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
The five adopted letters were graphically simplified, retaining the outline of the ’Phags-pa letters but with a reduced number of strokes that recalled the shapes of the speech organs involved, as explained in the "Haerye." For example, the box inside ’Phags-pa ꡂ "g" is not found in the Korean ㄱ "g" ; only the outer stroke remains. In addition to being iconic for the shape of the "root" of the tongue, this more easily allowed for consonant clusters and left room for an added stroke to derive the aspirated consonant ㅋ "k" . But in contrast to the "Haerye" account, the non-stops "ng" , ㄴ "n" , ㅁ "m" , and ㅅ "s" were derived by "removing" the top stroke or strokes of the basic letters. (No letter was derived from ㄹ "l" .) This clears up a few points that had been problematic in the "Haerye." For example, while it is straightforward to derive ㅁ "m" from ㅂ "b" by removing the top of ㅂ "b" in Ledyard's account, it is not clear how one would derive ㅂ "b" by adding something to ㅁ "m", since ㅂ "b" is not analogous to the other stops: If ㅂ "b" were derived as in the "Haerye" account, it would be expected to have a horizontal top stroke similar to those of ㄱ "g" , ㄷ "d" , and ㅈ "j" .