The Grammar of Ordinal Numbers: A Comprehensive Guide to English Suffixes

The correct use of ordinal numbers is a cornerstone of clear and professional communication in English. These numbers, which indicate position or order in a series (e.g., first, second, third), follow specific grammatical rules for their formation and abbreviation. A frequent point of confusion, particularly for non-native speakers, revolves around numbers ending in zero, such as the 30th day of a month. This article provides a detailed exploration of ordinal numbers, drawing from established linguistic rules and common usage to clarify their proper application. It will examine the fundamental principles governing ordinal suffixes, provide extensive lists and examples for numbers from 1st to 100th, and address common mistakes to ensure accurate and confident usage in both written and spoken English.

Understanding Ordinal Numbers and Their Suffixes

Ordinal numbers are a class of numbers that denote the rank, position, or order of an item within a sequence. They are the linguistic counterpart to cardinal numbers, which express quantity (e.g., one, two, three). The transformation from a cardinal to an ordinal number typically involves adding a specific suffix to the base number. The choice of suffix is not arbitrary; it is dictated by the final digit of the number, a rule that applies consistently across most of the English numbering system.

The primary suffixes used are -st (for numbers ending in 1, except 11), -nd (for numbers ending in 2, except 12), -rd (for numbers ending in 3, except 13), and -th (for all other numbers, including those ending in 0, 4, 5, 6, 7, 8, 9, and the teens 11-13). This system ensures a logical and predictable pattern, though the existence of irregular forms like "first," "second," and "third" requires initial memorization.

The suffix is determined solely by the last digit of the number. For example, the number 21 ends in 1, so it becomes 21st (twenty-first). The number 22 ends in 2, so it becomes 22nd (twenty-second). The number 23 ends in 3, so it becomes 23rd (twenty-third). However, for numbers 11, 12, and 13, the suffix reverts to -th because they are considered a single lexical unit in English: eleventh, twelfth, thirteenth. This exception is crucial to remember, as it breaks the simple digit-based rule for these specific numbers.

The Specific Case of Numbers Ending in Zero

A particularly common source of error is the formation of ordinal numbers for multiples of ten, such as 20, 30, 40, and beyond. The correct suffix for these numbers is always -th. This is because the final digit is zero, which falls under the "other digits" category that takes the -th suffix. The internal vowel often changes as well, following a historical pattern of vowel reduction.

For instance, the cardinal number "thirty" (30) becomes the ordinal "thirtieth" (30th). The "y" in "thirty" is replaced by "ie" before adding the suffix, a transformation that also occurs for other tens (e.g., twenty → twentieth, forty → fortieth, fifty → fiftieth). The incorrect form "30rd" is grammatically impossible, as the suffix -rd is reserved exclusively for numbers ending in the digit 3, with the exception of the teen number 13 (which uses -th). Applying -rd to a number ending in zero violates the established grammatical rules of English and can lead to confusion and a perception of poor literacy.

This rule is particularly important when writing dates. When referring to the 30th day of a month, the correct form is "the 30th of June," not "the 30rd of June." The pronunciation also aligns with this rule: "thirtieth" is pronounced with a clear "th" sound at the end, distinct from the "rd" sound in "thirty-third." Understanding this distinction is essential for accurate communication in professional, academic, and everyday contexts.

Comprehensive Guide to Ordinal Numbers from 1st to 100th

To master the use of ordinal numbers, a thorough review of the system from 1st to 100th is invaluable. The following tables and lists provide a structured reference, highlighting the patterns, exceptions, and correct suffixes for each number range.

Ordinal Numbers 1–20

The first twenty ordinal numbers contain the most irregular forms and the critical exceptions for the teens. Memorizing this initial set establishes a strong foundation for understanding the broader system.

Ordinal Numbers 21–30

This range demonstrates the application of the basic suffix rule (based on the last digit) for numbers beyond the teens. Note the vowel change for "twenty" to "twentieth."

Ordinal Numbers 31–40

Continuing the pattern, the numbers 31, 32, and 33 follow the standard suffix rules, while 34-39 and 40 all take the -th suffix. The number 40, like 30, undergoes a vowel change from "forty" to "fortieth."

Ordinal Numbers 41–50

This range solidifies the pattern. The numbers 41, 42, and 43 use -st, -nd, and -rd respectively, while 44-49 and 50 all use -th. The number 50, "fifty," becomes "fiftieth."

Ordinal Numbers 51–60

The pattern remains consistent through the 50s and 60s. The numbers 51, 52, and 53 are formed with their respective suffixes, and 54-59 and 60 all take -th. The number 60, "sixty," becomes "sixtieth."

