I’m asking this out of nothing but sheer curiosity. How would you indicate plural S in a sentence? For example: ‘Do not use two Cs in Necessary, but do use two Ss.’ Logic dictates what I have above is correct. If the plural of C is Cs then the same applies to S, yes? But I think it’s the pronunciation that makes me stop and think. Plural C is ‘seas’ whereas plural S is ‘esses’ and I always feel like Ss fails to represent the pronunciation.
I know in the USA (where I'm originally from) it's okay to use an apostrophe. C's and S's. I got a LOT of flack when I moved here, and was treated as if I was ignorant about apostrophes. At first I felt quite ashamed, then went WAIT A MINUTE! And I looked it up in my Webster's dictionary, and lo ...using apostrophes for this kind of thing, or even for dates, such as 'the 1950's' was correct—at least in the USA. I've now dropped the apostrophe from dates, so I now write 'the 1950s' because it's patently obvious what is meant. However, when it comes to a plural of a letter ...I'll stick with the apostrophe. C's and S's it is. There is also some controversy about the possessive form of proper names, when they end in 's.' Like Jones. Do you write 'the Jones' house?' Or do you write 'the Jones's house.' Or James' dog, versus James's dog. I choose the latter, because it's closer to the pronunciation—and makes total sense. And is also grammatically correct, depending on what source you respect. I think the general rule of thumb about non-possessive apostrophes is that they represent something that's left out. Don't, as opposed to do not. Can't as opposed to can not. So, taking that logic a step further, I suppose S's is leaving out the spoken' e sound. Instead of Ses, we write S's? Instead of Joneses, we write Jones's? But that's getting picky. There is a lot of difference between deliberately choosing to use an apostrophe for this kind of thing, and just sprinkling them around as if they were seasoning. Or adding them to a word that is already possessive. Hers, yours, theirs. Or a noun that is already in its plural form : carrots, potatoes, cocktails.
Pronounce them out loud. You say "Esses" and "Sees". There's already an S sound on the end of the word Ess, but not on the word See, it ends with a long E sound ("ee"). See?
Oh, I see the reasoning now, but you’re still using a possessive S where it’s grammatically incorrect. Not sure if there’s a hard and fast rule for this, but I suppose S’s is a good a way as any to force a person to say esses.
I think consistency is important. If you are talking about S's and C's or P's and Q's in the same sentence or paragraph, it's going to look pretty weird if one of them has an apostrophe and the other ones don't. I'd use the apostrophe for both. Or not. Ss and Cs or Ps and Qs. The apostrophe is correct in terms of American English. The example I gave of the -es ending was out of my own head. Ignore it.
It depends on your style guide. You can find either answer. There is a plural apostrophe, but it's rare. CM17 (6.116) The apostrophe has three main uses: to indicate the possessive case, to stand in for missing letters or numerals, and—in rare instances—to form the plural of certain expressions. (I actually had the section number memorized, so it was easy to find . . . I've looked this up before, heh.) The current CM17 says to use plural apostrophes with lowercase letters (p's and q's) but not capitals (Ps and Qs). You typically italicize lowercase "words used as words." Other guides use the plural apostrophe with both. Personally, this is one of rare times that I kind of ignore Chicago Manual. I like the apostrophes. They get used on words too. "As good as it gets." There are two as's in the above sentence.
