Is this good guidance? Mass nouns are sometimes followed by a prepositional phrase, such as number of plus a plural noun. The article that precedes the mass noun signals whether the mass noun or the number of the noun in the prepositional phrase controls the number of the verb. If the definite article the precedes, the mass noun controls, and typically a singular verb is used {the quantity of pizzas ordered this year has increased}. If an indefinite article (a or an) precedes, then the number of the noun in the prepositional phrase controls {a small percentage of the test takers have failed the exam}. Is there ever an exception to this rule (i.e., if an indefinite article [a or an] is used, can the verb ever be singular? And if a definite article [the] precedes, can a plural verb be used)? Or is this a hard and fast ironclad rule? BTW, should a comma separate 'hard and fast, ironclad rule? Thanks.
I can't think of an exception to #1 off the top of my head. I'd say yes to #2, though I think I would write it hard-and-fast, and the 'ironclad' seems redundant.
I'd say that you should not rely on grammar books in some cases and just go with your gut. To help you go with your gut, when in a dilemma, use the same sentence for both examples. -The quantity of pizzas ordered this year has increased. -A quantity of pizzas ordered this year have increased. (I would still use has here, because it is the quantity that has increased, not the pizzas themselves.) -a small percentage of the test takers have failed the exam. (It is the test takers who have failed the exam, not a small percentage.) -the small percentage of the test takers has failed the exam. (This sentence is not grammatically correct since definite article the cannot be used here. It could be used if it was followed by a relative clause: The small percentage of the test takers who have failed the exam. But it still needs to be treated as plural.
