Language, the principal means used by human beings to communicate with one another. Language is primarily spoken, although it can be transferred to other media, such as writing. If the spoken means of communication is unavailable, as may be the case among the deaf, visual means such as sign language can be used. A prominent characteristic of language is that the relation between a linguistic sign and its meaning is arbitrary: There is no reason other than convention among speakers of English that a dog should be called dog, and indeed other languages have different names (for example, Spanish perro, Russian sobaka, Japanese inu). Language can be used to discuss a wide range of topics, a characteristic that distinguishes it from animal communication. The dances of honey bees, for example, can be used only to communicate the location of food sources (see Honey Bee: Communication). While the language-learning abilities of apes have surprised many—and there continues to be controversy over the precise limits of these abilities—scientists and scholars generally agree that apes do not progress beyond the linguistic abilities of a two-year-old child (see Communication: Communication Among Animals).