In addition to the terms used for the parts of speech, traditional grammatical analysis has also given us a number of other categories, including “number,” “person,” “tense,” “voice” and “gender.” These categories can be discussed in isolation, but their role in describing language structure becomes clearer when we consider them in terms of agreement. For example, we say that the verb loves “agrees with” the noun Cathy in the sentence Cathy loves her dog.
This agreement is partially based on the category of number, that is, whether the noun is singular or plural. It is also based on the category of person, which covers the distinctions of first person (involving the speaker), second person (involving the hearer) and third person (involving any others). The different forms of English pronouns can be described in terms of person and number. We use I for first person singular, you for second person singular, and he, she, it (or Cathy) for third person singular. So, in the sentence Cathy loves her dog, we have a noun Cathy, which is third person singular, and we use the verb loves (not love) to “agree with” the noun.