Plurals of letters

[Gnisy]

How should the plural of letters look like? For instance, should A (as in the grade) in plural form be As or A's. Similarly, should CD as in compact disc, be CDs or CD's. While we're on the subject, how do you actually write
dos and don'ts / do's and don'ts?

Many thanks for any replies.
* I've read the thread on CDs but I'd still like to know if the same applies for the A's and the do's.

[Clanad]

The Chicago Manual for Style in Writing states that the apostrophe is to be used. As an example A's, B's, etc. This would be true with lower case letters as well. CD in my opinion would also require the apostrophe useage, since it's not a real word. therefore, in my opinion, it should be rendered CD's...

[kempie]

This may be another British vs. US topic since in Standard English the apostrophe is never used to denote simple plurals.

Thus CDs and As are perfectly acceptable. However it must be noted that in the case of certain letters (Aa, Ii and Uu) this could lead to confusion, e.g. us would appear as us, and so in this "special case" an apostrophe may well alleviate any ambiguity i.e. u's.

http://www.apostrophe.fsnet.co.uk/

[jno]

Yes, I think the usage of many full stops and apostrophes in abbreviations is more American than British, so it depends where you are Gnisy. Kempie, I just capitalise individual letters to make it clear - As, Bs, Cs; I suppose it's just possible that, on some occasions, it might be vital to show that they're lower case but it's never actually happened to me.

[Quizmonster]

Fowler's Modern English Usage - usually seen as the 'bible' in matters of British English use says:

"Though once commonly used in the plural of abbreviations and numerals (QC's, the 1960's) the apostrophe is now best omitted in such circumstances: MAs, MPs, the three Rs. Except that it is normally used in contexts where its omission might possibly lead to confusion, eg dot your i's and cross your t's; there are three i's in inimical."

So, CDs it is

[rojash]

Clanad, your answer was very enlightening for me. I regularly read the New York Times, and it used to drive me mad to see all those (as I believed) spurious apostophes. It never occurred to me that punctuation rules might differ between the US and the UK.

[Gnisy]

Thanks to all for your answers.