Punctuation Guide

This guide contains a brief description of most punctuation marks and their uses within technical writing. For in-depth explanations, consult the Chicago Manual of Style. The Grammar Guide is also available as a resource.

Colons

Colons indicate that whatever comes next will clarify or expand the sentence before it. They can only be attached to independent clauses, not sentence fragments, though whatever follows the colon can be a word, phrase, or even another sentence.

According to Chicago, the first word following a colon is capitalized if the colon “introduces two or more sentences.” They give the following examples:

  • She was furious: she wished the evil prince would leave the kingdom forever. Meanwhile, there wasn’t an egg left in the house and the laundry was waiting.
  • She clung to her wishes: She wished the evil prince hadn’t eaten the golden egg. She wished he would leave the kingdom forever. And she wished someone would do her ironing.

In the first example, the last sentence is not necessarily related to the colon, so the first word is not capitalized. In the second example, however, each sentence relates back to the first independent clause about her wishes, so the first word is capitalized.

Commas

1. Use commas to separate independent clauses when they are joined by coordinating conjunctions (for, and, nor, but, or, yet, so).

Examples
  • Correct: I loved eating peanut butter as a kid, but I discovered I was allergic.
  • Incorrect: I loved eating peanut butter as a kid, I discovered I was allergic.

In the example above, the coordinating conjunction "but" was used to combine the two independent clauses, whereas the incorrect version only had a comma. Both clauses are independent because each has a subject and a predicate.

  • Correct: I need to go to the store because there are no groceries in my house.
  • Incorrect: I need to go to the store, because there are no groceries in my house.

In this example, the correct version has no comma. The word "because" is a subordinating conjunction, which means the second clause is dependent. The phrase, "because there are no groceries in my house," would be a sentence fragment on it's own.

  • Correct: You shouldn't go shopping with us if you don't have money.
  • Correct: If you don't have money, you shouldn't go shopping with us.
  • Incorrect: You shouldn't go shopping with us, if you don't have money.

"If" indicates a dependent clause, so no comma is needed. However, if the dependent clause is placed before the independent clause, as shown in the second correct example, a comma is required.

  • Correct: Bobby plays chess and shoots hoops.
  • Correct: Bobby plays chess, and he shoots hoops.
  • Incorrect: Bobby plays chess, and shoots hoops.

In the first correct example, a comma isn't necessary because it contains only one independent clause. Though there are two verbs, only one subject, Bobby, is present. The phrase, "and shoots hoops," is not a full sentence on its own. In the second correct example, a second subject, "he," is added, which gives the sentence a second independent clause. The clause, "he shoots hoops" is a full sentence on its own; therefore, it needs a comma.

2. Use commas after introductory clauses, phrases, and words that come before the main clause.

Examples
  • Correct: Yes, Sarah was confused.
  • Incorrect: Yes Sarah was confused.

In the example above, the first sentence is correct because a comma separates the introductory word, "yes," from the rest of the sentence.

  • Correct: Confused by the strange phone call, Sarah dialed the number again.
  • Incorrect: Confused by the strange phone call Sarah dialed the number again.

Introductory phrases do not have their own subjects and verbs, so they can't stand as a sentence on their own. Instead, they provide details about the upcoming main clause. As shown above, the commas after introductory clauses allow the reader to understand what the main clause is saying. The incorrect example has no comma, and as such, confuses the reader.

  • Correct: Before we buy the tickets here, let's look at other venues' prices.
  • Incorrect: Before we buy the tickets here let's look at other venues' prices.

Introductory clauses are synonymous with dependent clauses, so the same rules apply. If a dependent clause comes before the independent clause, it requires a comma. This way, readers easily find the main subject and verb. In this example, the correct sentence reads more smoothly than the incorrect one because readers don't have to spend as much time decoding it.

3. Use commas to separate nonessential clauses, phrases, and words from the rest of the sentence. Don’t use commas to separate essential clauses.

Examples
  • Correct: Lucy, unlike Suzie, is already packed for vacation.
  • Correct: Lucy (unlike Suzie) is already packed for vacation.
  • Correct: Lucy is already packed for vacation.
  • Incorrect: Lucy unlike Suzie is already packed for vacation.

The above example features a nonessential clause, "unlike Suzie," so commas must surround it. Nonessential clauses are often referred to as parenthetical elements because they can be removed from the sentence without changing the sentence's meaning, much like phrases in parentheses. For example, the sentence, "Lucy is already packed for vacation," still makes sense. The nonessential clause merely adds more detail.

