Hanja
Although a phonetic Korean alphabet, now known as Chosŏn'gŭl or Hangul, had been created by Sejong the Great, it did not come into widespread official use until the late 19th and early 20th century. Thus, until that time it was necessary to be fluent in reading and writing Hanja in order to be literate in Korean, as the vast majority of Korean literature and most other Korean documents were written in Literary Chinese, using Hanja as its primary script. Today, a good working knowledge of Chinese characters is still important for anyone who wishes to study older texts (up to about the 1990s), or anyone who wishes to read scholarly texts in the humanities. Learning a certain number of Hanja is very helpful for understanding the etymology of Sino-Korean words, and for enlarging one's Korean vocabulary. Today, Hanja are not used to write native Korean words, which are always rendered in Hangul, and even words of Chinese origin—"Hanja-eo" ()—are written with the Hangul alphabet most of the time, with the corresponding Chinese character often written next to it in order to prevent confusion with other characters or words with the same phonetics.
Korean phonology
In native Korean words, does not occur word initially, unlike in Chinese loans (Sino-Korean vocabulary). In South Korea, it is silent in initial position before and , pronounced before other vowels, and pronounced only in compound words after a vowel. The prohibition on word-initial is called the "initial law" or (). Initial is officially pronounced in North Korea. In both countries, initial in words of foreign origin other than Chinese is pronounced .This rule also extends to in many native and all Sino-Korean words, which is also lost before initial and in South Korean; again, North Korean preserves the phoneme there. Korean has eight vowel phonemes and a length distinction for each. Long vowels are pronounced somewhat more peripherally than short ones. Two more vowels, the mid front rounded vowel ( ) and the close front rounded vowel ( ), can still be heard in the speech of some older speakers, but they have been largely replaced by the diphthongs and , respectively. In a 2003 survey of 350 speakers from Seoul, nearly 90% pronounced the vowel as .