It has been observed that the trigger and target in labial harmony are sometimes required to share a particular feature. Working within the framework of Radical CV Phonology, I argue that labial harmony is always subject to further requirements, stated in terms of additional licensing relations. Radical CV Phonology uses a limited set of elements that can be involved in such licensing, resulting in a restricted typology of labial harmony. Furthermore, I propose a distinction between lexical elements, which are always visible, and elements derived through harmony, which become visible in cycles. Crucially, elements derived through labial harmony do not have access to elements derived through tongue-root harmony, thus accounting for the lack of labial harmony in high vowels in tongue-root harmony systems. This architecture also accounts naturally for the behaviour of /i/, which is opaque to labial harmony in Tungusic languages but transparent to labial harmony in Mongolic languages.

中文翻译：

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突厥语、通古斯语和蒙古语的唇音和谐：一种元素方法

据观察，有时需要唇音和谐的触发器和目标来共享一个特定的特征。在 Radical CV Phonology 的框架内工作，我认为唇音和谐总是受制于进一步的要求，就额外的许可关系而言。Radical CV Phonology 使用了一组有限的元素，这些元素可以参与此类许可，从而导致唇音和谐的类型学受到限制。此外，我提出了词汇元素之间的区别，它们总是可见的，而通过和声衍生的元素在循环中变得可见。至关重要的是，通过唇音和声衍生的元素无法访问通过舌根和声衍生的元素，从而解释了在舌根和声系统中高元音中缺乏唇和音的原因。