Punctuation—periods, commas, colons, semicolons, all that jazz—might seem like a little thing,^[1] but each point and mark says something to the reader and helps them understand how your ideas are assembled and organized. When you don’t use them correctly, you send all the wrong signals to your readers and make it harder for them to make it through your writing. However, when they are used correctly, punctuation marks fade into the background and nearly disappear as your reader focuses on what you have to say. So, let’s make sure we’re on the same page with the basic punctuation rules.

Periods .

The period, also called a “full stop” in other countries, is the most common punctuation mark used in written English. It has a number of uses, including some rare ones, but since it’s the most basic one to understand, we’ll start here.

Declarative sentences and commands

Whenever you finish a declarative sentence, you put a period after the last word. A declarative sentence is one that states information for the reader. Commands also end with a period.

If your sentence directly asks a question, don’t use a period; use a question mark instead.

A sentence with an indirect question still ends in a period, though.

When you want to add some emotion, excitement, or emphasis to a statement, use an exclamation point instead of a period. Consider the difference between these two sentences:

While the first sentence is simply relaying information, the second has some added element of emotion. Perhaps the speaker is surprised that Marvin is taking them to the bridge instead of some other, more expected destination, or maybe the speaker is surprised that Marvin was given the job instead of someone else.

Abbreviations and initials

There is a decent amount of variation in the use of periods with abbreviations and initials, so you’ll want to make sure you consult the specific style guides that apply to your writing situation, but these are the most common uses. Whenever you shorten a word, you place a period after the abbreviation.

Other terms that are frequently abbreviated need a period after them. Dates that are shortened, such as months (e.g., Aug. or Dec.) or days (e.g., Wed. or Fri.), need a period. When a name is replaced by just an initial, it should also have a period after it, no matter which name is being shortened (e.g., Michael B. Jordan, J. J. Abrams, or J. R. R. Tolkien). However, when a person or a company is regularly referred to entirely by their initials, the periods are typically omitted (e.g., MLK, FBI, or CIA).

Commas ,

A lot of students get to this point of their education without ever getting much explicit teaching or training on how to use a comma. Comments I have heard from students over the years have shown that there’s a lot of misinformation out there about commas. I’ve heard that commas indicate where you should pause in a sentence^[2] or that they join things together in your sentences. However, the real function of a comma is to separate elements within a sentence, so let’s take a look at a number of basic uses of commas.

After an introductory phrase or clause

Any time you start a sentence with something other than the person or thing doing the action,^[3] you need a comma after that thing to tell the reader that the introduction is over and the main part of the sentence is beginning.

It really doesn’t matter what kind of thing you start your sentence with. It could be a word, a phrase, or an entire subordinate clause, but if it’s not the subject, you always^[4] need a comma when you’re ready to start the main clause of the sentence.

Between independent clauses

When you want to join two independent clauses together in your sentence, you need to use a coordinating conjunction to show how those ideas are related. There aren’t that many coordinating conjunctions in English, and there’s really only four you need to know: and, but, or, and so. The others—for, yet, and nor—don’t get used all that often anymore, but luckily, if you take the first letter of all of them, they spell the word “FANBOYS,” which is a nifty little mnemonic device you can use to remember them all. When you use one of these conjunctions to join two clauses together, you also need to use a comma before the conjunction.

One way to determine whether you need the comma before conjunctions like “and” or “or” that are also commonly used to join other kinds of things together is to check and make sure that the words before the conjunction form a complete sentence and that the words after the conjunction also form a complete sentence. If they do, you are joining independent clauses together, and you need to have a comma before the conjunction.

Between items in a series

Grammatically, a series is three or more things listed one after the other. For example, if I say that I really like ice cream, cookies, and chocolate, then those three sweets would form a list. When you write a series, you use a comma to separate each of the items in that list. It doesn’t matter what those three things are, really. They could be nouns, verbs, prepositions, phrases, or even clauses^[5]—if there are three or more of them, then you need commas between each of them, just like I did at the beginning of this sentence.

If it’s possible for you to imagine a disagreement about writing so big that it results in a giant gang fight with crusty old academics, editors, and other writing professionals hurling flaming books at each other and getting all shivvy with sharpened pens, then you should absolutely imagine that they are fighting about one of these commas. The very last comma in a series—the one that goes right before the “and”—is called the Oxford comma.^[7]

One side of this divide maintains that the Oxford comma should always be used at the end of a series of things, while the other side says that the first side is stupid and wasting a lot of space and ink by putting in commas that don’t need to be there because the conjunction makes it clear that you’ve reached the end of the list.^[8] Here are a couple of examples of a series, first with the Oxford comma and then without it:

There’s not much of a difference there, right? Most of the time, there isn’t. However, there are some times when the omission of the comma—or the use of the same—can cause some ambiguity and confusion. In this next example, how many people^[9] did Arthur chat with, four or two?

