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Parenthesis or Parentheses: Differences and Correct Usage

As we write, we sometimes find it necessary to add a little more context for the reader. Parenthetical comments are a common way to add a brief aside or more than one aside, but what do we call this? Is it “parenthesis” or “parentheses”?

The main difference between “parenthesis” and “parentheses” is that of the singular and plural forms. We’re most likely to see and use the plural form, as parentheses () are punctuation marks we use to interrupt a sentence by adding explanatory information. We can also refer to the explanatory information itself as a parenthesis.

This article will explore the difference between the singular and plural forms of “parenthesis,” the purpose of parentheses, and how to use both terms correctly. 

Is Parentheses Singular or Plural?

Most often, the word “parenthesis” indicates one of a pair of punctuation marks known together as “parentheses.” Parentheses look like this: ( ). We can refer to either one of these curved marks as a parenthesis, and as a pair, we refer to them as parentheses in American English, while British English refers to them as round brackets.

However, we can also refer to the information enclosed within those punctuation marks as a “parenthesis.” If you have more than one such parenthetical expression, you have parentheses. A parenthesis amplifies or explains something while interrupting the normal flow of the sentence (source). 

What Are Parentheses?

A parenthesis is a parenthetical expression. We use parentheses in English to add information explaining something or supplementing an idea in a sentence. Since they tend to interrupt the flow of the sentence, synonyms for a parenthesis include divergence, interlude, or aside (source).

We can even apply it to mean something that interrupted the normal flow of something else, like your life. Merriam-Webster provides the example of war acting as a parenthesis of someone’s regular life.

A “parenthesis” can be a single word, a clause, a phrase, or even a complete sentence.

There is a lot of grammatical leeway for writers to use parentheses to add interest, color, and subtle nuances to their writing. It can give your writing a little more pop, and it will always add interesting additional information to a sentence.

However, parentheses can make sentences long and convoluted, and we should, therefore, use them sparingly. 

What Is an Example of a Parenthesis?

When we use a parenthesis or parenthetical comment in a sentence, the key thing to remember is we should be able to remove the parenthetical expression without changing the meaning or grammatical integrity of the sentence in question. Therefore:

My sister (and her dog) is coming to visit me today.

As you can see, you can remove the parenthesis and the surrounding parentheses in bolded text entirely, and the sentence will still read correctly:

My sister is coming to visit me today.

The addition of parentheses in this sentence indicates it is more important to the speaker that her sister is visiting, and the dog is simply an afterthought or aside.

Pay Attention to Verb Conjugation

Should you choose to write the sentence without parentheses, you would need to change the verb “is” to accommodate the additional subject. For example:

My sister and her dog are coming to visit me today.

My sister (and her dog) is coming to visit me today. 

We conjugated the verb for the plural subject “My sister and her dog” when not using a parenthetical comment with punctuation. However, as soon as we add that information as an aside with parentheses, we must conjugate for the singular subject “My sister” instead.

This means that you should pay very careful attention to how you conjugate verbs for either singular or plural subjects. Below, we’ve included a few more examples of correctly and incorrectly conjugating verbs when using parentheses:

This dog (and others like him) always pulls on the lead. This dog (and others like him) always pull on the lead.
My friend (and her mom) likes the new coffee shop. My friend (and her mom) like the new coffee shop. 

Parentheses vs. Round Brackets

We often use the word “parentheses” in its plural form to mean the curved lines that add additional information to a sentence. However, in countries where British English is dominant, the term for this punctuation mark is round or curved brackets. 

In American English, brackets are a completely different form of punctuation, looking like this: [ ]. In contrast, British English refers to these as square brackets (source). 

We similarly use brackets or square brackets to provide additional information, but they more often function as an editor’s comment. For example, we might use them to note odd spelling or missing words in a quote or add context to a sentence as editorial comments.

Parenthetical Comments, Commas, and Em Dashes

ParenthesesCommasEm Dashes
( ), ,—  — or — — 

You can punctuate a parenthetical comment with parentheses, commas, or em dashes, but there is a change in emphasis. Parentheses tend to minimize the importance of the parenthetical comment, while em dashes and commas tend to accentuate them (source).

We expect the president (and his team) at five o’clock.

We expect the president, and his team, at five o’clock.

We expect the president — and his team — at five o’clock.

Unlike em dashes, we can place commas after a parenthetical comment followed by an independent clause.

She arrived home (it was already dark outside), and then she made dinner.

It was a quiet evening after a long day (filled to the brim with activities), and she was tired.

He liked her so much (for her smile and humor), so he immediately asked her out.

I signed up for the trial period of a new app (and enjoyed it tremendously), so I upgraded to Premium.

