Have you ever wondered whether the correct word is “parenthesis” or “parentheses”? These two words look almost identical, but they have different meanings based on whether you’re talking about one or more than one. If you’ve ever hesitated before writing one of them, you’re not alone.
Parenthesis is the singular form, meaning one of these curved punctuation marks: ( ). Parentheses is the plural form, meaning two or more of these marks or multiple sets used in writing.
Examples:
- Put the extra information in a parenthesis.
- The sentence contains two sets of parentheses.
The confusion is understandable. People often search for parenthesis or parentheses, parenthesis vs parentheses, is parentheses plural, or what is the plural of parenthesis because the spelling and pronunciation can be tricky. And here’s the kicker: the word parentheses doesn’t simply add an s to parenthesis like many regular plurals.
In this guide, you’ll learn the difference between parenthesis and parentheses, their definitions, pronunciations, plural forms, and correct usage. You’ll also see clear examples of parenthesis in a sentence, learn how to use parentheses correctly, and discover other related punctuation terms so you can use each word with confidence.
Parenthesis or Parentheses at a Glance
The quickest way to remember the difference is to think about one versus more than one.
| Word | Number | What it means | Example |
| Parenthesis | Singular | One parenthesis or a single parenthetical remark | “The opening parenthesis is missing.” |
| Parentheses | Plural | Two or more parentheses | “Put the explanation in parentheses.” |
| **( ** | Singular | Opening parenthesis | “Add an opening parenthesis here.” |
| **) ** | Singular | Closing parenthesis | “Delete the extra closing parenthesis.” |
| ( ) | Plural | The pair of parentheses | “The phrase appears in parentheses.” |
Cambridge lists parentheses as the plural of parenthesis. In US English, parenthesis can also refer to either member of the pair of marks or to the information enclosed by them.
The easiest rule
One parenthesis, two parentheses.
Think of it like this:
one analysis → several analyses
one diagnosis → several diagnoses
one parenthesis → several parentheses
The spelling changes because parenthesis comes from a group of words with Greek derived plural forms. You don’t simply add s to create parenthesises.
What Does Parenthesis Mean?
Parenthesis is a singular noun. It has two closely related uses.
First, it can refer to one of the curved punctuation marks used in writing:
- ( = opening parenthesis
- ) = closing parenthesis
Second, parenthesis can refer to an inserted remark or piece of information that interrupts the main flow of a sentence.
For example:
Maria, (who recently moved to Chicago), joined the meeting.
Here, the words inside the marks form a parenthetical element.
Cambridge also defines parenthesis as a remark added to a sentence to provide extra information or explanation.
Parenthesis as a punctuation mark
When you’re talking about just one mark, use parenthesis.
For example:
- “The opening parenthesis needs to move two spaces to the left.”
- “You forgot the closing parenthesis.”
- “There’s an extra parenthesis at the end of the formula.”
Notice that each sentence discusses one individual mark.
Parenthesis as an inserted remark
The word can also describe an interruption or aside within a larger statement.
For example:
The manager, a former engineer, approved the proposal.
The phrase a former engineer provides additional information. It isn’t essential to the basic sentence:
The manager approved the proposal.
In this broader grammatical sense, a parenthesis isn’t limited to the ( ) symbols. A parenthetical remark can also appear between commas or dashes, depending on the sentence and style.
That’s an important distinction because parenthesis doesn’t always mean the physical punctuation mark itself.
What Does Parentheses Mean?
Parentheses is the plural form of parenthesis.
In everyday US English, people commonly use parentheses to refer to the paired marks:
( )
For example:
Enter your phone number (including the area code).
The words including the area code appear between a pair of parentheses.
Cambridge explicitly identifies parentheses as the plural form of parenthesis.
Why do writers usually say “parentheses”?
Because a normal parenthetical expression uses two marks:
- An opening parenthesis: (
- A closing parenthesis: )
Together, they form a pair:
(extra information)
That’s why you’ll often hear:
- “Put it in parentheses.”
- “The phrase is inside parentheses.”
- “Use parentheses around the abbreviation.”
You aren’t necessarily counting the marks individually. You’re referring to the paired punctuation as a unit.
Is Parenthesis Singular or Plural?
Parenthesis is singular.
Parentheses is plural.
That’s the central answer to the entire question.
Consider these examples:
“There is one parenthesis in this expression.”
