Verbs are the most important words in a sentence, as a single verb can form a complete one-word sentence. Verbs describe either the action that a subject performs, such as "run" or "fight", or the state of being of a subject, such as "be" or "seem". Verbs always have a subject that they are describing the action or state of. Additionally, verbs are unique in English in that they change form depending on tense, aspect, and subject number, with some verbs having up to five different forms like "to work, work, works, worked, working".