O careless apostrophe: why do you permit your use as a marker of the plural? Are you so ambitious as to leap at each and every occasion when you might feature? As a marker of the possessive we find you highly desirable. As a marker of omission you begin to obtrude a little, though such contractions as “I’m”, “he’s”, “isn’t”, “don’t”, “can’t” etc. cannot be regarded as objectionable. Your identical twin, the single closing quotation mark, shares a key on the keyboard with you. Does this play any role in promoting some of your territorial expansionism?
The Passive Voice brings us a link to a discussion of the fate of the apostrophe. Their example, MA’s, seems just wrong, wrong, wrong to me, unless we are talking about an MA’s ability to get you a better job than a BA. Hart’s Rules (a title graced by our friendly little apostrophe) tells us, decisively as ever, “Omit the apostrophe in the plurals B. Litt.s, MAs, MPs, QCs, the sixties, the 1960s.” Of course they could have just left the examples out, though no doubt nobody at Oxford University Press would ever have dreamt that an apostrophe might nowadays elbow its way into a plural, non-possessive noun. There was a time when we (our forefathers) cared about the difference between King Street, Kings Street, and King’s Street. Maybe there was even a Kings’ Street. And they probably knew the King or Kings in memory of whom the street was named. Now it’s just a marker. I guess that is a loss, but not really a very big one.
The full discussion is at The English Project. There they reveal that we imported the apostrophe from France and that it was used first to indicate an omitted letter. It took a couple of hundred years for grammar books to be invented and to decree that the apostrophe should be used to form the possessive and not the plural. So in using it to form the plural those who insist on doing so can claim ancient precedent.
The Apostrophe Protection Society exists to preserve “the correct use of this currently much abused punctuation mark in all forms of text written in the English language”.