Whether or not the ‘-(eu)ro’ Kasus phrase as a sentence constituent is indispensable is fundamentally related with the argument structure of verb. That is to say, it means whether the ‘-(eu)ro’ Kasus phrase is syntactically required or not. But in spite of such cognition, it is really hard that we judge whether it is true or not. Therefore, I approach the problem through picking out the constituent which has semantically adjunct function. Then, the word order has to be considered. With the result, the ‘-(eu)ro’ Kasus phrases of the functions such as via, cause or reason, sense or value, instrumental, material, time or space background, norm, spacial background, and the ‘-(eu)ro’ Kasus phrases or the ‘-eseo’ Kasus phrases which express semantically equal meaning with NP of ‘NP+ha-’ construction or with Subject NP of verb ‘byunha-’ construction, and the idiomatic ‘-(eu)ro’ Kasus phrases or ‘-(eu)rosseo’ Kasus phrases, etc. are all estimated as the adjuncts. But the ‘-(eu)ro’ Kasus phrases of the functions such as goal, result or product, status property, and those related to time in the verb ‘(jeong)ha-’ construction, etc. are all estimated as the arguments. If such ‘-(eu)ro’ Kasus phrases are adjuncts, then they have a modifier scope individually such as adverb. It is deeply related with the unmarked positions of those. According to such description some adjuncts modify the lexical category, some adjuncts modify the sentence category, some adjuncts modify the mediate category which is larger than the lexical category but is smaller than the sentence category. However, idiomatic ‘-(eu)ro’ Kasus phrases or ‘-(eu)rosseo’ Kasus phrases are always the sentence category adjuncts, but ‘-(eu)roseo’ Kasus phrases in front of the sentence are not only those but also the ‘situation presentive word’ related to topic.