  • Correct: Everyone hated Bob. He, however, thought they were his friends.
  • Correct: Everyone hated Bob. He thought they were his friends.
  • Incorrect: Everyone hated Bob. He however thought they were his friends.

This example features the nonessential word "however." In this case, "however" adds a transition and a different tone to the sentence, but it is not necessary. As shown in the second sentence, meaning stays the same with or without the nonessential element.

  • Correct: Anyone who fights at this school is immediately expelled.
  • Incorrect: Anyone, who fights at this school, is immediately expelled.

This sentence features an essential phrase. If "who fights at this school" is removed, the sentence's meaning changes; therefore, it should not be encased in commas.

  • Correct: The bread that has mold should be thrown away.
  • Incorrect: The bread, that has mold, should be thrown away.
  • Correct: Bread, which molds quickly, should be eaten soon.
  • Incorrect: Bread which molds quickly should be eaten soon.

Phrases that begin with "that" are usually essential elements, so no comma is needed. Phrases that begin with "which" are usually nonessential, so commas surround them. In the example above, "The bread that has mold" is referencing a specific loaf. "Bread, which molds," just adds more detail about all bread in general, so commas are used.

  • Correct: My aunt Barbara met the newest POTUS, Donald Trump, on Wednesday.
  • Incorrect: My aunt, Barbara, met the newest POTUS, Donald Trump, on Wednesday.
  • Incorrect: My aunt Barbara met the newest POTUS Donald Trump on Wednesday.

The difference between the sentences above is small but important. Barbara is an essential word because the readers need to know which aunt the writer is referring to. Donald Trump is nonessential because the readers know there is only one POTUS. Donald Trump, therefore, is encased in commas, and Barbara is not.

4. Use commas to separate items in a list.

Examples
  • Correct: Tom loves grilling, his family, and his cat.
  • Incorrect: Tom loves grilling his family and his cat.

This example shows the importance of commas. The two sentences above have vastly different meanings, even though the words are the same.

  • Correct: Alice met with the Mormons, Patrick, and Melissa.
  • Incorrect: Alice met with the Mormons, Patrick and Melissa.

Similar to the first first example shown, these two sentences have varying meanings. The first makes it clear that the Mormons are not the same people as Patrick and Melissa, whereas the second sentence is missing its last comma, so the phrase "Patrick and Melissa" becomes a nonessential phrase. The second sentence suggests that Patrick and Melissa are the Mormons Alice is meeting.

The last comma is called an Oxford comma. In some style guides, such as AP, Oxford commas aren't used. In Chicago, however, they are required.

5. Use commas to separate coordinate adjectives that modify the same noun.

Examples
  • Correct: She was a sad, stubborn woman.
  • Correct: She was a stubborn, sad woman.
  • Correct: She was a sad and stubborn woman.
  • Incorrect: She was a sad stubborn woman.

Coordinate adjectives have equal weight in a sentence. In the above example, both adjectives are equally important to the sentence, and they both modify the same noun, so a comma separates them. To discover whether adjectives are coordinate or not, ask two questions: Does the sentence make sense if the adjectives are flipped? Does the sentence make sense if the comma is replaced with "and"? In this case, the answer to both those questions is yes, which means they are coordinate adjectives.

  • Correct: She was a sad elderly woman.
  • Incorrect: She was a sad, elderly woman.
  • Incorrect: She was an elderly, sad woman.

This example fails the two-question test. When the two adjectives are flipped, the sentence doesn't sound as smooth. This is because the word "elderly" has more weight than "sad," which means a comma isn't necessary.

Take note of other rules

The five rules above are the ones most commonly confused. However, commas can be found in other instances, such as with quotations, question tags, dates and addresses, etc. Here are a few quick pointers:

  • Commas go before the final quotation mark. (e.g. She said, "I'm not tired," but she was lying.)
  • Commas precede quotes if the quotation seems independent of the sentence. (e.g. She said that she "never felt tired, even after pulling all-nighters," but Tom knew she was lying, so he replied, "I don't believe you.")
  • Commas precede question tags. (e.g. You're still going to the gym, aren't you?)
  • Words and numbers within dates and addresses are separated by commas. (e.g. He was born on September 24, 1991 in Springfield, Illinois.)
  • Commas before the word "too" are optional when "too" is used as a nonessential element. (e.g. I love you, but I, too, think we shouldn't get married.) When "too" modifies an adjective, commas are not used. (e.g. "I love you too much," not "I love you, too, much.")
Dashes

Note: Screensteps doesn't support em or en dashes, so two hyphens are used in the examples below instead. When inserting em and en dashes, be aware of the software's limitations.