Without an Oxford comma, it looks like he chatted with two mice that are named Slartibartfast and Ford. If you put in an Oxford comma, it’s clear that he is chatting with four distinct individuals: two white mice whose names we don’t know, a man named Slartibartfast,^[10] and his friend Ford.

There are also times when using the Oxford comma can produce similar amounts of ambiguity and confusion. In the following example, how many people did Arthur travel with?

How many did you count? With the Oxford comma in place, Arthur could be traveling with either three people—a woman named Trillian, a robot without a name, and a guide who is also unnamed—or two people, one of whom is a robot. If we leave out the Oxford comma, things become even more complicated, because now, Arthur might also be traveling with just one companion named Trillian who is both a robot and a guide.

This is why people have been fighting about this for over a century, and that is also why this is my new favorite quote on the subject: “There are people who embrace the Oxford comma, and people who don’t, and I’ll just say this: never get between these people when drink has been taken.”^[11]

So, there’s lots of disagreement over this, and lots of people with very passionate opinions saying lots of nasty things about the lots of people with equally passionate opinions about the other thing, but here’s the good news: none of their opinions matter. You can decide to use or to skip the Oxford comma as much as you want in your personal writing, but when it comes to academic writing, you don’t get to choose.^[12] Your academic writing will always have a specific style that it needs to follow, and that style will dictate whether you’re supposed to use the Oxford comma or not. In the case of MLA and APA styles, they both require that you use it, so there you go. No need to do the research to figure out which side is best^[13] because other people have already decided what you have to do.

Around nonrestrictive clauses and phrases

Sometimes, when you write, you need to add extra information to a noun so that people know who you’re talking about. For example, I have three brothers. If I say, “I called my brother yesterday,” you won’t know who I’m talking about, so I need to add some extra details to that sentence to make it clear which brother I’m referring to: “I called my brother David yesterday.” In this case, the word “David” restricts which of my brothers I could be talking about, which is why that particular detail is considered restrictive.

If we can use restrictive information in our writing, then we can also use nonrestrictive information. These are extra details that are not necessary for determining who we’re talking about, and so, really, they could be ignored and the meaning of the sentence would not change. For another example, I have exactly one son, so I could write, “My son got his driver’s license this week,” and you would know who I’m talking about. Alternatively, I could add a little more detail to the sentence if I wanted and say, “My son, Hyrum, got his driver’s license this week.” Now, you don’t actually need to know his name in order to know which of my one sons I’m referring to, and so that detail does not restrict which son I’m talking about, which is why it’s called nonrestrictive information. I could remove his name from the sentence and you’d still be able to know who the new driver on the streets is.

In the examples above, adding my brother’s or my son’s name to the sentence renames the nouns “my brother” and “my son” for the reader, so their names are being used as an appositive,^[14] but that’s not the only kind of nonrestrictive information you can include. Noun phrases and clauses can also be both restrictive and nonrestrictive.

In the first example, “the planet” does not adequately identify which planet we are referring to, so when we add the adjective clause “which we are currently orbiting” to that noun, it restricts which of all the planets we could possibly be referring to, so it is restrictive. In the second example, since we already have the name of the planet, the noun phrase “the planet which we are currently orbiting” does not restrict which planet we are talking about—the name does that all by itself—so it is nonrestrictive.

How does this apply to commas? When you include nonrestrictive information in a sentence, you surround it with commas. This separates it from the rest of the sentence and shows the reader that it isn’t strictly necessary. Nonrestrictive information can be removed from the sentence without changing the meaning of the original. Here are some additional examples:

These examples use nonrestrictive phrases and clauses to provide additional but unnecessary details for the reader to expand on what they are saying. We don’t need to know that Marvin is a Paranoid Android in order to know who the writer is referring to because the robot’s name gives us enough information already. Similarly, we don’t need to know that humans believed themselves the smartest creatures on the planet in order to know which humans the writer is referring to. In both cases, because the information is nonrestrictive, it is surrounded by commas.

In these two examples, the additional details provided are needed in order to identify the writer’s reference. In the first, we don’t know which giant computer the writer is referring to until we get the details about how it was tasked with determining the Answer, and it is unclear which man is being discussed until we read what his assignment was. In both of these cases, there are no commas around the extra information because it was restrictive.^[15]

With direct address

When your writing includes conversation, there may be the need for one person to speak directly to another. In this case, whenever one person directly addresses the other, you separate the name from the rest of the sentence with a comma.

