apostrophe

 The principal functions of the apostrophe are to indicate omitted letters (don’t, can’t, wouldn’t) and to show the possessive (strictly, the genitive) case (John’s book, the bank’s money, the people’s choice).

 Two types of error occur with some frequency and are worth noting. They involve the following:

 1. Multiple possessives. This problem can be seen here: "This is a sequel to Jeremy Paul’s and Alan Gibson’s play" (Times). The question is whether both of the apostrophes are necessary, and the answer in this instance is no. Because the reference is to a single play written jointly, only the second-named man needs to be in the possessive. Thus, it should be "Jeremy Paul and Alan Gibson’s play." If the reference were to two or more plays written separately, both names would have to carry apostrophes. The rule is that when possession is held in common, only the nearer antecedent should be possessive; when possession is separate, each antecedent must be in the possessive.

 2. Plural units of measure. Many writers who would never think of omitting the apostrophes in "a fair day’s pay for a fair day’s work" often do exactly that when the unit of measure is in-