“There are two parentheses in this expression.”
The difference becomes especially clear when you talk about unmatched punctuation.
Singular examples
- “The opening parenthesis doesn’t have a match.”
- “Remove the extra parenthesis.”
- “The closing parenthesis is in the wrong place.”
Plural examples
- “The sentence contains several parentheses.”
- “Put the dates in parentheses.”
- “The information appears between parentheses.”
A useful test is to replace the word with one or several.
If you can say one, use parenthesis.
If you can say two, several, or multiple, use parentheses.
What Is the Plural of Parenthesis?
The plural of parenthesis is parentheses.
Not:
- ❌ parenthesises
- ❌ parenthesis
- ❌ parenthesi
Correct:
- ✅ parenthesis
- ✅ parentheses
The spelling follows a pattern found in several English words derived from Greek.
| Singular | Plural |
| parenthesis | parentheses |
| analysis | analyses |
| diagnosis | diagnoses |
| basis | bases |
| thesis | theses |
| hypothesis | hypotheses |
| synthesis | syntheses |
This pattern can feel unusual because English has plenty of ordinary plurals that simply add s. However, parenthesis belongs to a different group.
Parenthesis and parentheses pronunciation
The pronunciation changes slightly between the singular and plural.
Parenthesis: /pəˈrenθəsɪs/
Parentheses: /pəˈrenθəsiːz/
Cambridge gives these pronunciations for US English.
The final sound is the easiest clue:
- parenthesis ends with an “sis” sound.
- parentheses ends with an “seez” sound.
So you can remember:
parenthesis = one
parentheses = more than one
Why Do People Usually Say “Parentheses” for ( )?
Here’s where the confusion starts.
The symbols ( ) contain two separate marks, but people often talk about them as one punctuation pair. In that situation, parentheses is the natural plural term.
For example:
“Put the author’s birth year in parentheses.”
You’re referring to the entire pair:
Jane Austen (1775–1817)
You aren’t talking about only ( or only ).
If you specifically need to identify one mark, however, use the singular:
“The opening parenthesis goes before the year.”
That distinction is particularly useful when proofreading, editing, coding, or debugging text.
Think of parentheses as a container
A simple analogy helps.
Imagine a pair of parentheses as two bookends:
( information )
The left bookend is the opening parenthesis.
The right bookend is the closing parenthesis.
Together, they’re parentheses.
That makes the terminology much easier to visualize.
How to Use Parenthesis in a Sentence
Use parenthesis when you’re referring to one mark or a singular parenthetical element.
Here are some practical examples.
Referring to one punctuation mark
“The opening parenthesis is missing.”
“Delete the extra closing parenthesis.”
“The final parenthesis should appear after the citation.”
“This expression has an unmatched parenthesis.”
Each example discusses an individual mark.
Referring to a single parenthetical remark
The word can also refer to one inserted thought or aside.
For example:
“The sentence contains a parenthesis explaining where the meeting will take place.”
Here, parenthesis refers to the inserted information rather than simply one physical punctuation mark.
Cambridge uses this broader meaning when it describes a parenthesis as a remark added to a sentence for explanation or additional information.
How to Use Parentheses in a Sentence
Use parentheses when referring to the paired punctuation marks or multiple parenthetical elements.
Examples with dates
The company opened its first office in Boston (1998).
Examples with additional information
The conference will take place in Austin (Texas).
Examples with abbreviations
The Federal Bureau of Investigation (FBI) released a statement.
Examples with clarification
Her brother (the older one) lives in Denver.
Examples with numbers
Choose the second option (2).
In each case, the information sits between two marks, so parentheses is the natural term.
Parentheses Can Add Information Without Changing the Main Sentence
One of the most useful things about parentheses is that they let writers insert secondary information without making that information part of the sentence’s central structure.
Consider:
The new restaurant opens next Friday (assuming construction stays on schedule).
Remove the parenthetical material:
The new restaurant opens next Friday.
The main sentence still works.
That’s one reason parentheses are useful. They create a visual boundary around information that matters but isn’t necessarily central to the sentence.
The Chicago Manual of Style treats parentheses as punctuation for related material that is connected to the sentence but isn’t essential to its main construction. Its current style guide has a dedicated section on the use of parentheses, including their interaction with brackets and other punctuation.
