This study limited the scope of examination to ‘乃則且’ to determine whether it is suitable to continue the ancient Korean language's use of conjunction or to keep the present parts of speech. The following are the findings of this study.1. Real and False Morphemes of ‘Adverbs’ in Ancient Korean and Definition of Adverbs1) Adverbs are Real MorphemesAdverbs are only used in adverbial phrases and adverbial phrases are not the major component of a sentence. Therefore, it cannot come alone in a sentence. Whether or not a phrase can come alone in a sentence is the absolute criterion of classifying real and false morphemes. 2) Definition of AdverbsAdverbs have real meaning, but are only used to describe technical terms (nouns, verbs, adjectives, and numerals), other adverbs, or other corresponding phrases, unlike verbs, adjectives, nouns, pronouns, and numerals are used as various components of a sentence. 2. Adverbial Use of ‘乃則且’The following are the definitions of ‘乃則且’ in Xianqin[先秦] -Lianghan[兩漢] Text.1) 乃Adverb [States a fact or additionally emphasizes a causality in a context].Pronoun [You]Postposition [Propositional Syllable].2) 則Adverb [States “nothing but” in a context of condition or causality or other contexts to emphasize the context].Noun [Rules, etc].Verb [State a rule]. Postposition [Interrogative Postposition].3) 且Adverb [States an addition of a fact]. Verb [Not paying attention]. Postposition.