本文從語言演化的動因角度出發，通過對雲南諸方言和山東文登、榮成方言表面看似雷同的「去顎化」現象的分析，說明了前者是由系統內有語音條件的音變引起的，後者是由系統外其他成分接觸引起的。兩者雖然表相一致，但是觸發機制是不同的。進一步論述了語言演化中，內外兩種機制的複雜關係，並明確釐析兩者的重要性。

The focus of this paper is de-palatalization in Chinese dialects. Based on an analysis of Yunnan and Shandong dialects, we argue that there are two different types of motivation triggering de-palatalization. The first type stems from internal factors, and may be regarded as caused by within-language conditions; the second type is due to external factors, and may be regarded as caused by language contact. Although the two types appear similar, they are triggered by different mechanisms. This paper also discusses the complex relationship between the trigger mechanisms of internal and external types during language evolution, while clearly identifying the importance of both types.