A verb expresses an action or state of being. There are transitive verbs that require a direct object and intransitive verbs that do not. Verbs can also describe a state of being by linking the subject to a noun or adjective. Helping verbs are used to form tenses like past or perfect. Tenses like present, past and future indicate when an action occurs. The subject can perform or receive the action of the verb. Mood shows the tone or attitude of a statement. Some verbs can function as other parts of speech by adding suffixes like "-ing" or "-ed".