There are three principles governing subject-verb concord. They are grammatical, notional”
proximity. For example:
Everybody is happy with the decision.
The audience were brought to their feet at the sight of Superman in his wbeelchair.
Either you or I am responsible for the mistake.
In the first sentence IS is used to agree with singular subject Everybody, so grammatical principle is followed. In the second sentence WERE is used because the subject AUDIENCE is plural in meaning, so notional principle is followed. In the last sentence AM is used because the subject close to it is I, so the last principle is followed.