Em Dashes

Em dashes are the width of a capital M. They can be used in place of parentheses, in between appositives, or in place of colons to give more emphasis to certain phrases. Don't put spaces between em dashes. Here's an example:

Upon discovering the errors--all 124 of them--the publisher immediately recalled the books.

To place an em dash in Microsoft Word, type "A--B".

En Dashes

En dashes are the width of a capital N (that is to say, they are slightly smaller than em dashes but longer than hyphens). They represent a range of numbers, dates, or times. It should be read as “to” or “through.” Do not put spaces between en dashes. Do not use en dashes if you introduce the phrase with from or between. Here's an example:

Obama was POTUS from 2008 to 2016. During his first election, the vote was 60--40 in his favor.

To place an en dash in Microsoft Word, type "A - B".

Ellipses

Ellipses show something has been omitted, especially within quotes. Each style guide formats ellipses differently. Chicago's ellipses has a space before and after it, as well as spaces between each dot. Within a sentence, it looks something like this:

Eric said, "No one likes a quitter . . . because quitters ruin the game for everybody else."

Ellipses aren't placed at the beginning of a sentence. When ellipses are placed at the end of a sentence, the final punctuation tags on (with no additional space). A visualization is shown below:

Eric said, "Quitters ruin the game for everybody else . . .!"

Hyphens

Hyphens are used for combination words, such as son-in-law. If used to combine compound adjectives, hyphenate two or more words when they come before a noun and act as a single idea (e.g. world-famous ice cream and small, cheap ice cream carton). If the compound adjectives don't precede their noun, they aren't hyphenated. For instance, country-smoked ham is hyphenated, but the ham was country smoked is not.

Besides that, few hard and fast hyphen rules exist, and as such, there is little consistency. For example, the words cross section, cross-reference, and crosscurrent are all correct. See the Chicago Manual's hyphen list for more details on specific words and phrases.

Parentheses

If an entire sentence is placed within parentheses, the sentence’s final punctuation goes inside the parentheses. Place the punctuation outside the parentheses if its phrase is a fragment, or when citations are used. Detailed examples are shown below:

  • Fifteen noted studies show violence has become an increasing problem within the last eight years (especially within Chicago, Los Angeles, and New York City).
  • Fifteen noted studies show violence has become an increasing problem within the last eight years. (In Chicago, Los Angeles, and New York City, the numbers are nearly twice as high as other cities.)
Quotation Marks

End-of-line Punctuation

Quotation marks are placed after commas and periods but before semicolons and colons, as shown below:

  • Larry described Sarah as "abrasive and rude."
  • Larry described Sarah as "abrasive and rude"; however, he made an effort to be cordial when she was in the room.

Place a question mark or exclamation point within closing quotation marks if the punctuation applies to the quotation itself. Place the punctuation outside the closing quotation marks if the punctuation applies to the whole sentence. The following examples depict this:

  • Phillip asked, "Do you need this book?"
  • Does Dr. Roberts always say to her students, "You must work harder"?

Block Quotations

Don't use quotation marks with block quotations, which are five or more lines or more than 100 words, according to the Chicago Manual of Style.

Preceding Commas

Don't precede a quotation with a comma if the quotation is introduced by a conjunction like that, whether, or if, or when the quote is needed to complete the sentence. If the introductory sentence is technically complete without the quote, a comma should come before it. The examples below show this:

  • My doctor says that "cancer may be rare, but the medical centers prevention techniques should be taken seriously."
  • My doctor says my disease "is more common than most people think."
  • Nancy said, "I'm worried about my health."
Semicolons

Semicolons join two related independent clauses together without using a coordinating conjunction. They’re less powerful than periods, but heavier than commas. For instance, the sentence, “I am awake, but I should have gotten more sleep last night,” can be transformed to, “I’m barely awake; I should have gotten more sleep last night.” In the latter example, the semicolon adds emphasis to the second clause without disconnecting it from the first.

Semicolons in Lists

Semicolons add clarity to complicated lists that use commas within their phrases. The following examples illustrate this principle:

  • I often visit Paris, France; Berlin, Germany; and Johannesburg, South Africa.
  • My neighbors include Eric, the butcher; Thomas, the accountant; and Louis, the firefighter.

Semicolons and Conjunctive Adverbs

When a conjunctive adverb (e.g. however, moreover, nonetheless, otherwise,) links two independent clauses together, a semicolon is needed. Here are a few examples:

  • Alice didn’t have any money in her bank account; however, rent was due tomorrow, so something had to be done.
  • Morris was upset about traffic this morning; in fact, his road rage was out of control.
  • Carl hated waking up in the mornings; even so, he got up at six, so he wouldn't be late for his meetings.