The simple definition of subject-verb agreement is that when the noun is plural, the verb must also be plural. Conversely, when one is singular, the other one must be singular. There are some variations on this rule when dealing with compound subjects.
Another common problem is when the writer confuses the subject of the sentence with a phrase that comes between the subject and the verb. For example: One of my goals is to be on time to work. The word "goals" is plural, but the subject of the sentence is "one," which is singular; therefore, the verb must agree with the singular subject.
Other examples of subject-verb agreement arise when the writer is not completely sure which form of a verb should be used if the word appears to be plural.
Janie Sullivan, MBA, MAEd, has been teaching adult learners for over 20 years. She has taught online over 15 years, specializing in writing, communications, and small business applications. Janie directs the Center for Writing Excellence where she offers writing, editing, and formatting services for writers. She has been published in several newspapers and magazines as well as multiple online sites. She teaches communication, business strategy, leadership, and management courses. Janie has published a book "Develop and Deliver an Online Class." This is the third book she has written about writing and teaching online. She also has published a novel and an anthology of short stories.