Is “parenthesis” singular or plural?
- Parenthesis is singular.
- Parentheses (pronounced par-en-thuh-sees) is the plural of parenthesis.
Why does the word parenthesis modify the way it does from singular to plural? Keep reading.
What the definition of parenthesis/parentheses?
The Merriam-Webster defines parenthesis as “an amplifying (see AMPLIFY sense 1) or explanatory word, phrase, or sentence inserted in a passage from which it is usually set off by punctuation.”
What’s the plural of parenthesis?
The plural of parenthesis (parentheses), is irregular. Though it ends in –es as a plural, it does so by replacing its ending in the singular case. Usually, nouns add on the -es/-s to show a plural: books, phones, dogs and cats simply add the s to demonstrate more than one. This is an easy, simple and straightforward way to form a plural noun: just add the s.
This does not work with words like thesis, synopsis, crisis, oasis, (the list goes on.) All of these words derive from Greek, so it may have something to do with the common origin that makes these nouns irregular in their plural forms. See the chart:
Nouns that end in -sis/-ses
| Singular | Plural |
|---|---|
| analysis | analyses |
| crisis | crises |
| diagnosis | diagnoses |
| prognosis | prognoses |
Examples: parenthesis and parentheses
| Form | Example Sentences |
|---|---|
| Singular (parenthesis) |
• The 'Copy' tool action script has has been corrected to add the missing right parenthesis. • If the parenthesis is taken away, the passage would still be complete without it—it's an afterthought or bonus. • If the string begins with an open parenthesis, it is treated as a standard format string. |
| Plural (parentheses) |
• The speaker inserted some often amusing parentheses during his speech. • The percentage of each activity is given in parentheses for comparison. • Parentheses are a popular way to add information to a sentence without breaking its flow. |
Origin of the word parenthesis
From OED on parenthesis:
From Greek parenthesis, literally “a putting in beside,” from parentithenai “put in beside,” from para- “beside”.
Worksheet: English Greek nouns
What is the singular form of “parentheses”?
What is the correct plural of “parenthesis”?
According to the blog post, which of these sentences uses the term incorrectly?
According to the blog, singular words ending in -is, like ‘parenthesis’ and ‘crisis’, often form their plural by changing -is to what?
How is the plural form “parentheses” pronounced, according to the blog?
The author placed an extra note inside a single .
Make sure to use to set off the supplementary information.
The math problem had several sets of .
The chart shows that the plural of “thesis” is .
Words like “parenthesis” and “crisis” are considered irregular because their plural form doesn’t simply add an .
FAQs
Is “parenthesis” singular or plural?
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What’s the plural of parenthesis?
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How do I spell the plural form?
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Give an example of using “parentheses”.
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Give an example of using “parenthesis”.
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Sources
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OED, Origin of parenthesis.
Yash, D. "How to Use Parenthesis Plural (Explained, With Examples)." Grammarflex, Sep 15, 2025, https://grammarflex.com/parenthesis-plural/.