Parenthesis or Parentheses: What’s the Difference?
The difference is mainly number, but context determines which form sounds natural.
| If you’re talking about… | Use |
| One mark | parenthesis |
| One opening mark | opening parenthesis |
| One closing mark | closing parenthesis |
| The pair ( ) | parentheses |
| Multiple pairs | parentheses |
| A single parenthetical remark | parenthesis |
| Multiple parenthetical remarks | parentheses |
Compare these sentences
Correct:
“The opening parenthesis is missing.”
Correct:
“The information belongs in parentheses.”
Correct:
“The paragraph contains several parentheses.”
Correct:
“The sentence contains a parenthesis that interrupts the main thought.”
The word changes according to what you’re describing.
Parentheses vs. Brackets
Another common source of confusion involves parentheses and brackets.
In US English, the distinction is generally:
- Parentheses: ( )
- Square brackets: [ ]
- Braces: { }
So if you see:
The answer is (correct).
Those are parentheses.
If you see:
The answer is [correct].
Those are square brackets.
And:
The answer is {correct}.
Those are braces.
However, terminology varies across English varieties. Cambridge notes that brackets can be used for parentheses in British English, while round brackets is another term used for ( ).
Parentheses in US English
For US English writing, parentheses is the standard term for:
( )
For example:
Please enter your date of birth (MM/DD/YYYY).
Brackets in US English
In US English, brackets normally means:
[ ]
For example:
The original quotation reads, “She [the witness] arrived shortly afterward.”
Square brackets often serve a different editorial purpose, particularly when writers add or alter information within quoted material.
Parentheses vs. Parenthetical
The words parentheses and parenthetical are related, but they aren’t interchangeable.
Parentheses is a noun.
Parenthetical is generally an adjective describing something that functions as an aside or appears within parentheses.
Compare:
The explanation appears in parentheses.
The writer added a parenthetical explanation.
The first sentence names the punctuation.
The second describes the explanation.
Cambridge defines parenthetical in connection with information written in parentheses or added as an aside.
A quick comparison
| Word | Part of speech | Example |
| parenthesis | Noun | “Remove the parenthesis.” |
| parentheses | Noun, plural | “Put the dates in parentheses.” |
| parenthetical | Adjective | “The author added a parenthetical remark.” |
You might also encounter parenthetically, an adverb:
“Parenthetically, the author mentions that the building was once a school.”
The family of words is closely connected, but each form has a different grammatical job.
How Parentheses Work With Punctuation
Knowing the singular and plural forms solves the vocabulary problem. However, if you’re writing about parentheses, punctuation placement matters too.
Consider:
The project finished on time (despite several delays).
The period belongs to the main sentence.
If the parenthetical material occurs within a larger sentence, the sentence’s normal ending punctuation generally remains outside the closing parenthesis.
The Chicago Manual of Style explains that when parenthetical material falls within a sentence, the sentence still needs its final punctuation after the closing parenthesis.
Parenthetical material inside a sentence
The team finished the project (despite the delays).
The period comes after the closing parenthesis.
A complete sentence inside parentheses
When an entire independent sentence appears in parentheses, its punctuation can remain inside:
The project finished early. (Everyone was surprised.)
The parenthetical sentence stands on its own.
The key question is simple:
Does the parenthetical material belong to the surrounding sentence, or is it a complete sentence of its own?
That distinction determines where the final punctuation goes.
Parentheses Can Make Writing More Precise
Parentheses aren’t just decorative marks. Used well, they help readers understand how pieces of information relate to one another.
Consider this sentence:
The company hired three specialists (a lawyer, an accountant, and a tax consultant).
The parentheses tell the reader that the material inside them explains the word specialists.
Without them, the relationship becomes less visually obvious:
The company hired three specialists a lawyer, an accountant, and a tax consultant.
The second version needs different punctuation to work properly.
Parentheses provide a clean boundary.
They can clarify abbreviations
The Occupational Safety and Health Administration (OSHA) issued new guidance.
They can clarify locations
The company operates in Portland (Oregon).
They can provide dates
William Shakespeare (1564–1616) wrote many influential plays.
They can add short explanations
The meeting begins at noon (not 1 p.m.).
In each case, the parenthetical information supplements the main statement.
Common Mistakes With Parenthesis and Parentheses
These words cause a handful of predictable errors.
