Wanna be editors! Here's a li'l fun for you―"or" not.
Despite what we've been taught about subject-verb agreement―the verb always agrees with the subject―it's often not so simple, especially if "or" is involved.
"Or" can connect two subjects in a sentence: in this case "plums" and "apple." We might think, "Oh, that's simple. More than one subject means 'plural,' so the verb must be plural, too."
But, in this case, "or" is involved. If "or" connects two singular subjects, the verb is almost always singular.*
For example, "An apple or a plum ____ all I need for a snack."
"Is" is singular. "Are" is plural. Based on the advice above, we would use "is."
Our example is a bit more complex than the above example because one of the subjects is plural (plums) and one is singular (apple). The one that is singular is closest to the verb. And, yes, proximity is a guiding principle in grammar.
THE PROXIMITY PRINCIPLE
Four plums or an apple is nearly the same amount of food.
An apple or four plums are nearly the same amount of food.
*Einsohn, A. (2011). The copyeditor's handbook (3rd ed.). Berkeley, CA: University of California Press.
Meet the Editor
I'm Coreen, and I am a copy editor, writer, instructor, digital marketer, and student of PR and Communications for organizations doing positive work in the world.