The purpose of this study is to analyze the polysemy of the connective ending '-어서(-eoseo)' in terms of cognitive linguistics. This corpus-driven study was conducted as the basis of sejong spoken corpus to understand the actual language usage patterns, and consequently ‘-어서(-eoseo)’, which has distinct four types of senses; ‘precedence’, ‘reason’, ‘background’, and ‘method’, and one indistinct sense ‘purpose’ is verified as polysemy. Moreover, it is confirmed that sense is not distinguished with clear boundary, but has continuous volumetric properties. ‘-eoseo’ has been extended into ‘reason’, ‘background’, and ‘method’ on ‘precedence’. As a result, this paper is understood the metonymy is act as a synchronization mechanism. Semantically, in this process, temporality is weakened gradually in semantically, and the syntactic constraint gradually eased.