from Phagspa, but rather seem to have been invented by Sejong or his ministers to represent the phonological principles of Korean. Two methods were used to organize and classify these vowels, vowel harmony and iotation. Of the seven vowels, four could be preceded by a y- sound ("iotized"). These four were written as a dot next to a line: ㅓㅏㅜㅗ. (Through the influence of Chinese calligraphy, the dots soon became connected to the line, as seen here.) Iotation was then indicated by doubling this dot: ㅕㅑㅠㅛ. The three vowels which could not be yotized were written with a single stroke: ㅡㆍㅣ. The Korean language of this period had vowel harmony to a greater extent than it does today. Vowels alternated according to their environment, and fell into "harmonic" groups. This affected the morphology of the language, and Korean phonology described it in terms of yin and yang: If a word had yang ('bright') vowels, then most suffixes also had to have a yang vowel; and conversely, if the root had yin ('dark') vowels, the suffixes needed to be yin as well. There was a third group called "mediating" ('neutral' in Western terminology) that could coexist with either yin or yang vowels. The Korean neutral vowel was ㅣ i. The yin vowels were ㅡㅜㅓ eu, u, eo; the dots are in the yin directions of 'down' and 'left'. The yang vowels were ㆍㅗㅏ, ə, o, a, with the dots in the yang directions of 'up' and 'right'. The Hunmin Jeong-eum states that the shapes of the non-dotted letters ㅡㆍㅣ were also chosen to represent the concepts of yin (flat earth), yang (sun in heaven), and mediation (upright man). (The letter ㆍ ə is now obsolete.) There was a third parameter in designing the vowel letters, namely, choosing ㅡ as the graphic base of ㅜ and ㅗ, and ㅣ as the base of ㅓ and ㅏ. A full understanding of what these horizontal and vertical groups had in common would require knowing the exact sound values these vowels had in the 15th century. Our uncertainty is primarily with the letters ㆍㅓㅏ. Some linguists reconstruct these as , respectively; others as . However, the horizontal letters ㅡㅜㅗ do appear to have all represented mid to high back vowels, . References Ledyard, Gari K. The Korean Language Reform of 1446. Seoul: Shingu munhwasa, 1998. Ledyard, Gari. "The International Linguistic Background of the Correct Sounds