In any sentence, it is important that the subject and verb agree.
A singular subject must take a singular verb so that they agree. If a subject is in the third person, the present singular verb is most always followed by –s or –es. Plural subjects must take plural verbs in order to agree. See the examples below (subjects will be in italics and verbs will be in bold).
The cat plays with the yarn. (s)
The cats play with the yarn. (p)
Tammy watches the debate on the news. (s)
They watch the debate on the news. (p)
The document needs to be shredded. (s)
The documents need to be shredded. (p)
Compound subjects must also agree with their verbs. Compound subjects are made up of two or more subjects, and they are connected by and or or. When the subjects are joined by and, the verb is plural. The only exception is when compound subjects refer to a singular idea. When joined by or, the verb must agree with the subject closest to it. For example:
Jen and Chris live in Memphis.
Genetics and behavior work together to determine one’s risk for cancer.
The professor or his assistants grade the papers.
The police officers or the chief files reports.
The yoga instructor and health coach is Laura. (compound subject, but singular idea)
Usually when referring to groups, the verb is singular. For example:
The brothers get along very well. (brothers is a plural subject)
The family gets along very well. (family refers to a group)
The geese fly south for the winter.
The flock flies south for the winter.
Indefinite pronouns, such as “anyone,” “everyone,” “neither,” “nobody,” etc., take singular verbs.
Everyone watches the runner cross the finish line.
Nobody likes to feel excluded.