"Verbs are formally inflected principally for mood and tense by a grammatical particle suffixed to the stem. Most verbs also mark affective and effective "voice" (not equivalent to the notions "transitivity" or "causation") where the former indicates that the subject undergoes the action named by the stem, and the latter signals that the subject directs the action of the stem. Mood is also marked implicitly by grammatical formatives which also mark tense categories. These signal that the verbal event is, for example, unreal, possible, potential, or a real, and actual. There are three simple tenses (past, present, and future), and a series of perfects."