One of the functions of philosophy of education is to investigate the aims of education profoundly. Rationality has been the core concept of educational ideals since the era of Enlightenment. However, many scholars is going to reject or revise the concept of rationality in the postmodern age. H. Siegel defended rationality as an aim of education by insisting the certainty of knowledge and refuting relativism. N Burbules, on the other hand, proposed reasonableness to replace rationality as the educational aim by absorbing the spirit derived from postmodernity. The purpose of this article is to discuss the arguments about rationality in education between Siegel and Burbules. The author concludes two implications in the end. On the one hand, based upon the context of educational argument, which means educators to conform, investigate, reflect philosophical claims in educational contexts, the author thought the reasonableness proposed by Burbules was more comprehensive than rationality by Sigel as an educational aim. However, on the other hand, the author agrees that the rationality argued by Siegel, in terms of better reasons for choice, was more suitable in the political, economic, and educational contexts of Taiwan. The rationality of reasonableness is still an important issue to investigate further m Taiwan.