it (i.e. something specific)' to nitlacua 'I am eating'. Plural suffixes are never used to mark plural objects, only plural subjects. Unspecified objects are never plural. A Classical Nahuatl verb thus has the following structure: SUBJECT PREFIX + OBJECT PREFIX + VERB STEM + SUBJECT NUMBER (example: ti-quim-itta-h, we – them – see – plural, i.e., 'we see them') Direct arguments of the verb – that is, subject and object – are obligatorily marked on the verb. If there are both direct and indirect objects (which are not morphologically distinguished), only one may be marked on the verb. Other inflectional categories may be optionally marked, for example direction of motion. Other inflections include the applicative and causative, both valency changing operations; that is, they increase the number of arguments associated with a verb, transforming an intransitive verb into transitive, or a transitive verb into bitransitive. Tense and mood inflection The different tenses and moods are formed, somewhat as in Latin or Ancient Greek, by adding the person inflections to the appropriate verbal base or stem. Base 1 is the normal or citation form of the verb, also known as the imperfective stem, with no special suffixes. Base 2, also known as the perfective stem, is usually shorter in form than base 1, often dropping a final vowel, though formation thereof varies. Base 3, the hypothetical stem, is normally the same as base 1, except for verbs whose stem ending in two vowels, in which case the second vowel is dropped, and the stem vowel is often lengthened in front of a suffix. Imperfective tenses The present tense is formed from base 1. The plural subject suffix is -h. Examples: nicochi 'I am sleeping,' tlahtoah 'they are speaking,' nicchīhua 'I am making it.' The imperfect is similar in meaning to the imperfect in the Romance languages. It is formed with base 1, plus -ya or -yah in the plural. Sometimes the final vowel of the stem is lengthened. Examples: nicochiya 'I was sleeping,' tlahtoāyah 'they used to speak,' nicchīhuaya 'I was making it.' The habitual present, customary present, or quotidian tense is formed from base 1. The suffix is -ni, with the stem vowels sometimes lengthened before it. Rather than one specific event this tense expresses the subject's tendency or propensity to repeatedly or habitually perform the same action over time (e.g. miquini 'mortal,' lit. '(one who is) prone to die'.