noun
the four tones of Middle Chinese
Technical term in Chinese historical phonology referring to the four tone categories: 平声 (level), 上声 (rising), 去声 (departing), and 入声 (entering).
平上去入は中古中国語の四声を表す用語です。
平上去入 is a term for the four tones of Middle Chinese.
四声 is a broader term for 'four tones' and can refer to tone systems in modern Chinese dialects as well, while 平上去入 specifically names the traditional Middle Chinese categories.
From the names of the four tone categories in Middle Chinese: 平 (level), 上 (rising), 去 (departing), and 入 (entering).