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Q. We are publishing plays, and the dialogue is sometimes written to convey sound as well as sense. The playwright has “August 25th, 1989.” Is there any guideline preventing us from including the comma after the ordinal?
A. No, since this order of elements requires the year to be set off with commas. Regardless, the best way to write dialogue is the way you want it to be spoken rather than according to style guidelines for print. (We generally don’t expect people to speak in Chicago style.) If you want a slight pause (which most speakers would naturally supply before the year), write “August twenty-fifth, 1989.” Although that breaks Chicago’s style of using cardinal numerals, not spelled-out ordinals, in dates (August 25, 1989), spelling out “twenty-fifth” tells the actor how to read the number.