||Oh, Hyo-Jung & Kim, Chonghyuck. (2021). On the usage patterns of the Korean prefix kay- on Twitter. The Linguistic Association of Korea Journal. 29(1), 1-23. A few researchers have recently claimed that the prefix kay-, which literally means dog, has undergone a dramatic change over the past decade. Before the change, kay- was severely confined in terms of its syntax and semantics; it was restricted to combine with a handful of nouns, and semantically, it had the sole function of adding or boosting the negative sense of its host. Kay- is no longer used as such. It can virtually combine with a host of any category which has gradable meaning, as its semantics has acquired the function of an emphatic marker like very. A linguistic change is driven by the people who use it. As the number of people who adopt and use the new features of a linguistic item grows, the chance of its survival as a transformed linguistic entity increases. Thus, it is important to examine in a precise manner how kay- is used in order to track the course of change it has gone through in the past and to predict its survival in the future. No such effort, however, has been made so far. In this article, we show that we can obtain an extensive amount of data showing the real time usage of kay- over the past decade using techniques developed in informatics and that kay- has indeed undergone a dramatic change, as reported by other researchers. We also show, by analyzing the data extracted from tweets tweeted during the 48 hours, that kay- is much more frequently used in comtemporary Korean in the new pattern than in the old pattern, a concrete piece of evidence to back the claim that kay- is productively used.