I have a sentence that requires a form of "to be" referring to something in singular and plural at the same time:

The major source for pharmaceutical residues in rivers [is/are] wastewater treatment plants.

The verb "to be" refers to the source (singular) and the waste water treatment plants (plural) as they are the same thing. Which is the right way to say it? This is a global statement, so waste water treatment plants need to be plural (it is not just on plant). They are considered one source (or one type of sources), so "the major source" should be singular.

Another exemple:

The main natural hazard in this region [is/are] avalanches.

This is probably linked to Singular Noun With Plural Verb? and When expressing a class of things, should I use a singular or a plural form?, but they don't have accepted answers.

  • 4
    "source" is the subject here, and this is in the singular, so the verb must agree with the number of the subject. So the verb must be "is". In your second example, "hazard" is also singular, and the same rule applies. The verb must be "is".
    – Billy Kerr
    Jun 21, 2023 at 10:51

1 Answer 1


The word "source" is the root of the subject, so "is" is correct.

The verb always agrees with the subject, not the complement.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .