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
If Ledyard is correct, the graphic base of Hangul forms part of the great family of alphabets that spread from the Phoenician alphabet, through Aramaic, Brāhmī, and Tibetan. However, this is only one component of its derivation; Hangul did not derive from ’Phags-pa in the gradual and unconscious way that Tibetan derived from Brāhmī. Ledyard wrote in his doctoral thesis: