When two or more subjects are joined with the word “and,” use a plural verb. But when one subject is the main focus and a second subject is just tagging along, use a singular verb. You’ll know when a subject is tagging along, because it will be set off in commas. For instance:
- Plural subject: Red, white and blue are the official colors of the Fourth of July.
- Singular subject: Red, along with white and blue, is the official color of the Fourth of July.
- Plural subject: Janie and Jackie are going to run a half-marathon today.
- Singular subject: Janie, alongside her friend Jackie, is going to run a half-marathon today.