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.
Hangul
With vowel letters, a short stroke connected to the main line of the letter indicates that this is one of the vowels that "can" be iotized; this stroke is then doubled when the vowel "is" iotized. The position of the stroke indicates which harmonic class the vowel belongs to, "light" (top or right) or "dark" (bottom or left). In the modern alphabet, an additional vertical stroke indicates i-mutation, deriving , , and from , , and . However, this is not part of the intentional design of the script, but rather a natural development from what were originally diphthongs ending in the vowel . Indeed, in many Korean dialects, including the standard dialect of Seoul, some of these may still be diphthongs. Note: as a morpheme is ㅓ combined with ㅣ as a vertical stroke. As a phoneme, its sound is not by i-mutation of .