Mistake: Using “parentheses” as a singular noun
Incorrect:
“This parentheses is unnecessary.”
Correct:
“This parenthesis is unnecessary.”
Why? Because you’re talking about one mark.
Mistake: Using “parenthesis” for the pair
Less natural:
“Put the date in parenthesis.”
In US English, the standard expression is:
“Put the date in parentheses.”
That’s because the date is enclosed by a pair of marks.
You may encounter in parenthesis in some varieties or contexts, but in parentheses is the standard US English choice.
Mistake: Writing “parenthesises”
Incorrect:
“The sentence has two parenthesises.”
Correct:
“The sentence has two parentheses.”
The plural doesn’t follow the normal +s pattern.
Mistake: Confusing parentheses with brackets
Incorrect terminology in US English:
“Put the phrase in brackets.”
if you’re specifically referring to:
( )
Better:
“Put the phrase in parentheses.”
If you’re referring to:
[ ]
then brackets is the appropriate term in US English.
Mistake: Forgetting the closing parenthesis
Incorrect:
The conference begins at noon (Friday.
Correct:
The conference begins at noon (Friday).
An unmatched parenthesis can make a sentence look unfinished. In programming, it can even cause an expression or function call to fail.
Parentheses in Formal and Academic Writing
Parentheses appear frequently in academic, technical, and professional writing.
They’re especially useful for information that supports the main point without becoming the main point itself.
Academic example
Researchers examined 250 participants (125 in each group).
The main statement remains clear, while the parenthetical phrase supplies a useful numerical detail.
Professional example
Please submit the invoice by Friday (September 4).
The date clarifies Friday without interrupting the basic instruction.
Technical example
Select the settings icon (⚙) to open the configuration menu.
The symbol provides an additional visual cue.
Citation example
Academic styles also use parentheses for citations.
For example:
The study found a significant relationship between the two variables (Smith, 2025).
The exact citation format depends on the style guide you’re following. APA, MLA, Chicago, and other systems have their own rules.
The important point here is that the punctuation term remains parentheses, even when the marks serve a specialized purpose.
Parentheses in Mathematics and Technical Writing
The word parentheses isn’t limited to ordinary prose.
Mathematics uses parentheses constantly.
For example:
3 × (4 + 2)
Here, the parentheses group 4 + 2 together.
They tell the reader which operation belongs together before multiplication occurs.
Parentheses can also identify function arguments:
f(x)
They can group negative values:
(-5)
They can show intervals in mathematical notation:
(2, 7)
The terminology stays the same.
One mark is a parenthesis. The pair is parentheses.
Technical writing also uses parentheses for variables, units, abbreviations, and supplementary information.
For example:
Temperature was measured in degrees Celsius (°C).
The marks remain parentheses even though the context is technical rather than grammatical.
A Practical Case Study: Fixing a Confusing Sentence
Suppose an editor receives this sentence:
The survey included 500 participants (250 men and 250 women).
At first glance, there’s nothing wrong with it.
Now imagine the editor needs to describe the punctuation itself.
They might write:
“The sentence contains a pair of parentheses.”
That’s correct.
But if one mark disappears during editing:
The survey included 500 participants (250 men and 250 women.
The editor could say:
“The sentence is missing a closing parenthesis.”
That’s also correct.
Notice what changed.
The sentence originally contained two marks, so the editor referred to them collectively as parentheses.
After one mark disappeared, the editor needed to identify one specific mark, so parenthesis became the correct word.
The lesson
The word follows the thing you’re counting.
That’s the simplest way to avoid the mistake.
Parenthesis or Parentheses Examples
The following examples show how the words work in different contexts.
| Example | Correct word | Why |
| “The opening ___ is missing.” | parenthesis | One mark |
| “Put the date in ___.” | parentheses | A pair of marks |
| “The paragraph contains several ___.” | parentheses | More than one |
| “Delete the extra closing ___.” | parenthesis | One mark |
| “The abbreviation appears in ___.” | parentheses | The abbreviation is enclosed by a pair |
| “The sentence contains a ___.” | parenthesis | One parenthetical element |
| “The document uses nested ___.” | parentheses | Multiple paired marks |
| “The closing ___ is misplaced.” | parenthesis | One mark |
More natural examples
The author placed the year in parentheses.
There’s an unmatched parenthesis in the final paragraph.
