后代发“zh-,ch-,sh-”一组后舌叶音(旧称舌上音)声母的字,在上古是念成“d-,t-”等舌尖音(旧称舌头音)声母的,反映在中古音的“三十六字母”中,是“知彻澄娘”四纽归于“端透定泥”.清代古音学家钱大听在《十驾斋养新录》中把这一规律称为“古音舌头、舌上不分”. 这一规律的讲明,对于我们阅读古籍很有帮助.如“直”古不在“澄”母而在“定”母,“中”古不属“知”母而属“端”母,因此它们在古籍中常和其他字通假,使用得较灵活.如: The descendant of “zh-, ch-, sh-” a group of tongue leaf tone (formerly known as tongue sound) consonants of the word, in ancient times is read as “d-, t-” and other tongue sounds (formerly tongue tone) initials Is reflected in the “thirty-six letters” of the Middle Gu Yin, which is the result of “knowing the bride and grooming.” In the Qing Dynasty, the ancient phonologist Qian Dazhan put “ This law is called ”the ancient tone tongue, the tongue does not divide.“ This rule of explanation, for our reading of ancient books is helpful .As the ”straight“ ancient ”Cheng“ Since ancient times belong to the ”mother“ of the mother rather than the mother of ”knowledge," they are often used more frequently in ancient books as other words,