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商务信函写作遵循7C原则，即清晰(Clearness)、简洁（Conciseness）、准确（Correctness)、具体（concreteness）、周到（Consideration）、礼貌(Courtesy)以及完整(Completeness)。
下面将对这七大写作原则逐一进行详细说明：

清晰(Clearness)
这一写作原则要求写信人必须清楚写信的目的，确保收信人能够完全理解写作者所要表达的意思，不会产生误解。语言表达力求清楚简练，切忌使用复杂的短语及句式。
简洁（Conciseness）
用最少的语言表达最丰富完整的内容。在行文过程中尽量选用简单常用、易懂、朴素的词汇，采用简洁，直接的句子，提高沟通效率。
准确（Correctness)
准确无误是商业英语信函写作中最最要的原则。
准确原则不仅仅指单词拼写、标点符号无误，语法、结构格式正确，还应确保信函所涉及的信息、数字、事实准确无误。
因此，在进行商业英语信函写作中应反复审核相关信息，如：收信人的职称、姓名、地址、交货时间、地点、货物品质、颜色、尺码、单价、总价、包装等。

具体（concreteness）
具体原则是指信函中涉及的内容、信息要详实具体、丰富生动，表达要完整。
商务信函写作中要注意避免类似：soon, good, nearly 等含混不清的表达方法。错误示例：I will send the samples to you soon. 正确示例： I will send the samples to you next Monday.
周到（Consideration）
写信人要有读者意识，也就是能站在对方的立场全面考虑问题，理解并照顾对方的愿望，需求和感受，正面、肯定的谈问题，尽量避免重否定角度谈。
在商务信函的写作过程中，应从对方的角度考虑问题，考虑对方的处境，并预测对方接收到信函的反应，即写作时采用you-attitude而不是we-attitude.
礼貌(Courtesy)
礼貌原则不仅仅体现在使用 Please, thanks you 等这些常规词汇上面，在书写过程中需注意把握行文思路。
要遵守国际商务往来惯例；尊重对方风俗习惯；语言表达要客气有分寸，避免使用命令口气；多用友好、肯定的语气，批评建议时尽量用委婉语气，回复信件要及时。

完整(Completeness)
商务信函应该提供所有必要的信息，使所有相关事件得到阐明和论述，相关问题得到答复和解释。
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