1750년, 신경준이 저술한 『훈민정음운해(訓民正音韻解)』에 따라 순음(脣音) ㅁ・ㅂ을 水, 후음(喉音) ㅇ・ㅎ을 土로 오행을 배속하는 법이 성명학에서 다수설(多數說)로 정착되었으나 1940년에 발견된, 훈민정음 원본인 『훈민정음해례(訓民正音解例)』는 순음 ㅁ・ㅂ을 土, 후음 ㅇ・ㅎ을 水로 배속하고 있다. 본 연구는 이로 인해 야기된 혼란을 해소하고자 국어학과의 융합연구를 통해 훈민정음의 자음오행 배속원리를 궁구한 후, 『훈민정음운해』의 오행 배속법이 갖는 음운학(音韻學)적인 역사와 배경을 살펴보았다. 그 결과, 우리말 음운과 중국 한자음운의 오행배속을 각각 달리 본 신숙주의 인식체계가 신경준으로 이어졌으며 『훈민정음운해』의 궁극적 저술 목표는 중국의 한자 음운체계와 소통(疏 通)하기 위한 ‘한자음운도(漢字音韻圖)’에 있었다는 점에 주목하였다. 따라서 우리말 음운을 우리글로 적으려고 한 한글 창제의 주된 취지, 음운(音韻)이 시대・환경에 따라 분별되는 성향, 순 한글과 한자의 발음이 동일한 현대의 음운적 특징에 의거하여 『훈민정음해례』의 오행 배속이 더 합당하다는 결론을 이끌었다. 또한 한글이 발음기관의 동작이나 모습을 상형(象形)한 문자이므로 한글 자형오행(字 形五行)을 도입하고 오행배속은 『훈민정음해례』에 준(準)할 것을 제안하였다.
Based on the Hunminjeongeum-unhae that Gyeong-jun Shin wrote in 1750, the method of assigning labials, ‘ㅁ(m)’ and ‘ㅂ(b)’, to the water elements and gutturals, ‘ㅇ(no phonetic value)’ and ‘ㅎ(h)’, to the land elements has been established as the majority opinion in naming science. However, the original promulgation of hangul, the Huminjeongeum-haerye, that was discovered in 1940, assigns labials, ‘ㅁ(m)’ and ‘ㅂ(b)’, to the land elements, and gutturals, ‘ㅇ(no phonetic value)’ and ‘ㅎ(h)’, to the water elements. To eliminate the confusion arising from the difference between the two versions, this study investigated the principles in the Five Element Assignment set forth in the Explication of Korean Phonology in connection with the study of Korean linguistics and examined the history and background of the Five Element Assignment in the Hunminjeongeumunhae in terms of phonology. As a result, it was found that Gyeong-jun Shin embraced Sug-ju Shin's recognition that Korean and Chinese phonological should be viewed differently, and the ultimate objective of the Hunminjeongeum-unhae lay in the ‘Phonological Map in Chinese Character’ in order to establish the connection with the phonological system of Chinese characters. Therefore, this study concluded that the method of Five Element Assignment as suggested by the Huminjeongeum-haerye is more appropriate for the following reasons: classifying phonemes according to the main purpose of creating Hangeul; to write Korean language (phonemes) in Korean alphabet, the tendency that phonemes are classified according to circumstances and times, and the phonological characteristics of modern Korean—the pronunciation of pure Korean and Chinese characters is the same. In addition, this study suggested the introduction of the Five Elements based hangeul characters since hangeul alphabet letters are derived from the movements or the shapes of the speech organs, and application of the Huminjeongeum-haerye for the Five Element Assignment.