21st century or 21th century

Discussion in 'English Only' started by threethree, Aug 25, 2015.

  1. threethree

    threethree Member

    I was told that both "21st century" and "21th century" were common expressions, but I don't think the latter is grammatically correct. Is it okay to use that in written or oral English?
  2. JulianStuart

    JulianStuart Senior Member

    Sonoma County CA
    English (UK then US)
    You were misinformed.

    21th is incorrect.

    The -st of 1st, 21st, etc represents the end of the word first.
  3. GJones Senior Member

    English - United States
    "21th" shows up in some published books, but it's very rare (ngram). As JulianStuart points out, it stands for a word that ends in "first", so using "th" instead of "st" doesn't make sense.
  4. natkretep

    natkretep Moderato con anima (English Only)

    English (Singapore/UK), basic Chinese
    I would say that 21th is an error. I have done this myself when I edit dates, say from '25th' and then forget to change the ending. The digit 1 in its ordinal form is always first, except the mathematical expressions lie (n + 1)th.

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