In the first three examples, the names are being used to directly address those characters, and as such, they are separated from the rest of the sentence by commas. In the last example, Arthur is not being directly addressed. Instead, he is the subject of the sentence, so no commas are used.

With direct quotation

When directly quoting someone in your writing, if you include the name of the speaker and a verb of speech, then you separate that from the rest of the quote with commas.

With numbers, titles, dates, and addresses

When writing numbers 1000 or greater, you typically use a comma every three digits. Numbers that are four digits long can be written both with or without the comma.

If you include someone’s title or credentials after their name, separate them using commas.

When you include a full date in your writing, separate the year using commas.

If you write a full address in your text, separate each element of the address (number and street, city, state and ZIP) except for the ZIP code using commas.

Quotation marks “”

A lot of students get to this point in their education thinking that they already know everything that there is to know about using quotation marks,^[16] but it’s still useful to review all of the ways to use quotation marks to make sure you’ve got it all straight.

To directly quote someone’s writing

This is the most basic use of the quotation mark in academic writing. If you want to use someone else’s writing in your essay, you must enclose their words in quotation marks. This tells the reader that what you are giving them is an exact reproduction^[17] of what the other author wrote. This is typically accompanied by a citation of some kind that helps the reader find the information that will lead them to the actual source you took the words from.

Note that, in the second example, no quotation marks are used because the author merely summarizes what the Guide says instead of quoting it directly.

To write speech

Whenever you wish to write down what someone said or is saying, you need to enclose their words in quotation marks.

If you want to represent someone’s thoughts in writing, you have a choice. Some writers will use quotation marks and a verb of thinking to represent thoughts, while others will use italics to represent thoughts instead of quotation marks.

To name short works

Whenever you mention the name of a short published work, you need to enclose the title of that work in quotation marks. Short works include poems, songs, essays, articles, and chapters—basically, any work that is part of a larger volume should be written in quotation marks. The name of the larger, entire volume^[18] should be written in italics.

To use a word sarcastically, ironically, or skeptically

This is a somewhat uncommon use of quotation marks, but it’s also kind of a fun one. When you want to imply that the word you’re using doesn’t really mean what people think it means, you enclose that word in quotation marks. Here’s an example:

In this example, the quotation marks around the word “poetry” indicate that the writer is using it in a very different way from the normal meaning of the word. Here, the suggestion is that the Vogon poetry is nothing like any normal poetry, which people tend to find interesting and enjoyable.

This use of quotation marks has a fun name: scare quotes.^[19] The marks themselves serve to show the reader that the author is creating some distance between what the word or phrase means and how they’re using it. They kind of suggest that the word does not mean what it actually means. They are actually the origin of the “air quotes” gesture that people do when talking when they’re wanting to put some sarcastic meaning on the word.

This might seem like an easy usage of the marks, but it’s one that people making signs get wrong all the time, so it’s definitely worth reviewing. Here’s another example, but this one shows what you should not put on a sign:

Remember what scare quotes do to a word: they tell the reader that the word within the quotes does not hold the usual meaning. So, what are these “apples” that they are selling, and just how scared of them should we be? Because they’re definitely not apples—they’re “apples.”^[20]

To talk about words

If you want to talk about a word instead of using the word’s actual meaning, you should enclose the word in quotation marks. You can also do this to talk about a single letter or a phrase.

To separate a nickname from a full name

Whenever you want to write a person’s nickname along with their full name, the nickname should be enclosed in quotation marks.

Colons :

The colon is a useful little punctuation mark that can be placed at the end of a sentence to let the reader know that more is coming. You might look at them as a punctuation mark that says, “That thing I just mentioned? Let me tell you more about it.” Here’s a list of the common uses of the colon:

To introduce lists, examples, or explanations

There are times when, in one of your sentences, you might mention something that needs an explanation, an example, or additional information. At the end of that sentence, put a colon to tell the reader that you’re going to provide them with an explanation, an example, or a list that clarifies what you said earlier.

In this example, the writer mentions “a number of things” in the sentence but doesn’t say what they are. The colon at the end of the sentence tells the reader that more information is coming that will explain or expand on what was said before. What comes after the colon, then, must provide the explanation or expansion that was promised.

To introduce a quote

Earlier, we looked at introducing a quote using the speaker’s name and a verb of speech, followed by a comma. Another way to introduce a quote is to use a colon just like you would to introduce a list.

