On another StackExchange QA site, I asked a math question involving Friday 13th. It deals with years having more than one Friday 13th.

I used 'Fridays 13th' as the plural form of 'Friday 13th'. Was I right? Or it should be 'Friday 13ths'? Or even 'Fridays 13ths' (that somehow looks nice to me, but I doubt it is correct)?

My research:

  • Google search for +"fridays the 13th" gives 36.600 results;
  • Google search for +"friday the 13ths" gives 239.000 results.

Examples of reputable internet sites using both versions:

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  • In some instances (such as the quoted news story), Friday the 13th would not have to be pluralized when referring to multiple instances of the day. "Since 1950, returns on Friday the 13th have averaged . . " would be quite correct. Similarly, you would say, returns on the Fourth of July, Groundhog Day, or any other specific day--whether a holiday or any other day with a name--, thus referring to them as singular rather than trying to pluralize them. – GMB Jul 6 '14 at 13:51
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    Suppose you said something about Peter the Great, and somebody asked "Peter the Great of Russia or Peter the Great of Zembla". I think the most likely response would be "I didn't know there were two Peter the Greats". So I'd say "Friday the 13ths". – Peter Shor Jul 6 '14 at 15:05

I would argue that "Friday the 13th" (with the the) is such a common set phrase that it behaves as a syntactic atom, i.e. something that shouldn't be split up by syntactic processes. In my experience, people almost never pause at any point when pronouncing the phrase "Friday the 13th", and it all has one continuous intonational contour.

This is all to back up my intuition that, as a native speaker (of American English), Friday the 13ths is the only plural form I can possibly imagine myself speaking here. It does look a little funny in writing, but so does Fridays the 13th, so I'd go with the more natural spoken form.

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    What would then be the plural of 'Tuesday the 25th'? (since 'Tuesday the 25th' is not a common set phrase) – VividD Jul 6 '14 at 8:11
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    @VividD - I would just say "Tuesdays that fall on the 25th of a month" rather than trying to pluralise that directly. – Martin Smith Jul 6 '14 at 12:03
  • When spoken, "Friday the 13ths" is less ambiguous than "Fridays the 13th" so I'll go with clarity on this one. – James Jul 6 '14 at 14:37
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    “How many Fourth of Julies have lacked fireworks?” – tchrist Jul 6 '14 at 14:39
  • @VivdD - that's a really good question! I would also use "Tuesday the 25ths", because I feel like all "[day of week] the [Xth]" effectively function like single-word names for the days. I pointed out that "Friday the 13th" is a common set phrase because I think that makes the argument for putting -s at the end even stronger in this case than in the general case. – alcas Jul 6 '14 at 15:19

Actually, "Friday 13th" itself seems odd to me. I would write "Friday the 13th".

Regardless, I would write "Fridays the 13th" for the plural, by analogy with nouns taking a postfix adjective like "postmasters general" or "mothers-in-law".

  • How would you explain that this 'serious' web page scienceworld.wolfram.com/astronomy/FridaytheThirteenth.html uses 'Friday the 13ths'? – VividD Jul 6 '14 at 7:17
  • Not everyone care about usage as much as we do? – szarka Jul 6 '14 at 7:20
  • @VividD It would have been helpful to have included your research / reference in your question. – andy256 Jul 6 '14 at 7:38
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    That, e.g., "attorneys general" rather than "attorney generals" is correct should be easy to confirm. See, e.g., Garner's Modern American Usage under PLURALS. I don't have an authoritative reference for dates like those in VividD's example, specifically, but the principle seems to me to be the same: "the 13th" modifies "Friday" just as, e.g., "general" modifies "attorney". – szarka Jul 6 '14 at 7:46
  • Here are two example of my suggested usage in reputable publications: time.com/money/2867978/safe-to-invest-on-friday-the-13th and parade.condenast.com/169367/marilynvossavant/… . – szarka Jul 6 '14 at 7:54

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