Question

When is it appropriate to break the rule that requires subjects joined by and to use a plural verb

Answer 1

It is appropriate to break the rule that requires subjects joined by and to use a plural verb when: the two subjects separated by and refer to the same person or thing. Examples are: Peanut butter and jelly is my favorite sandwich. Red beans and rice is my mom's favorite dish.

Answer 2

it is appropriate to break the rule that requires subjects joined by and to use a plural verb when either  and neither are subjects. They always take singular verb.

For example :

Either of us is capable of doing the job