卜辭「亦」字的用法歷來有三種說法，一是假為「夜」說；二是解為「再」、「又」說；三是釋作「也」。其中以後二說的影響最大，學者多從之。直到近來有學者重申「亦」假為「夜」之說，認為部分殷卜辭的「亦」仍應讀為「夜」。可見目前學界對於殷卜辭「亦」字的用法仍存在爭議。本文透過重新整理檢視卜辭的亦字句，認為卜辭「亦」字用法主要作為副詞使用，有的用為範圍副詞「也」；有的用作頻率副詞「再」、「又」。既可以用來表示兩件事的類同關係，也可以用來表示一件事或同性質事件的重複與繼續。殷卜辭目前尚未見一條完整而確切無疑可以讀為「夜」的「亦」字辭例。卜辭「亦」字是否有假為「夜」的用法，則仍需更多的證據證明。

There are three theories about the meaning of the character ”Yi” 亦 in the Shang Oracle-bone Inscriptions：1. ”Yie” 夜 (night); 2. ”Zai” 再 (again) and ”You” 又 (again); 3. ”Yie” 也 (too). The latter two theories have been more influential and widely accepted. But recently, some researchers are pointing out that the character ”Yi” 亦 should be read as ”Yie” 夜 (night). No definitive conclusion has been reached on the meaning of the character ”Yi” 亦. This study aims to re-analyze the dictions of ”Yi” 亦 in the Shang Oracle-bone Inscriptions. The character was mainly used as adverbs; sometimes as the range adverb ”Yie” (也), while other instances as the frequency adverb ”Zai” 再 (again) and ”You” 又 (again). However, there is little evidence of it being used as the time word ”Yie” 夜 (night).