English Grammar for the Utterly Confused - Laurie Rozakis 2003
Special Problems in Agreement
Chapter 5 Agreement: Matching Sentence Parts
Part 2 Usage and Abusage
The rules for agreement are straightforward, but some thorny problems do arise. Here are the two most challenging issues: hard-to-find subjects and intervening phrases.
1. Identify hard-to-find subjects.
Some subjects can be harder to find than others. Subjects that come before the verb are especially tricky. However, a subject must still agree in number with its verb, as the following examples show:
The plural subject tires requires the plural verb were.
2. Ignore intervening phrases.
Disregard words or phrases that come between the subject and the verb. A phrase or clause that comes between a subject and its verb does not affect subject-verb agreement.
The singular subject captain agrees with the singular verb stands. Ignore the intervening prepositional phrase “of the guards.”