  • Mr. Ruffalo, the teacher, did not agree.
  • Mr. Ruffalo, the greatest teacher in the world, did not agree.

Comma Usage Rule 5: To Indicate Direct Address

When directly addressing someone by name or title, a comma should be used to separate the address, regardless of where it is placed in the sentence. To directly address someone means to identify the specific person for whom information is intended.

  • Dr. Banner, you will need to sign this form.
  • You will need to sign this form, Dr. Banner.

This does not apply if the name or title is used as a subject or object in the sentence rather than a direct address. Note the differences between the previous sentences and the ones below.

  • Dr. Banner needs to sign this form.
  • This form must be signed by Dr. Banner.

Comma Usage Rule 6: Inside Quotation Marks (American Rule)

This particular rule applies specifically to American usage. If a quotation, or the use of another person’s exact words, appears in the middle of a sentence rather than at the end, a comma is used inside the quotation marks to separate the quote from the rest of the sentence.

  • Incorrect: The speaker explained that “progress is challenging for everyone”, but we must continue to try.
  • Correct: The speaker explained that “progress is challenging for everyone,” but we must continue to try.

However, this rule does not apply when using British English.

Comma Usage Rule 7: Dates and Numbers

Commas are used within dates and numbers to make them easier to understand. In dates where the month is written out in words (rather than in numerical form), a comma is used between the day and the year. If the date is embedded in a longer sentence, a comma is also included after the year.

  • It snowed on November 15, 1978.
  • On November 15, 1978, it snowed

When writing numbers, commas are used to separate hundreds from thousands, thousands from millions, and each succeeding group of three-place numbers.

  • 6,400
  • 73,000
  • 200,000
  • 5,300,000

Comma Usage Rule 8: Titles and Addresses

When writing an address on one line, each element, with the exception of the zip code, is separated from the next by a comma. For example, the name or title of the addressee is separated from the street name and number. This is true whether the date is written on its own or as part of a sentence. However, if the address is broken into separate lines, this rule does not apply.

  • Bob Smith, 123 Cherry Lane, Smallburg, Vermont 29470
  • Please send the letter to Sarah Jones, 493 Sycamore Drive, Bigtown, NY 97834.

Lesson Summary

Proper use of commas is one of the more difficult aspects of writing in English. However, it is important to understand their purpose and correct usage because commas can disambiguate and clarify the meaning of sentences. Knowing the eight basic rules for commas is essential to effective writing. First, commas are used to separate elements in a series, meaning that, when giving a list, commas should be used between each individual item, no matter whether the item is a word, phrase, or independent clause. The Oxford comma, the comma before the last item in a list, is not generally required, but it can help to clarify meaning. Commas are also used with adjectives and adjectival clauses that are non-restrictive modifiers. In the case of adjectives, commas are used if each adjective modifies the noun equally. These are referred to as coordinate adjectives, which differ from cumulative adjectives that build on each other. A non-restrictive adjectival clause is one that contributes information to a sentence but is not necessary to understand the full meaning. Non-restrictive adjectival clauses can be identified because they typically begin with the word “which” instead of “that“.

In addition, commas are necessary after introductory clauses or phrases, including those that indicate time or place, as well as ones that begin with the words “although,” “however,” and “since.” Appositives, or two consecutive nouns referring to the same entity, also require comma use. When making a direct address, a comma should be placed between the name and/or title and the main clause of the sentence. In American English, commas are used inside direct quotations that come in the middle of a sentence. Commas are used in dates and numbers for the purpose of clarity. Specifically, commas are placed between the different elements of dates (e.g. November 3, 2021) and the parts of a number, meaning hundreds, thousands, millions, subsequent three-place numbers (e.g. 3,420,000). Finally, commas are used to separate each component of an address from the next, with the exception of the zip code.

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