In her list of the accepted uses of the apostrophe, the last listed are:
#7 "It indicates the plurals of letters" - eg - How many n's are there in Northallerton?
#8 "It also indicates the plurals of words"
The problem is that, while "#7" is a general usage, "#8" - as Ms Truss implies in depth elsewhere - is an extremely rare usage, and this difference really needs stressing at this point, for the sake of clarity.
Caxton: Dictionary of English Grammar (2000) claims that 'Apostrophes are sometimes used, with s, to make an informal plural form for words which are not usually found in the plural - hence "This project is interesting, but there are too many if's".'
I'd like to know which words (if any) other than:
but's, and's, if's, do's and don't's - have plurals constructed in this way. Also, what is accepted usage - Collins Softback ED (1990) has:
"do's and don't's" ;
"do - noun - informal British - a party - plural do's or dos"; and
"ifs and buts".
And is the point at which the 2000s become the 2000's (or vice versa) mid-way across the Atlantic part of another International Date Line?
And finally, (wrt p56 in Ms Truss's book) when did the "Ancient World" end? And do we write "Athens's first Olympic Games were a spectacle for the known world; Athens' next Olympics (if they take place) will be a spectacle for the whole world."?