As you recall, verbs have five characteristics: person, number, tense, mood, and voice. The first two characteristics (person and number) are revealed solely by personal endings. Take apart the word “infinitive,” and you will find the prefix “in-” meaning “not” and the base “fin” from f ī nI s (“end”). An infinitive, then, is a verb form that doesn't have personal endings, but it does have tense and voice.