Editing English plurals (section)

===Plurals of letters and abbreviations===
The plural of individual letters is usually written with ''-'s'':<ref name="Fowler 2015">{{Cite book|page=633 |last1=Fowler |first1=H. W. |editor1-last=Butterfield |editor1-first=Jeremy |title= Fowler's Dictionary of Modern English Usage  |year=2015 |publisher=Oxford University Press |isbn=978-0-19-966135-0}}</ref> ''there are two a's in this sentence''; ''mind your p's and q's''; ''dot the i's and cross the t's''.

Some people extend this use of the [[apostrophe (mark)|apostrophe]] to other cases, such as plurals of numbers written in figures (e.g. "1990's"), words used as terms (e.g. "his writing uses a lot of ''but's''"). However, others prefer to avoid this method (which can lead to confusion with the [[possessive case|possessive]] ''-'s''), and write ''1990s'', ''buts''; this is the style recommended by ''[[The Chicago Manual of Style]]''.

Likewise, [[acronym]]s and initialisms are normally pluralized simply by adding (lowercase) ''-s'', as in ''MPs'', although the apostrophe is sometimes seen. Use of the apostrophe is more common in those cases where the letters are followed by periods (''B.A.'s''), or where the last letter is S (as in ''PS's'' and ''CAS's'', although ''PSs'' and ''CASs'' are also acceptable; the ending ''-es'' is also sometimes seen).

English (like Latin and certain other European languages) can form a plural of certain one-letter abbreviations by doubling the letter: p. ("page"), pp. ("pages"). Other examples include ll. ("lines"), ff. ("following lines/pages"), hh. ("hands", as a measure), PP. ("Popes"), SS. ("Saints"), ss. (or §§) ("sections"), vv. ("volumes"). Some multi-letter abbreviations can be treated the same way, by doubling the final letter: MS ("manuscript"), MSS ("manuscripts"); op. ("opus"), opp. ("opera" as plural of opus).

However, often the abbreviation used for the singular is used also as the abbreviation for the plural; this is normal for most units of measurement and currency. The [[SI]] unit symbols are officially not considered abbreviations and not pluralized, as in 10&nbsp;m ("10 metres").