Cuneiform was the first known form of written language, but spoken language is believed to predate writing by tens of thousands of years at least. A language is a system of visual, auditory, or tactile symbols of communication and the rules used to manipulate them. Language can also refer to the use of such systems as a general phenomenon. Language is considered to be an exclusively human mode of communication; although other animals make use of quite sophisticated communicative systems, none of these are known to make use of all of the properties that linguists use to define language.