在漢語區工作的外國商務人員，常會追問為什麼在商務英漢的交流或正式談判裡，Yes在會中或會後可能變成No。這種可能被解釋為欺騙的語言行為，其實可以有多項語用解釋。本文從語言的對話結構說明漢語的「是」並不完全對應英語的Yes，漢語的「是」在回答英語的問題時，是表示同意對方的說法，並不是回應英語的問話內容的肯定或否定。「是」還可以用來表達「我聽著，請繼續說」暫時自己不做決定的立場、遲疑的態度和「雖然」的轉折。「是」在有些場合也是用來彌補面子問題的回應詞，給予對方下臺的機會，並不是同意對方的說法。還有，過去十幾年，台灣出現沒有實質內容的「是」和「對」作為發語詞，有時還聽到說話人各處穿插這兩個詞語，用來彌補語流的空白。本文論述這類語言生活中的問題，並且從語用的觀點提出商務華語詞語教學建言。

Foreign business professionals working in Chinese-speaking regions often asked why in business English-Chinese conversations or formal negotiations, ＂yes＂ could turn into ＂no＂ right in the meeting or afterwards. Such a seemingly cheating language behavior in fact may have various explanations. This study explains in terms of dialog structure that the Chinese word ＂shi＂ does not correspond completely to English ＂yes＂. Chinese ＂shi＂ in answering English questions expresses the speaker’s agreement to what is said in the question and not to the positive or negative statement of the question sentence. ＂Shi＂ can also be used to indicate ＂I am listening, please go on＂ while undecided, hesitation, or concession. It is also used on some occasions as a response to save the face of the interlocutor and does not mean to agree with the person addressed. Moreover, in the past decade or so in Taiwan people used ＂shi＂ and ＂dui＂ as a non-sensical word in their conversation. They could be heard as speakers dotted the discourse with these words to fill the gap in the speech stream. This study discusses these pragmatic problems in language use. Some suggestions are raised for vocabulary teaching in business Chinese.