Using "are/is" after a list with "and/or" [duplicate]

Possible Duplicate:
Singular or plural following a list

James and Mark are going to help you.

Here, I use 'are' because the subject is plural.

James or Mark are going to help you.

James or Mark is going to help you.

Here, I’m not sure whether to use 'are' or 'is' because the subject isn't plural(?) It’s one or the other – so does that mean the subject is still plural, and I should use 'are', or is 'is' correct here?

Solution 1:

Each of your sentences is a compound sentence; that is, each is composed of two sentences reduced to one:

James is going to help you and Mark is going to help you => James and Mark are going to help you.

The conjunction and makes the subject a plural subject: James and Mark, two guys, are going to help you.

(Either [Implied but optional]) James is going to help you or Mark is going to help you => James or Mark are going to help you.

The conjunction or makes the subject a singular subject: James or Mark, only one of the two guys, is going to help you. I don't know which, but both won't.

You can always avoid the problem by changing the verb from is going to to will: