The Kratzerian tradition of modality assumes that obligation and permission are duals of each other. However, the question remains as to whether the notion of natural language permission is aptly represented. Anderson (1956) and von Wright (1968) develop a distinct sense of permission, namely strong permission, which conveys that performing an act is explicitly okay. According to this view, the fact that an act is not prohibited does not guarantee that it is permitted, hence the duality fails to hold. This paper presents evidence from Korean which suggests that Anderson and von Wright are on the right track. Korean utilizes conditional constructions and a special morpheme toy to express deontic concepts. I propose that toy is interpreted as a set of ideal worlds and show that the meaning of obligation can be compositionally derived from the meaning of this morpheme and conditionals. The compositional semantics of Korean permission, however, does not relate to deontic possibility. Rather, it conveys that an ideal state is reached irrespectively of performing an act. The connection between strong permission and the suggested interpretation is discussed, showing that Anderson and von Wright’s view of permission receives empirical support from natural language expressions.