Why is mutual understanding between two substantially different comprehensive language communities often problematic and even unattainable? To answer this question, the author first introduces a notion of presuppositional languages. Based on the semantic structure of a presuppositional language, the author identifies a significant condition necessary for effective understanding of a language: the interpreter is able to effectively understand a language only if he/she is able to recognize and comprehend its metaphysical presuppositions. The essential role of the knowledge of metaphysical presuppositions (...) in understanding is further strengthened by developing a truth-value conditional theory of understanding. It is concluded that if the interpreter approaches an incompatible alien language from the standpoint of the interpreter's own language by projecting the metaphysical presuppositions of his/her own language upon the alien language, then the mutual understanding between the two language communities is doomed to failure. (shrink)