With certain numbers

There are a couple of types of numbers that need colons in them to be correctly written: times and ratios.

Between titles and subtitles

Some titles are a bit long. Some are even longer than that. And some have subtitles, which are a kind of secondary title that goes under^[21] the main title on the cover. When you write a title that has a subtitle, you put a colon between the main title and the subtitle.

Semicolons ;

The semicolon is a poor little punctuation mark that is misunderstood and frequently misused. Some people even make fun of it without ever really trying to understand it. There are only a couple of very specific ways to use a semicolon, and really, if you wanted to, you could avoid using one for your entire life. However, if you’d like to get to know this sleek little mark and when you can toss one into your writing, here is when to do it.

To join two closely-related independent clauses

An independent clause is, as we’ve discussed, basically a sentence that is complete and can stand on its own. When you have two independent clauses that express ideas that are closely related to each other, you can join them together using a semicolon.

Here, the semicolon shows the reader that the second idea is closely related to the first. Using a period instead of a semicolon feels a little too divisive, separating them with a hard stop before the next idea begins. You definitely can’t use a comma here because that would create a comma splice,^[23] where one complete sentence is connected to another complete sentence with just a comma,^[24] and you also wouldn’t want to use a coordinating conjunction^[25] here, either, because you need to put a comma before one of those, not a semicolon.

However, you can use a semicolon before a conjunctive adverb,^[26] such as “however,” “nevertheless,” “moreover,” or “also.” In the previous example, we could’ve used “however” between the two clauses, like this:

After a semicolon, use a lowercase letter unless, of course, the word requires a capital letter, like someone’s name, a day of the week, or a place.

To join items in a list that have their own punctuation

As we discussed earlier, when you write a series of three or more items in a list, you separate those items with commas. However, if an item in the list has a comma that is a part of that item, then you can use semicolons to separate the items in the list to remove any confusion or ambiguity.

In this example, the second item in the list included a comma. If we had used commas to separate the three items in that list, then the comma in the second item might have been misinterpreted by the reader as splitting the second item into two separate items. So, to keep things clear and unambiguous, we use semicolons to separate list items that have their own commas in them. Here’s one more example:

Because each city needed a comma before its corresponding state or country, semicolons were used to separate the individual items in the list of cities.

Ellipses . . .

The ellipsis is more commonly known as, well, the “dot dot dot.” The three periods, separated by spaces in most major writing styles, are collectively called an “ellipsis.”^[27] It has one major use in academic writing and a very different use in more informal or conversational writing, so let’s make sure we’ve got it straight.

To show that something has been omitted from a direct quote

In academic writing, when you use someone else’s words in your text, you might not need to use every word that they wrote. It’s perfectly acceptable to leave out the part that doesn’t relate to your readers, but you still need to tell them that you left a part of the original words out. That’s what an ellipsis does.

In this example, the student wanted to use the description of the Guide, but the original text also mentions a terrible catastrophe that doesn’t make sense in the student’s writing. To avoid confusing the reader, the author removed that reference and replaced it with an ellipsis.

One thing to keep in mind with an ellipsis is that, if you remove a complete sentence from the original quote, you need to make sure you end the sentence before the omission with a period before inserting the ellipsis. It ends up looking like there are four periods together instead of three, but the first period is actually just the end of the previous sentence. Here’s what that can look like:

The sentence that was removed from the original text didn’t really relate to the student’s writing, so it was cut out. The sentence before the omission had ended, so a period was used, but then an ellipsis was inserted to show the reader that a portion of the original text had been removed.

When you remove text from a quote and replace it with an ellipsis, it’s important that you make sure that the text that is left makes sense grammatically and does not change the meaning of the original. For example, the following is an example of what not to do with an ellipsis:

Here, the student clearly butchered the original author’s meaning and intention. The original text describes the Vogons in entirely negative terms, but the student’s quote makes it sound like he was a fan of them because of the way that the original text was cut up and because of what was left out. Don’t do this—it represents a serious breach of academic integrity along with a serious lack of reading comprehension.

To indicate a pause or an unfinished thought

In conversational or informal writing, writers often use an ellipsis when someone pauses during a conversation or to show that they trailed off and didn’t finish their thought.

It can also be inserted at the beginning of a piece of dialogue to indicate that the conversation had been going on previously and that the reader was just joining in and would need to figure it out on the fly.

Just one final reminder—this is a more informal or conversational use of the ellipsis. If you’re writing a more formal or academic paper, stick to the previous usage to avoid any possible confusion.