The purpose of this essay was conducting the study on what the tautologic expression’s perfunctory and semantic characteristics were, and then, offering specific feature of the pragmatics, figuring out what the key(focused) element, which a speaker tries to display, with the highest information-transfer capability of that expression was. In addition to this, what impression speaker’s intension of utterance bears and how a listener infers accurately that of speaker were explained, as well as pragmatic strategy for ‘N+是+N’ was examined. The conclusion is that the patterns of meaning of the ‘N+是+N’ are 7 kinds such as singularity, subordinateness, individuality, equal status, progressiveness, impartation and representability. The 7 strategies for utterance for the ‘N+是+N’ are; Enlightenment; Admonition; Favor; Undeniableness; Sureness; imperativeness; and overstatement. It can be said that tautology is an utterance which a speaker uses intentionally in a context and also is a context-dependant expression which a listener will, by way of presupposing conceptual information and background knowledge, choose the meaning of the utterance thus interpret it in accordance with the context Through these investigations, the essay looked over many different aspects of tautologic ‘N+是+N’. And that’s all for this study with remaining of comparison between tautologies expressed in Korean and Chinese or further study on other sort of words to be conducted later.