"Mood" is an inseparable concept from "modal particle", which is a form of mood.
首先，“语气”是与“语气词”息息相关的一个概念，“语气词”只是“语气”的一种体现形式。
参考来源 - 元杂剧语气词研究
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Modal particle
abstract:In linguistics, modal particles are always uninflected words, and are a type of grammatical particle. Their function is that of reflecting the mood or attitude of the speaker or narrator, in that they are not reflexive but change the mood of the verb.