Have you ever heard of ordinal numbers?

In mathematics, ordinal numbers indicate the rank or position of objects or people. Positioning or ranking numbers may also be used to describe these numbers.

Various parameters are used to determine the sequence of ordinal numbers, including weight, height, marks, size, and other parameters. Ordinals are numbers with such characteristics.

21th or 21st are the numbers belonging to this ordinal series.

The main difference between the 21st and 21th is that the former is correct while the latter is not correct in usage. Apart from that, 21th is the adjective-based form of the number 21, while the 21st is its ordinal form.

*If you are ready to explore the number ladder, let’s dive into the details of this topic.*

## Where Can You Use The Word 21th?

**21th can be used as an adjective meaning “21st in order, position, or rank.” **

For example, you might say that someone is the 21th president of the United States.

21th can also be used as a noun meaning “the 21st day of a month.” For example, January 21th is the 21th day of the year.

However, it’s unconventional to use this form in English language. You’ll never see anyone using this term in English literature or conversation.

## Where Can You Use The Word 21st?

21st is the ordinal form of the number twenty-one. 21st indicates the position or order of something in a sequence.

For example,

- We are living in the
**21st**century. This example indicates the number of the century we are living in right now. - You might also say, “The
**21st**president was James K. Polk.” The word 21st is used to indicate his place in the presidential line of succession.

## Differences Between The Words 21th And 21st

The major difference between both words is that 21st is correct with respect to rules of ordinal numbers whereas 21th is incorrect.

Moreover, The 21st of something is always written as “21st” with a space and the number 21 followed by the letter s. This rule applies regardless of how the date is being used, whether it’s for a birthday, an anniversary, or any other occasion.

The 21th of something, on the other hand, is a typo. The word “twenty-first” is only ever spelled with a space between the number 21 and the letter s. So if you see 21th, it’s incorrect. It’s against the rules of ordinal numbers.

When writing dates, there is often some confusion about whether to use the 21st or 21th. While both are technically correct, 21st is the more commonly used form. 21th is generally only seen in formal or technical contexts. If you are unsure which to use, 21st is the safest choice.

## What Are The Rules For Ordinal Numbers?

**An ordinal number or ordinal is written using numerals as prefixes and adjectives as suffixes. An ordinal number will tell you about the sequence or positioning of the object.**

Examples of ordinal numbers are; 1st, 2nd, 3rd, 4th, 5th, and so on.

*Here is a table for ordinal forms of numbers from one to nine.*

Numbers | Ordinal Form | Written Ordinal Form |

1 | First | 1st |

2 | Second | 2nd |

3 | Third | 3rd |

4 | Fourth | 4th |

5 | Fifth | 5th |

6 | Sixth | 6th |

7 | Seventh | 7th |

8 | Eighth | 8th |

9 | Ninth | 9th |

10 | Tenth | 10th |

*Ordinal form of numbers*

### Unconventional Ordinal Numbers

Almost all ordinal numbers are made by adding the suffix “-th” to the numeral except those ending with 1s, 2s, and 3s. The first three have already been mentioned in the table.

Now, let’s discuss a few more:

**11**: 11th: Eleventh**12**: 12th: Twelfth**13**: 13th: Thirteenth**21**: 21st: Twenty-First**22**: 22nd: Twenty-Second**23**: 23rd: Twenty-Third

And all the upcoming numbers ending with 1, 2, or 3 will follow the same rule as 21, 22, and 23.

## What Is The Point In Using Suffix “-st” And “-th”?

**In English, the suffixes “-st” and “-th” denote ordinality or the position of something in a series.**

For example, the first item in a series would be denoted with the suffix “-st,” as in “1st.”

The ordinal suffixes are also used with days of the month, such as “Wednesday the 3rd.” In addition, the suffixes are used to indicate century number, as in “the 21st century.”

The main difference between the two suffixes is that “-st” is used with numbers that end in 1, 2, or 3, while “-th” is used with numbers that end in any other digit; however, there are some exceptions to this rule. For example, the number 11 is always written as “11th,” regardless of its position in a series.

In general, the rule holds: if a number ends in 1, 2, or 3, it will take the suffix “-st,” while all other numbers will take the suffix “-th.”

## Which One Is Correct: 21th Or 21st?

**The word 21st is correct regarding the conversion rules of ordinal numbers.**

The addition of “-th” at the end of the number “one” is pretty unconventional.

As the number “one” is written as “first” in ordinal form, when you’ll add a numeral to it, it’ll become “1st,” not “1th”. The same rule will apply when writing the numeral word “21st.”

## Final Thoughts

- The difference between 21th and 21st is pretty straightforward.
- 21st is the correct ordinal form of twenty-first, while 21th is incorrect and unconventional.
- Only a person unfamiliar with the English language will use the ordinal form of twenty-one as 21th.
- Not all ordinal numbers follow the same rule.
- Ordinal numbers of numerals ending with 1, 2, and 3 differ from all other ordinal numbers.

*I hope this blog post has helped clear your doubts regarding these two words.*