Numerals Nahuatl has a vigesimal (base-20) numbering system. The base values are (1 × 20), (1 × 400), (1 × 8,000), (1 × 20 × 8,000 = 160,000), (1 × 400 × 8,000 = 3,200,000) and (1 × 20 × 400 × 8,000 = 64,000,000). Note that the prefix at the beginning means 'one' (as in 'one hundred' and 'one thousand') and is replaced with the corresponding number to get the names of other multiples of the power. For example, (2) × (20) = (40), (2) × (400) = (800). The in (and ) and the in are grammatical noun suffixes that are appended only at the end of the word; thus , and compound together as . Verbs The Nahuatl verb is quite complex and inflects for many grammatical categories. The verb is composed of a root, prefixes, and suffixes. The prefixes indicate the person of the subject, and person and number of the object and indirect object, whereas the suffixes indicate tense, aspect, mood and subject number. Most Nahuatl dialects distinguish three tenses: present, past, and future, and two aspects: perfective and imperfective. Some varieties add progressive or habitual aspects. Many dialects distinguish at least the indicative and imperative moods, and some also have optative and vetative/prohibitive moods. Most Nahuatl varieties have a number of ways to alter the valency of a verb. Classical Nahuatl had a passive voice (also sometimes defined as an impersonal voice), but this is not found in most modern varieties. However the applicative and causative voices are found in many modern dialects. Many Nahuatl varieties also allow forming verbal compounds with two or more verbal roots. The following verbal form has two verbal roots and is inflected for causative voice and both a direct and indirect object: Some Nahuatl varieties, notably Classical Nahuatl, can inflect the verb to show the direction of the verbal action going away from or towards the speaker. Some also have specific inflectional categories showing purpose and direction and such complex notions as "to go in order to" or "to come in order to", "go, do and return", "do while going", "do while coming", "do upon arrival", or "go around doing". Classical Nahuatl and many modern dialects have grammaticalised ways to express politeness towards addressees or even towards people or things that are being mentioned, by using special verb forms and special "honorific suffixes". Familiar verbal form: Honorific verbal