Q: Please help me identify the rule that requires the singular verb in this construction: “The source of the funding is the contributions made by shareholders.” I’m trying to convince an ESL student of mine that he can’t say the source “are” the contributions. I’ve scoured all known sources and found nothing!
A: The rule here is that the verb agrees with the subject, not its complement (a word or phrase that follows a linking verb like “is” and describes the subject). So it’s correct to say “The source of the funding is the contributions made by shareholders.”
Turned around, the sentence could also read: “The contributions made by shareholders are the source of the funding.” In this case, “contributions” is the subject and “the source of the funding” is the complement.
If you want to cite another source for your student, look under “agreement” in The New Fowler’s Modern English Usage, 3rd ed., edited by R. W. Burchfield (p. 35):
“When a subject and a complement of different number are separated by the verb to be, the verb should agree with the number of the subject.”
Burchfield uses the example “the only traffic is oxcarts and bicycles.”
The same advice is given in the earlier, 2nd edition of Fowler, edited by Sir Ernest Gowers (p. 401): “The verb follows the number of the subject, whatever that of the complement may be.”
I hope this helps. And good luck with your student.