A verb is a word that describes an action, occurrence, or state of being in a sentence. It is one of the main parts of a sentence or phrase, along with nouns. Verbs can be expressed in different tenses, depending on when the action is being performed. For example, "walked" is a past-tense verb, "were" is a past-tense verb that shows a state of being, "will call" is a future-tense verb phrase, and "itch" is a present-tense verb. Verbs can be classified in different ways, such as by what kind of action they signify. There are many types of verbs, including physical verbs, mental verbs, state of being verbs, and auxiliary verbs. Verbs can also be compound verbs, which are two words that combine to make one meaning. Linking verbs, also known as copular verbs, are not followed by objects but are followed by phrases that give extra information about the subject.