Q. Since the late 1980s, when I got my first copy of CMOS, I have understood that verbs associated with a noun used to group plural items should correspond with the singular, grouping noun. For example, “A growing number of reports has revealed . . .” Microsoft Word, however, keeps indicating a grammatical error when I follow this rule and was placated when I changed “has” to “have” in the above example. Can you please clarify who is right? Is it I or the copyeditors consulted by Bill Gates?
A. Microsoft’s grammar-checking software happens to be right in this case. Number as a collective noun takes a singular or plural verb depending on the article (definite the or indefinite a) that precedes it:
The number of pizzas ordered this year has doubled.
but
A number of studies have shown that stuffing a pizza with spinach triples the edibility of that sinewy vegetable.
Most collective nouns do tend to be invariably singular in American English. Those that, like number, vary according to circumstance include words like percentage and any fraction—one-third (or a third), one-half (or half), two-thirds, etc. Like number, these take a singular verb when preceded by the (common for percentage but rare for fractions). Otherwise, the verb agrees with the number of the noun in any prepositional phrase that follows:
After today’s enormously stressful workshop, a third of the attendees have decided to skip the entrée, preferring instead to dine on the wine.
but
Unfortunately, seven-eighths of last year’s vintage was spoiled.