Like all other Oto-Manguean languages, Otomi is a tonal language, and most varieties distinguish three tones. Nouns are marked only for possessor; the plural number is marked with a definite article and a verbal suffix, and some dialects keep dual number marking. There is no case marking. Verb morphology is either fusional or agglutinating depending on the analysis. In verb inflection, infixation, consonant mutation, and apocope are prominent processes. The number of irregular verbs is large. A class of morphemes cross-references the grammatical subject in a sentence. These morphemes can be analysed as either proclitics or prefixes and marks for tense, aspect and mood. Verbs are inflected for either direct object or dative object (but not for both simultaneously) by suffixes. Grammar also distinguishes between inclusive 'we' and exclusive 'we'.