There are 18 verb classes distinguished by the shape of their stem-forming prefixes. Classes 1, 2, 7, 10 and 15 cover intransitive verbs, and the rest of the classes involve transitive verbs. Transitive verbs have two prefix forms, one used for third person and first person singular and another used for the other persons (2nd person plural and singular and first person plural inclusive and exclusive). Clusivity distinctions as well as the distinction between second and first person is marked by the tonal pattern across the word (morphemes and stem do not have inherent lexical tone).