Choi, Choong-Lyeol(1995). Presuppositions in the study of presupposition. Linguistics vol. 3. The aim of this paper is to explain presupposition on the basis that our language ultimately contributes to the expansion of our cognitive world. We examine the semantic and pragmatic definitions and show their defects with concrete examples in English. And we inquire into some prerequisites for the proper treatment of presupposition ; cognitive principle, felicity condition and context. With the help of those concepts, the presupposition can be explained well together with its cognitive definition : when A is true in contexts which can be connected to a speaker, a hearer or both of them, B presupposes A if B or the utterance of B is felicitous.