This paper aims to discuss the contrast, contrastive topic, and contrastive focus in Korean sentences. First of all, the contrast in the sentence can be expressed by the particle ‘un/nun’. If the particle ‘un/nun’ is combined with the topic and the focus in information structure, it can be the contrastive topic and contrastive focus respectively. However, the contrastive topic and contrastive focus are applied differently in linguistic papers. The particle ‘un/nun’ can express two functions. One thing is the topic and the other thing is the contrast in the sentence. When it uses the topic in the sentence, it locates to the beginning of the sentence and combines with the anaphoric or genetic reference. However, when it uses contrast in the sentence, it locates not to the beginning of the sentence. It makes the alternative sets express the meaning of implicature and the noun phrase with the particle ‘un/nun’ would form the latent phrases. Meanwhile, the particle ‘un/nun’ cannot become the topic in the dependent clauses. Secondly, the contrastive topic, it locates at the beginning of the sentence and combines with the particle ‘un/nun’. It expresses the contrastive meaning when the responsive clause appears continuously. There is a case that the question is to give all members but the answer is to give an element among them. It makes to express the contrastive meaning by the latent members. However, it is not a contrastive topic, because it needs more information to develop the efficiency of the conversation. Thirdly, there are two opinions in contrastive focus. One is the exhaustive-listing that expresses the contrastive focus, it would combine with the case-marking particle. The other is to combine with the particle ‘un/nun’ to express the alternative set of implicature meaning. In this paper, I advocated that the former opinion is more accurate according to the linguistic view. In the latter opinion, it is not the focus but the exclusive implicature through latent alternatives.