Several terms appear in parentheses.
Check the opening parenthesis before submitting the code.
The editor removed an unnecessary parenthetical phrase.
These examples cover the most common situations you’ll encounter.
How to Remember Parenthesis vs. Parentheses
You don’t need a complicated memory trick.
Just remember:
Parenthesis = one.
Parentheses = more than one.
Here’s another useful shortcut:
One → parenthesis
“The closing parenthesis is missing.”
Pair → parentheses
“Put the phrase in parentheses.”
Several pairs → parentheses
“The document contains several parentheses.”
If you remember one parenthesis, two parentheses, you’ve solved most usage questions.
Parenthesis or Parentheses: Which One Is Correct?
Both words are correct. The choice depends on whether you’re talking about one or more than one.
Use parenthesis when:
- You mean one punctuation mark.
- You mean one opening mark.
- You mean one closing mark.
- You mean a singular parenthetical remark.
- You’re discussing one specific parenthetical element.
Use parentheses when:
- You mean the pair ( ).
- You mean multiple pairs.
- You’re referring to information enclosed by the pair.
- You’re using the common phrase in parentheses.
Quick decision table
| What you mean | Correct choice |
| One mark | parenthesis |
| The opening mark | parenthesis |
| The closing mark | parenthesis |
| The pair ( ) | parentheses |
| Multiple pairs | parentheses |
| Information inside ( ) | parentheses |
| One inserted remark | parenthesis |
| Multiple inserted remarks | parentheses |
Frequently Asked Questions About Parenthesis or Parentheses
Is it parenthesis or parentheses?
Both are correct, but they aren’t interchangeable.
Parenthesis is singular. Parentheses is plural.
Use parentheses when you’re talking about the pair ( ).
What is the singular of parentheses?
The singular of parentheses is parenthesis.
For example:
one parenthesis
two parentheses
What is the plural of parenthesis?
The plural of parenthesis is parentheses.
Don’t write parenthesises. That’s not the standard English plural.
Is one bracket called a parenthesis?
In US English, an individual curved mark ( or ) is called a parenthesis.
The pair is called parentheses.
The term bracket can mean different things depending on the variety of English and context. In standard US usage, brackets generally refers to square brackets [ ].
Are parentheses and brackets the same thing?
Not usually in US English.
Parentheses: ( )
Brackets: [ ]
However, British English often uses brackets or round brackets for ( ), so terminology can vary between English varieties.
How do you pronounce parenthesis?
In US English, parenthesis is pronounced approximately:
puh REN thuh sis
Its plural, parentheses, ends differently:
puh REN thuh seez
Cambridge gives the US pronunciation as /pəˈrenθəsɪs/ for parenthesis and /pəˈrenθəsiːz/ for parentheses.
Should you say “in parenthesis” or “in parentheses”?
In US English, in parentheses is the standard choice when referring to information enclosed by ( ).
For example:
The author’s birth year appears in parentheses.
The plural makes sense because the information sits between two marks.
Can parenthesis mean something other than punctuation?
Yes.
A parenthesis can also mean an inserted remark or piece of information that interrupts or supplements a sentence. Cambridge recognizes this broader meaning.
For example:
The manager added a parenthesis explaining the decision.
In everyday writing, though, people often use parentheses when they specifically mean the punctuation marks ( ).
Do parentheses always come in pairs?
In ordinary writing, parentheses normally work as a pair because one mark opens the expression and the other closes it.
However, writers may discuss an individual opening or closing mark when editing, proofreading, coding, or describing punctuation.
That’s when the singular parenthesis becomes useful.
Final Answer: Parenthesis or Parentheses?
The difference between parenthesis and parentheses comes down to number.
Parenthesis is singular.
Parentheses is plural.
When you mean one mark, use parenthesis:
“The closing parenthesis is missing.”
When you mean the pair ( ), use parentheses:
“Put the explanation in parentheses.”
When you mean several pairs, use parentheses:
“The document contains several parentheses.”
The same distinction applies when discussing parenthetical remarks. One is a parenthesis. More than one is parentheses.
The rule worth remembering
One parenthesis. Two parentheses.
That’s it. Once you connect the singular form with one mark and the plural form with the pair ( ), the difference becomes much easier to spot.
And if you’re writing in US English, parentheses is the word you’ll most often need when you tell someone to put information inside ( ).
