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Punctuation Basics: How to Use the Comma

Punctuation Series: Colons | Commas | Dashes | Semicolons

I’ve saved the comma for last in this series. It’s probably the most ubiquitous and versatile punctuation mark which means it’s also the most prone to misuse.

Like other forms of punctuation, the comma serves as a tool for separating, clarifying, and creating space between the parts of your sentences. Author Patricia T. O’Conner describes commas as “yield signs that help separate your ideas and prevent pileups. If you ignore one, you could be in for a bumpy ride.” There are more rules for commas than for any of the other punctuation marks. My preference is to focus on the most important applications and not worry too much about the edge cases or more obscure usages.

With that in mind, let’s move onto the primary uses of the comma:

  • As a separator for independent clauses with coordinating conjunctions.
  • As a separator for dependent clauses at the start of a sentence.
  • As a separator for interjections and questions.
  • To mark off non-restrictive clauses (incidental information).
  • For lists and series.

Of course, commas are used in many more instances than those listed above. In order to keep this post manageable and attend to the major use cases, I am omitting common usage such as dates, place names, usage in dialogue and other functions. Additional details on the comma can be found in the reference links listed at the end of the article.

Commas and independent clauses

Commas can be used to combine independent clauses when coordinating conjunctions are used. First, let’s clarify those terms. An independent clause is a standalone sentence. A coordinating conjunction is a connecting words like “and” or “but.” There are seven coordinating conjunctions. They can be remembered by using the mnemonic “FANBOYS”: for, and, nor, but, or, yet, and so.

When you connect the two independent clauses with a comma, you place the comma before the coordinating conjunction.

Examples are the best way to illustrate:

  • I walked down Main Street. I stopped for breakfast.
  • I walked down Main Street, and I stopped for breakfast.
  • I walked down Main Street; I stopped for breakfast.

The list above demonstrates a few ways to handle independent clauses. The first example, presents two separate sentences. The second example uses a comma with a coordinating conjunction. The third example uses a semicolon (which renders a coordinating conjunction unnecessary).

A common error is called the comma splice. A comma splice occurs when independent clauses are connected by a comma without a coordinating conjunction. Per the examples above, the comma splice can be rectified with a coordinating conjunction or semicolon.

It’s also worth noting that if the coordinating conjunction isn’t used between two independent clauses, the comma is not needed (e.g. “I walked down Main Street and stopped for breakfast.”).

Commas and dependent clauses

A dependent clause is a phrase that refers to or provides context to an independent clause. Dependent clauses are frequently used to establish context or setting or to indicate possible cause and effect. The comma helps to set this introductory clause off from the main clause.

Here are some examples:

  • After jogging for an hour, I started to feel pain in my knees.
  • While brushing his teeth, Frank realized he had forgotten to feed the dog.
  • Before I go to sleep, I enjoy a nightcap.
  • Because of the pandemic, I was unable to work for five months.
  • If you have no money, you cannot buy fancy cars.

Note that when the dependent clause trails the main clause, the comma is typically dropped. Here are the previous examples reordered (independent clause follow by dependent clause):

  • I started to feel pain in my knees after jogging for an hour.
  • Frank realized he had forgotten to feed the dog while brushing his teeth.
  • I enjoy a night cap before I go to sleep.

Transition words often signal the use of a dependent or subordinate clause. It’s a worthwhile exercise to become familiar with the variety transition words and their functions.

Commas with interjections and questions

The comma also comes in handy for questions and interjections. These interruptions can appear at the beginning or ending of the sentence. Here are a few examples:

  • That was odd, don’t you think?
  • Hey, what the hell are you doing?
  • You know, I really didn’t appreciate that.
  • Sorry, it was my fault after all.
  • I don’t like him, do you?
  • Hi, pleased to meet you.

Similarly, if you are addressing a person, a comma is also advisable:

  • Mom, the coffee is on the table.
  • Grace, did you hear the news?

Of course, if the situation is urgent, it might make sense to drop the comma:

  • Suddenly, a shot rang out.
  • Suddenly a shot rang out.

Commas and non-restrictive clauses

A non-restrictive clause is a phrase that is not essential to a sentence that imparts additional information, color or detail.

Here are some examples:

  • John, who was larger than most boys his age, ate his sandwich.
  • Mount Washington, tallest in the state, stands at over 11,000 feet above sea level.
  • His girlfriend, Sheila Johnstone, was still in college at the time.

Parentheses and dashes could be used in any of the above. Parenthesis are consider the most discrete way to present a non-restrictive clause. Commas are a bit more overt. Dashes are considered the most conspicuous.

  • John (who was larger than most boys his age) at his sandwich.
  • John, who was larger than most boys his age, ate his sandwich.
  • John—who was larger than most boys his age—ate his sandwich.

Commas and lists

The comma is used to delineate items in a list. Here are some examples:

  • I went to the store to buy milk, peanut butter, and a banana.
  • Sports like basketball, baseball, and soccer are my favorites.

See the list of resources below if you want to explore the great serial comma debate. I opt to use the final comma before the coordinating conjunction so long as it avoids creating any ambiguity.

The comma can also be used to separate a list of adjectives:

  • The mountain was tall, cold, and covered in ice.
  • He was a crafty, acerbic politician.

However, there are instances where commas are not used:

  • The tall copper pot.
  • I saw an old compact car sitting beneath the tree.

One rule of thumb to help determine when commas can be used is to insert the word “and” between adjectives. Another is to try reversing the order of adjectives to see if the description still reads correctly.

In the case of the pot example the following simply don’t work:

  • The tall and copper pot.
  • The copper tall pot.

If you want to dive deeper into the subject of the comma, there are a great number of resources for doing so. I’ve linked to a few that I’ve found helpful.

Here are some additional resources that I found useful on the subject:

  • 8 Comma Rules ( PDF with a good variety of examples
  • Commas: Eight Basic Uses ( Another well-organized PDF with a good variety of examples.
  • Dreyer’s English: An Utterly Correct Guide to Clarity and Style ( Editor Benjamin Dreyer’s grammar guide is a surprisingly fun read. Chapter 3, focused on punctuation, has some interesting thoughts on the comma.
  • Serial Comma ( Excellent overview of the great debate over the serial comma. Includes examples in which the serial comma resolves ambiguity as well as examples in which the serial comma introduces ambiguity.

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