In some science and engineering literature, it is common to right the ordinal form of an unknown number m as mth. While the ordinal form of number 1 is first, it is also commonly written as 1st. I was wondering what would be the most appropriate way to write the ordinal form of (m-1)? (m-1)th or (m-1)st?

  • 1
    Could "second-to-last" work? Even if you don't know the exact number of items, it unambiguously means "the one before the last", so if "last" were the Nth item, "second-to-last" would be the (N-1)th. – Friendly Neighborhood Demon Mar 4 '20 at 22:59

(m-1)th is still appropriate. The expression in parentheses will still be read without the ordinal, so consider how it sounds when spoken—em-minus-oneth makes more sense than em-minus-onest.

I should also note that it's common to avoid the problem entirely through rephrasing (e.g. 'the value at index (m-1)'), but that may not be applicable to your field.

  • 1
    I was reading it as em-minus-first. – Blade Mar 3 '20 at 23:40
  • 3
    @Blade While it may vary from person to person (software dev myself), em-minus-first sounds to me like the mth value minus the first value, rather than the value at m-1. – AmaiKotori Mar 3 '20 at 23:50
  • Yeah, I would probably say em-minus-first, with the stress somehow avoiding any possible confusion, in which case I would write (m-1)st, if I had to - although I don't think I've ever actually written that, because as @AmaiKotori says, it's often easier to rephrase. But I would have no problem with someone saying em-minus-oneth and writing (m-1)th - I think it's just personal preference :) – DM_with_secrets May 2 '20 at 8:33

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.