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
Similarly, the coronal consonants (舌音 "tongue sounds") are said to show the (front of the) tongue bent up to touch the palate, the bilabial consonants (脣音 "lip sounds") represent the lips touching or parting, the sibilants (齒音 "incisor sounds") represent the teeth (in sibilants the airstream is directed against the teeth), and the guttural consonants (喉音 "throat sounds"), including the null initial used when a syllable begins with a vowel, represent an open mouth and throat. The labiodental consonants (輕脣音 "light lip sounds") are derived from the bilabial series. In all cases but the labials, the plain (清 "clear") stops have a vertical top stroke, the non-stops lack that stroke, and the aspirate stops have an additional stroke. There were a few additional irregular consonants, such as the coronal lateral/flap ㄹ , which the "Haerye" only explains as an altered outline of the tongue, and the velar nasal ㆁ . The irregularity of the labials has no explanation in the "Haerye," but may be a remnant of the graphic origin of the basic letter shapes in the imperial ’Phags-pa alphabet of Yuan Dynasty China.