 Final voiceless stops and therefore the checked "tones" have disappeared from most Mandarin dialects, spoken in northern and southwestern China, but have been preserved in the southeastern branches of Chinese, such as Yue, Min, and Hakka.Tones are an indispensable part of Chinese literature, as characters in poetry and prose were chosen according to tones and rhymes for their euphony.This use of language helps the reconstruction of the pronunciation of Old Chinese and Middle Chinese since the Chinese writing system is logographic, rather than phonetic.