This book is a treatise on Middle Korean, i.e. native Korean words and Sino-Korean words.

This book adopts as original texts two Middle Korean translations of the Twu-Chang-Kyeng-Hem-Pang (痘瘡經驗方) and the Nap-Yak-Cung-Chi-Pang (臘藥證 治方), which were medical books in the Joseon Dynasty. Dr. Yeong-Seop Park argues that these medical books are important research materials for studies of Middle Korean in the sense that in those days medical books written in classical Chinese were translated into simple words in order to disseminate medical knowledge that ordinary people needed. Furthermore, it selects the following texts as supplementary research materials: (1) an anthology Twu-Si-En-Hay (杜詩諺解) 'the Middle Korean translation of Po Twu (杜甫)’s poetry', (2) three Buddhist scriptures 'Sek-Po-Sang-Cel (釋譜詳節) ', 'the Middle Korean translation of the Nung-Em-Kyeng (楞嚴經)', and 'the Middle Korean translation of the Nam-Myeng-Chen-Kyey-Song (南明泉繼頌)', (3) three handbooks of Chinese characters for children, i.e. 'Hwun-Mong-Ca-Hoy (訓蒙字會)', 'Yu-Hap (類合)', and 'Chen-Ca-Mwun (千字文)'.

This book makes a comparative analysis on Middle Korean equivalents for Chinese characters of the above texts. This analysis shows the following two results. One is how one Chinese character is translated into multiple Middle Korean native words according to contexts. The other is the phenomenon of disappearance of Middle Korean words. This phenomenon results from the competitive relationship between/among synonymous Middle Korean native words or between/among synonymous Middle Korean native words and Middle Sino-Korean words.