Subject-Verb Agreement in English Grammar
Subject-Verb Agreement means that a singular subject takes a singular verb and a plural subject takes a plural verb.
For example:
My brother is in town.
My brothers are in town.
In the first example the subject is singular: my brother. This makes the verb singular: is.
In the second example the subject is plural: my brothers. This makes the verb plural: are.
Subject
The first step is to identify whether the subject is singular or