Ordinal Numbers 61–70

As we move further, the rules are applied without exception. The numbers 61, 62, and 63 follow the standard suffix pattern, while 64-69 and 70 all use -th. The number 70, "seventy," becomes "seventieth."

Ordinal Numbers 71–80

The 70s and 80s continue the established pattern. The numbers 71, 72, and 73 are formed correctly, and 74-79 and 80 all take -th. The number 80, "eighty," becomes "eightieth."

Ordinal Numbers 81–90

In the 80s, the numbers 81, 82, and 83 use -st, -nd, and -rd, while 84-89 and 90 all use -th. The number 90, "ninety," becomes "ninetieth."

Ordinal Numbers 91–100

The final decade in this range, 91-100, perfectly illustrates the rule. The numbers 91, 92, and 93 are formed with their specific suffixes, while 94-99 and 100 all take -th. The number 100, "one hundred," becomes "one hundredth."

Common Mistakes and How to Avoid Them

Even with a clear understanding of the rules, mistakes can occur due to oversight or the influence of similar-sounding numbers. Here are the most common errors and strategies to avoid them.

1. Using "30rd" or "40rd": As discussed, this is the most frequent error for numbers ending in zero. The correct forms are "30th" (thirtieth) and "40th" (fortieth). Remember, the suffix is based on the last digit. A zero takes -th.
2. Confusing Teen Numbers: The numbers 11, 12, and 13 are the only ones in the teens that do not follow the simple digit-based suffix rule. They are "eleventh," "twelfth," and "thirteenth," not "oneth," "twoth," or "threeth." This is an irregularity that must be memorized.
3. Forgetting Vowel Changes: For numbers ending in "y" (like 20, 30, 40, etc.), the "y" changes to "ie" before adding -th. Writing "twentyth" or "threetyth" is incorrect. The correct forms are "twentieth," "thirtieth," etc.
4. Overgeneralizing Suffix Rules: Applying the -st, -nd, or -rd suffix to numbers where it doesn't belong (e.g., "21th" instead of "21st") is a common mistake. Always check the last digit and remember the teen exceptions.
5. Incorrect Abbreviations: In writing, the abbreviations (1st, 2nd, 3rd, 4th, etc.) must be used correctly. Writing "1th," "2th," or "3th" is grammatically incorrect. The abbreviation should match the written-out form.

To avoid these mistakes, a good practice is to mentally check the last digit of the number before choosing a suffix. For numbers ending in 1, 2, or 3, confirm they are not 11, 12, or 13. For all other cases, use -th. When in doubt, writing the number out in full (e.g., "thirty-first" instead of "31st") can help confirm the correct abbreviation.

Practical Applications in Writing and Speech

The correct use of ordinal numbers is essential in numerous contexts. In date writing, it is fundamental for clarity (e.g., "the 30th of June," "May 21st"). In academic and professional writing, ordinal numbers are used for citations (e.g., "see chapter 5th"), rankings (e.g., "she finished in 3rd place"), and enumerating points in a list (e.g., "firstly," "secondly," "thirdly"). In everyday communication, they are used for anniversaries (e.g., "our 25th anniversary"), birthdays (e.g., "her 30th birthday"), and event scheduling (e.g., "the meeting is on the 10th").

Using the correct form enhances the professionalism and clarity of your communication. Incorrect usage can distract the reader or listener and may lead to misunderstandings, especially in formal or time-sensitive contexts. For example, an invitation stating "the 30rd of the month" would be immediately noticeable as an error and could undermine the sender's credibility.

Conclusion

Mastering the grammar of ordinal numbers is a valuable skill that contributes to effective and precise English communication. The system, while having a few exceptions, is largely logical and rule-based, with the suffix determined by the last digit of the number. The key takeaways are that numbers ending in 1, 2, and 3 (except for 11, 12, and 13) take -st, -nd, and -rd respectively, while all other numbers, including those ending in 0, 4, 5, 6, 7, 8, 9, and the teens 11-13, take -th. For multiples of ten, a vowel change from "y" to "ie" occurs before the -th suffix is added. By internalizing these rules and practicing their application, one can confidently navigate dates, rankings, and sequences, ensuring that written and spoken English is both correct and polished. The consistent application of these principles is a hallmark of attention to detail and linguistic competence.

Sources

1. 30rd or 30th?
2. Do we say 30th or 30st?
3. 30th or 30rd?
4. Ordinal Numbers in English
5. Cardinal and Ordinal Numbers Chart