On the surface, subject-verb agreement is a simple topic: almost every sentence requires a subject and a verb, and that verb (and everything else in the sentence) should be properly conjugated to match the subject. In other words, if your subject is singular, your verb should be singular; if your subject is plural, your verb should be plural; if your subject is first-person, then your verb should be first person; and so on.
INCORRECT: My brother are ski instructor.
CORRECT: My brother is a ski instructor.
INCORRECT: My sisters is detective.
CORRECT: My sisters are detectives.
INCORRECT: I are a writer.
CORRECT: I am a writer.
Ninety-five percent of the time, subject-verb agreement is just that easy—you have a subject, you properly conjugate its verb without even thinking, and you move on. Every now and then, however, complications creep in. Usually, these difficulties arise because of a long or confusing sentence structure has made the subject of the sentence unclear.
As I watch, a strange blue substance full of floating, glowing spheres spread across the window.
I’ve italicized the verb in that subject, but where is the subject? It’s not spheres—the glowing spheres are inside the subject, which is the substance. Substance is singular, not plural—so it doesn’t spread, it spreads.
As I watch, a strange blue substance full of floating, glowing spheres spreads across the window.
Another frequent cause of subject-verb disagreement is compound subjects—when more than one subject is performing a single action in unison. Compound subjects are treated as a plural subject, even if the individual subjects are singular:
INCORRECT: My father and mother tells me to behave myself.
CORRECT: My father and mother tell me to behave myself.
Note: A compound subject will always be two or more subjects joined by the word and. If the subjects are joined by a phrase such as together with, as well as, or along with, then the first subject determines the conjugation of the verb:
My wife, together with her sisters, is going on vacation.
My wife and her sisters are going on vacation.
The conjunction or also doesn’t create compound subjects; if two potential subjects are paired using the word or (or nor), the verb should agree with whichever subject is closest to it:
Either my cousin or my friends are going to pick me up after work.
Neither my friends nor my cousin is going to be able to pick me up.
So remember to keep an eye on any particularly long and complicated sentences and any sentences with compound subjects to be sure that the subject-verb agreement is intact. Next week, we’ll cover other situations in which problems with subject verb agreement commonly arise.