Ordinal numbers

Ordinal numbers or Ordinal numeral are words representing position or rank in a sequential order; the order may be of size, importance, chronology, and so on.

In English, when referring to the day of the month, cardinal numbers (1, 2, 3, etc.) are converted to ordinal numbers by adding a suffix to indicate their position in the sequence. The suffixes used are -st, -nd, -rd, and -th, and they follow these rules:

• 1st: For days ending in 1, except when the day is 11. Examples: 1st (first), 21st (twenty-first), 31st (thirty-first).
• 2nd: For days ending in 2, except when the day is 12. Examples: 2nd (second), 22nd (twenty-second).
• 3rd: For days ending in 3, except when the day is 13. Examples: 3rd (third), 23rd (twenty-third).
• th: For all other days, including days ending in 0, 4, 5, 6, 7, 8, 9, and the teens (11, 12, 13). Examples: 4th (fourth), 11th (eleventh), 15th (fifteenth), 30th (thirtieth).

Summary of Suffix Rules:

• -st: Days ending in 1 (1, 21, 31), except 11.
• -nd: Days ending in 2 (2, 22), except 12.
• -rd: Days ending in 3 (3, 23), except 13.
• -th: All other days (4–10, 11–20, 24–30).

Example Usage:

• January 1 is written as "January 1st" and spoken as "January first."
• February 22 is written as "February 22nd" and spoken as "February twenty-second."
• March 13 is written as "March 13th" and spoken as "March thirteenth."

This system applies consistently for days 1 through 31 in written and spoken English, with the suffixes reflecting the ordinal nature of the day within the month.