Tone is the use of pitch in language to distinguish lexical or grammatical meaning – that is, to distinguish or to inflect words. All verbal languages use pitch to express emotional and other paralinguistic information and to convey emphasis, contrast, and other such features in what is called intonation, but not all languages use tones to distinguish words or their inflections, analogously to consonants and vowels. Languages that do have this feature are called tonal languages; the distinctive tone patterns of such a language are sometimes called tonemes [ˈtəʊniːm], by analogy with phoneme. Tonal languages are extremely common in Africa, East Asia, and Central America, but rare elsewhere in Asia and in Europe; as many as seventy percent of world languages may be tonal. In many tonal African languages, such as most Bantu languages, tones are distinguished by their pitch level relative to each other, known as a register tone system. In multi-syllable words, a single tone may be carried by the entire word, rather than a different tone on each syllable. Often grammatical information, such as past versus present, “I” versus “you”, or positive versus negative, is conveyed solely by tone. In the most widely spoken tonal language, Mandarin Chinese, tones are distinguished by their distinctive shape, known as contour, with each tone having a different internal pattern of rising and falling pitch. Many words, especially those that are monosyllabic, are differentiated solely by tone. In a multisyllabic word each syllable often carries its own tone. Unlike in Bantu systems, tone plays little role in modern Chinese grammar, though the tones descend from features in Old Chinese that did have morphological significance (e.g. changing a verb to a noun or vice versa). Contour systems are typical of languages of the Mainland Southeast Asia linguistic area, including Tai–Kadai, Vietic and Sino-Tibetan languages. The Afroasiatic, Khoisan, Niger-Congo and Nilo-Saharan languages spoken in Africa are dominated by register systems. Some languages combine both systems, such as Cantonese, which produces three varieties of contour tone at three different pitch levels, and the Omotic (Afroasiatic) language Bench, which employs five level tones and one or two rising tones across levels. Many languages use tone in a more limited way. In Japanese, fewer than half of the words have a drop in pitch; words contrast according to which syllable this drop follows. Such minimal systems are sometimes called pitch accent, since they are reminiscent of stress accent languages, which typically allow one principal stressed syllable per word. However, there is debate over the definition of pitch accent, and whether a coherent definition is even possible.