The idiom 'Cross your Ts and dot your Is' is often written with apostrophes as though they were in the possessive forms:

Cross your T's and dot your I's

It's ubiquitous online, even on dictionary websites. But I don't understand why the apostrophes and don't know the rule of grammar that permits it. Can someone please explain the correct rule that governs writing it to me?


1 Answer 1


It's an evolving orthographic style.

The orthographic "rule" current when I was growing up in the 1950s was that the plurals of "non-words" (numbers, letters, initialisms) should be formed with -'s.

  • For instance, what I have just written as the 1950s was supposed to be written as the 1950's.

That rule was still current when I was in graduate school in the 1970s; but a few writers and publishers were already pluralizing these forms with bare -s, and over the last forty or fifty years most publishers and styleguides have adopted that style. But there are still many who follow the old "rule".

  • 1
    A way of representing this visually so that the pluralizing s isn't thought of as "part" of the word is to put it in a lower font size than the word it modifies. This produces a similar effect to DOs and DON'Ts without having to resort to the use of capitals. May 12, 2018 at 4:47

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