We use commas to connect compound sentences with more than one independent clause using “for,” “and,” “nor,” “but,” “or,” “yet,” or “so” (FANBOYS).

For more on how to use commas with “so,” make sure you read our article on this topic.

Specialized Functions of Parentheses

Image by Gerd Altmann via Pixabay

There is a certain freedom that writers have when using parentheses because we can utilize them in so many different ways. They can add information, add color and nuance, or simply comment on what the sentence already says.

However, there are certain special cases when the use of parentheses is the rule rather than a choice (source).

Lists and Phone Numbers

If you are listing or numbering something in a sentence, we can place the numbers or letters in parentheses to make it easier to read. For example:

Please add the following three documents to your application: (1) a profile photo, (2) a cover letter, and (3) at least four contactable references.

We usually place area codes of phone numbers in parentheses:

Please get in touch with us by calling our hotline at (212) 555 8910.

Adding Short Bits of Information

We often place time zones as abbreviations in parentheses after the statement of the exact time:

The meeting will take place tomorrow morning at 09:00 (EST).

We always place short translations of foreign words in parentheses:

My knowledge of French is limited to bonjour (hello) and je t’aime (I love you).

Particularly in historical writing, we place a person’s year of birth and year of death in parentheses: 

Lady Diana, Princess of Wales (1961–1997), was one of the most beloved members of the Royal Family.

Explaining Abbreviation or Acronyms

We should always place abbreviations and acronyms, which are shortened forms of words, in parentheses. 

There are two ways in which to do this. Firstly, you can place the abbreviation or acronym in parentheses after writing the word out in full and then refer to it as the abbreviation or acronym for the rest of the document. 

The second way you can use it is first to use the abbreviation and place the description in parentheses should you feel that your readers may not know the meaning of the abbreviation or acronym in question. For example:

Philip Truter is the Chief Financial Officer (CFO) of a very large corporation. He has held the CFO position for a number of years.

A computer needs a lot of RAM (Random Access Memory) for you to be able to play online games.

Using Punctuation Marks with Parentheses

Image by Kelly Sikkema via Unsplash

In English, it is essential to follow specific rules when using punctuation and parentheses. Let’s take a look at some of the most common examples.

Periods and Capitalization

A period is a dot that you put at the end of the sentence, and it is, perhaps, the most common of all punctuation marks and the one that second-language learners tend to learn first. British English refers to this same punctuation mark as the full stop.

When it comes to parentheses and parenthetical content, we can use the period in two ways.

If the content in the parentheses is a complete sentence that stands on its own in a larger chunk of text, we place the full stop inside of the last parenthesis or the last pair of the parentheses. 

Additionally, if a parenthetical sentence stands on its own, we will also capitalize the first word as it would be for an ordinary sentence. For example:

It is possible to eat an entire pizza in one sitting. (Although it wouldn’t be a good idea to do this regularly.) We can also make pizza using gluten-free flour.

If we add the parenthetical content to the end of a longer sentence, we should place the period outside of the last parenthesis. For example:

It is possible to eat an entire pizza in one sitting (although we do not recommend it). 

If the parenthetical content is in the middle of a sentence, it does not receive any capitalization or period. For example:

It is possible to eat an entire pizza in one sitting (although I wouldn’t recommend it) and still have room for dessert. 

Question Marks and Exclamation Marks

We use question marks and exclamation marks fairly often in the English language, and they change the nature of the sentence. Although question marks and exclamation marks always go at the end of a sentence, we can make an exception where it concerns parentheses. This article was written for

When using parentheses, even in the middle of a sentence, the writer can choose to add a question mark or exclamation mark. You will then not capitalize the next word as you may in ordinary writing, as you will remember that the parenthetical content does not change the grammatical structure of the sentence it is in (source). 

She was very smart (and beautiful too!), which is why he liked her so much.

They verified my credentials for the job (why wouldn’t they?), and the company hired me the next day. 

There are numerous punctuation marks in the English language, so it is useful for second-language learners to invest in helpful study aids to understand how they can use them. 

Final Thoughts

The difference between the words “parenthesis” and “parentheses” is that “parentheses” is the plural form while “parenthesis” is the singular. You are most likely to use and hear the word “parentheses” in English when referring to the pair of curved lines we use to set off additional information from the rest of the sentence.

When we do use the term “parenthesis,” it is most often in reference to the parenthetical comment itself or, more broadly, to refer to an interruption in the normal course of events.

The parenthetical content inside the curved lines can often stand on its own and will never interfere with the grammatical structure of the sentence (remember that, and you’re good to go).

Comma After So: When Is It Applicable?

Sunday 30th of May 2021

[…] way you can use a comma is for a parenthesis. A parenthesis is when there is a part of a sentence that interjects extra information. If you […]

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