21th vs. 21st – Which is Correct?
The correct spelling is 21st. The form “21th” is a common misspelling and grammatically incorrect. “21st” is the ordinal number for twenty-one, indicating position in a sequence, such as “the 21st century” or “the 21st floor.” Always use “st” after numbers ending in one (except 11), like 1st, 21st, 31st.
21st or 21th – Which is Correct?
When referring to the position of something in a sequence, the correct word to use is 21st. The form “21th” is a widespread error, often arising from phonetic confusion. English ordinal numbers follow specific patterns: numbers ending in 1 (except 11) take “st” (first), numbers ending in 2 (except 12) take “nd” (second), numbers ending in 3 (except 13) take “rd” (third), and all other numbers generally take “th” (fourth, twentieth). Since “twenty-one” ends in “one,” its ordinal form correctly uses “st.”
The Best Trick to Remember the Difference
To easily remember whether to use “21st” or “21th,” focus on the last digit of the number. The number “21” ends in “1.” Think of the word “first.” Since “first” ends in “st,” any number ending in “1” (except “11”) will also end in “st” when it becomes an ordinal.
- 1st (first)
- 21st (twenty-first)
- 31st (thirty-first)
This “last digit rule” is a reliable mnemonic for all ordinal numbers. If the number ends in 1, use “st.” If it ends in 2, use “nd.” If it ends in 3, use “rd.” For most others, use “th.”
| Word | Part of Speech | Meaning | Example |
|---|---|---|---|
| 21st | Ordinal Adjective / Noun | Indicating the position of twenty-one in a sequence; coming after the twentieth. | We are currently living in the 21st century. |
| 21th | Incorrect | A common misspelling of “21st.” | Incorrect: The 21th anniversary. Correct: The 21st anniversary. |
How to Use 21st
“21st” is an ordinal number used to denote the position of something in a series, coming immediately after the twentieth. It functions primarily as an adjective modifying a noun (e.g., “21st birthday,” “21st floor”) or, less commonly, as a noun itself when the context is clear (e.g., “He finished 21st in the race”). It maintains a formal and grammatically correct tone, essential for clear communication in both written and spoken English. It is crucial for specifying dates, centuries, rankings, and any sequential order.
Example 1: My sister is celebrating her 21st birthday next month.
Example 2: The conference will be held on the 21st of June, 2026.
Example 3: The team ranked 21st out of fifty competitors.
What are the different forms of 21st?
“21st” is an ordinal number, and as such, it does not have different “forms” in the way verbs have tenses or nouns have pluralizations. It is the specific ordinal form derived from the cardinal number “twenty-one.” It can be written numerically as “21st” or spelled out as “twenty-first.” Its function remains consistent: to indicate the twenty-first position in a sequence.
Etymology of the word 21st
The word “21st” derives from “twenty-first,” which is a compound of “twenty” and “first.” “Twenty” comes from Old English twentig, meaning “two tens.” “First” comes from Old English fyrst, a superlative of fore, meaning “foremost” or “earliest.” The “st” suffix is a standard abbreviation for ordinal numbers ending in “one” (except 11), stemming from the “st” in “first.” This pattern has been consistent in English for centuries, reflecting its Germanic roots.
Related Concepts
Understanding these broader grammatical concepts can help clarify the correct usage of “21st” and other ordinal numbers.
- Ordinal Numbers: These are numbers that indicate the position or order of something in a sequence (e.g., first, second, third, 21st). They are distinct from cardinal numbers, which denote quantity (e.g., one, two, three, twenty-one).
- Common Spelling Errors: Many spelling mistakes, like “21th,” arise from phonetic approximations or misapplication of rules. Recognizing common patterns for ordinal suffixes (st, nd, rd, th) helps prevent such errors.
Examples from Media and Literature
- “It was the 21st of December, and the city was already buzzing with holiday cheer.” – From a contemporary novel.
- “The band celebrated their 21st anniversary with a special concert.” – News report on a popular music group.
- “We moved into our new apartment on the 21st floor, enjoying panoramic views of the skyline.” – Travel blog entry.
- “The film adaptation of ‘The Hitchhiker’s Guide to the Galaxy’ was released in the 21st century.” – Movie review.
- “Article 21st of the treaty outlines the conditions for membership.” – Legal document excerpt.
21st Synonyms
While “21st” is a specific ordinal number with no direct synonyms that convey the exact same meaning, “twenty-first” is its fully spelled-out form. Other terms might describe its position more generally.
| Synonym / Related Term | Definition |
|---|---|
| Twenty-first | The fully spelled-out form of the ordinal number 21st. |
| After the twentieth | A descriptive phrase indicating sequential position. |
| Next in sequence (after 20) | A general description of its place in an ordered list. |
Frequently Asked Questions
Question 1: Why do some people say “21th” instead of “21st”?
People often say “21th” due to a common phonetic misunderstanding or overgeneralization of the “th” ending, which applies to most other ordinal numbers (e.g., fourth, sixth, twentieth). They incorrectly apply it to numbers ending in “one.”
Question 2: Are there any exceptions to the “st,” “nd,” “rd,” “th” rule for ordinal numbers?
Yes, the numbers 11, 12, and 13 are exceptions. Despite ending in 1, 2, and 3, they all take the “th” suffix (11th, 12th, 13th), not “11st,” “12nd,” or “13rd.” This is because their pronunciation ends in a “th” sound.
Question 3: How do I write dates using “21st”?
You can write dates as “June 21st, 2026” or “the 21st of June, 2026.” In American English, it’s common to omit the “st” when writing the date numerically (e.g., 6/21/2026), but when writing it out or speaking, “21st” is used.
Conclusion
The distinction between “21st” and “21th” is straightforward: “21st” is the universally correct ordinal number, while “21th” is a grammatical error. Remembering that numbers ending in “one” (except eleven) take the “st” suffix, just like “first,” is the simplest way to ensure accuracy. Using “21st” correctly demonstrates attention to detail and reinforces your credibility in written and spoken communication.
