In the example about John and Lisa, what grammatical issue exists?

In the context of grammar, the subject "Neither John nor Lisa" is treated as singular when determining the correct verb agreement. Therefore, the correct form of the verb to use would be "is" instead of "are." According to the rules of subject-verb agreement, when a compound subject is introduced by "neither/nor," the verb must agree with the closest subject. Since "Lisa" is singular and follows "neither/nor," the correct verb form should be singular as well.

This grammatical rule helps maintain clarity and correctness in sentence structure, ensuring that the subject and verb agree in number. Consequently, using "is" in this instance would be the appropriate choice to reflect singular agreement, aligning with standard English grammar practices.