Omission and confusion
Adding 's to singular nouns had by then become the accepted way of indicating the genitive case (the king's crown).
In Old English the genitive was indicated by an - es ending (the kinges crown), so the possessive apostrophe may have originally marked the missing e. For this reason, 18th-century grammarians were at odds over the use of a final apostrophe to mark plural genitives (the kings' crowns) as some argued there were "no missing letters".
Conflicting Lndon street signs point to similar debate over the use of the apostrophe when a singular noun ends in - s (St James' Court, St James's Square, St James Close).
Unfortunately, the apostrophe was used by some earlier writers to separate off a plural - s in words ending in a vowel (two potato's). Once broad agreement was reached to reserve it for omission and possession, there were frantic attempts to stamp this out. But confusion had set in and what Fowler calls this "fatuous vulgarism" has been with us ever since. Even educational writers fall prey to it sometimes: how else can one comfortably write: "The do's and don'ts of apostrophe usage?" SUE PALMER
Visit Sue Palmer's 'Home for Abused Apostrophes' at:www.nuff.ox.ac.ukusersmartinlanguagelive.htm