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
Another letter composed of two elements to represent two regional pronunciations, now obsolete, was ㅱ, which transcribed the Chinese initial 微. This represented either "m" or "w" in various Chinese dialects, and was composed of ㅁ plus ㅇ. In ’Phags-pa, a loop under a letter, ꡧ, represented after vowels, and Ledyard proposes this rather than the null symbol was the source of the loop at the bottom, so that the two components of ㅱ reflected its two pronunciations just as the two components of ㆁ "ng" did. The reason for suspecting that this derives from ’Phags-pa ꡧ "w" is that the entire labio-dental series of both ’Phags-pa and the Korean alphabet6, used to transcribe the Chinese initials 微非敷 "w, v, f," have such composite forms, though in the case of ’Phags-pa these are all based on the letter ꡜ "h" (ꡤ "etc."), while in Hangul, which does not have an "h" among its basic consonants, they are based on the labial series ㅁ "m," ㅂ "b," ㅍ "p."