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
Various fanciful speculations about the creation of Hangul were put to rest by the discovery in 1940 of the 1446 "Hunmin jeong-eum haerye" "Explanation of the "Hunmin Jeong-eum" with Examples". This document explains the design of the consonant letters according to articulatory phonetics and the vowel letters according to Confucian principles such as the "yin" and "yang" of vowel harmony (see below).