Grammatical tense is a way languages express the time at which an event described by a sentence occurs. In English, this is a property of a verb form, and expresses only time-related information. Tense, along with mood, voice and person, are three ways in which verb forms are frequently characterized, in languages where those categories apply. There are languages (mostly isolating languages, like Chinese) where tense is not expressed anywhere in the verb or any auxiliaries, but only as adverbs of time, when needed for comprehension; and there are also languages (such as Russian) where tense is not deemed very important and emphasis is instead placed on aspect. The exact number of tenses in a language is often a matter of some debate, since many languages include the state of certainty of the information, the frequency of the event, whether it is ongoing or finished, and even whether the information was directly experienced or gleaned from hearsay, as moods or tenses of a verb. Some grammarians consider these to be separate tenses, and some do not.
