作者主張古漢語除了一般所構擬的三套塞音聲母（不送氣不帶音、送氣不帶音、帶音）外，還具有三套冠鼻音聲母；這些聲母的冠鼻音成分來自前綴N-。前綴N- 具有將及物動詞轉換為不及物動詞的作用，並且在附加過程中使詞根不帶音不送氣的阻塞音聲母變為帶音。冠鼻音聲母後來消失了，只留下中古漢語著名的及物動詞伴隨不帶音阻塞音聲母與不及物動詞伴隨帶音阻塞音聲母的交替。然而，只有詞根聲母為不帶音不送氣時才會使聲母帶音；冠鼻音化的送氣不帶音聲母並不受影響，它們發展為中古漢語的送氣塞音。作者並提出語音變化的年代學。早期借至苗瑤語的漢語借詞的證據亦在討論之列。不及物的N- 前綴與許多藏緬語言的不及物鼻音前綴表現出對應關係──儘管書面藏語的a-ch'ung（也是個鼻音前綴）與此N- 前綴因功能不同而無法對應。本文並提出漢藏語言的不及物鼻音前綴可溯源至原始漢藏語的不及物m- 前綴。中古漢語不及物帶音與藏緬語著名的「詞根聲母交替」（同樣為及物動詞伴隨不帶音聲母與不及物動詞伴隨帶音聲母的對比）在形式和功能上的相似引發了藏緬語此類交替的來源的問題。漢語的交替既已證明來自於鼻音前綴，則藏緬語的交替似亦不無可能。不過，這個問題目前暫時不下定論。

　　　　　The author argues that in addition to the three series of stops commonly reconstructed (voiceless unaspirated; voiceless aspirated; voiced), Old Chinese possessed three prenasalized series, in which the prenasal element was a prefix N-. This prefix changed transitive verbs to intransitives, voicing a voiceless unaspirated obstruent root initial in the process. Prenasalization later disappeared, leaving behind the well-known Middle Chinese alternation between transitive verbs with voiceless obstruent initials and intransitive verbs with voiced obstruent initials. Voicing, however, occurred only if the root initial was a voiceless unaspirated obstruent: prenasalized voiceless aspirated initials were not affected: they evolved to Middle Chinese aspirated stops. A chronology of phonetic changes is proposed. Evidence from early Chinese loans to Miao-Yao is discussed. The intransitive N- prefix is shown to correspond to intransitive nasal prefixes in various Tibeto-Burman languages; while the connection to Written Tibetan a-ch'ung, also a nasal prefix, is regarded as spurious on functional grounds. It is proposed that the intransitive nasal prefixes in Sino-Tibetan languages go back to a proto-Sino-Tibetan intransitive m- prefix. The formal and functional similarity between intransitive voicing in Middle Chinese and the alternation known as "alternation of root initial" in Tibeto-Burman languages, which likewises contrasts transitive verbs with voiceless initials and intransitive verbs with voiced initials, raises the issue of the origin of this alternation in the Tibeto-Burman languages: considering that the Chinese alternation has turned out to have its origin in a nasal prefix, is the same also true of the Tibeto-Burman alternation? The question is for the moment left open.