The correct way to write the ordinal number for “21” is “21st”, not “21th”. This is because when we use ordinal numbers, we typically add the suffix “-th” to the end of the cardinal number to indicate a specific position in a sequence. However, there are a few exceptions to this rule, and “21” is one of them.
In English, the ordinal numbers from 4 onwards do not follow the standard pattern of adding “-th” to the end of the cardinal number. Instead, they have their own unique forms. For example, we write “fourth” for the ordinal form of “4”, “fifth” for “5”, “sixth” for “6”, and so on. These exceptions also include the numbers ending in “1” such as “first”, “eleventh”, and indeed “twenty-first”.
The reason for this irregularity lies in the historical development of the English language. Old English, the predecessor of Modern English, used to have a system where “-teogotha” was added to the end of the cardinal numbers to create ordinals. Over time, this ending was shortened to “-th” and became the standard for most ordinal numbers. However, some numbers, particularly those ending in “1”, retained the older form, giving us words like “first” and “twenty-first.”
Let’s look at some examples to highlight the correct usage:
– My birthday is on the 21st of May.
– He was the 21st person to cross the finish line.
– We celebrated our 21st wedding anniversary last week.
– The 21st century has seen significant technological advancements.
As you can see, the correct use of “21st” is consistent with the usual practice of forming ordinal numbers. It may seem unusual at first, especially when compared to the more common “th” suffix, but it follows the established patterns of the English language.
To summarize, “21st” is the correct way to write the ordinal form of “21”. Though it may not fit the standard rule of adding “-th” to the end of a cardinal number, it aligns with the exceptions in the English language for numbers ending in “1”. So, the next time you encounter the need to express the position of “21” in a sequence, remember to use “21st” and not “21th”.