Origin of Hangul
Ledyard holds that the Koreans adopted five core consonant letters from ’Phags-pa, namely ㄱ "g" , ㄷ "d" , ㅂ "b" , ㅈ "j" , and ㄹ "l" . These were the consonants basic to Chinese phonology, rather than the graphically simplest letters (ㄱ "g" , ㄴ "n" , ㅁ "m" , and ㅅ "s" ) taken as the starting point by the "Haerye." A sixth letter, the null initial ㅇ, was invented by Sejong. The rest of the consonants were developed through featural derivation from these six, essentially as described in the "Haerye"; a resemblance to speech organs was an additional motivating factor in selecting the shapes of both the basic letters and their derivatives.
Origin of Hangul
Although several of the basic concepts of the Korean alphabet were inherited from Indic phonology through the ’Phags-pa script, such as the relationships among the homorganic consonants and, of course, the alphabetic principle itself, Chinese phonology played a major role. Besides the grouping of letters into syllables, in functional imitation of Chinese characters, according to Ledyard it was Chinese phonology, not Indic, that determined which five consonants were basic, and were therefore to be retained from ’Phags-pa. These included the plain stop letters, ꡂ "g" for ㄱ "g" , ꡊ "d" for ㄷ "d" , and ꡎ "b" for ㅂ "b" , which were basic to Chinese theory, but which represented voiced consonants in the Indic languages and were not basic in the Indic tradition. The other two letters were the plain sibilant ꡛ "s" for ㅈ "j" (ㅈ was pronounced in the fifteenth century, as it still is in North Korea) and the liquid ꡙ "l" for ㄹ "l" .