This article proves to be a result of professional investigation contributing to studying on Islamic rationalism and also remarks on the period between the eighth and ninth century which would be an early period for rationalism, rather than its florescence in the twelfth century in Islamic philosophy. Investigating an early Islamic rationalism represented as ‘a theological school of Mu’tazilah’, the author attempts to sharply categorise and analyse, focusing on the concept of Kalām, a variety of effects derived from the meetings of Islamic and Greek philosophy. In addition he sheds light on the way to approach and to systematically understand active interaction between theology and philosophy of Islamic society in the Middle Ages. Despite these contributing factors, there could be still room for criticism. Firstly due to the fact that the author seems to allocate most of the contents in this article to a transitional history of concepts related to analogy and logical methodology, the essay loses sight on metaphysical themes, such as ‘anthropomorphism’ which should be significantly dealt with. Secondly, his argument on Kalām of the School of Mu’tazilah fully relies on the presupposition that the nature of God can be known by concepts and logical methods. Although this premise must have been a significant topic on Islamic rationalism in the specific period from the eighth to ninth century, it has been bitterly controversial on a general understanding of Islamic philosophy and society. Last but not least, this article pays considerable attention to continuity between Islamic and Greek philosophy only under the consistent impact of Aristotelianism. His partial approach necessarily results in a lack of revealing the essential feature of Islamic philosophy contrast to Greek one. This factor could be an Achilles’ heel. In sum, Islamic philosophy lies at the meddling place to be commensurable and incommensurable with Greek one. Arabic core ideas could be enough to share with Greek thoughts in pursuing the universal knowledge, on one hand, at the same time, both of them could be hardly common in that Islamic community had been strongly affected by its own faith relating to religious experience and mystery, on the other hand. Considering on both sides of speculative and cultic milieu in Greek culture, the article is only to emphasise the former, or theoretical and logical aspect, rather than the latter which played a crucial role in forming ancient Greek philosophy. For further studying on Islamic philosophy accessing to the mysterious and cosmological, Sufism should be excavated on the preferential basis.