人是否能認識神的本質，是十三紀爭論激烈的問題之一。代表東方希臘傳統的狄奧尼修斯(Dionysius Areopagite)，強調神之超越與不可知，而西方以奧斯定為主的傳統，則主張人在現世對神就有某種知識。多瑪斯以他一貫的舊論新說的方式，主張人對神最高的知識，是認識神不是什麼；這是一條《否定之路》(via negativea)，多瑪斯也稱為《分離之路》(via remotionis)，以除去人之知識，在認識神時所造成的障礙，故可稱為《去障之路》(the apopathic way)。當西方傳統理解神是「自有者」時，將希臘傳統之本體論，與基督宗教的神學融合。多瑪斯是神神學的架構，探討人認識能有實現之條件與限制，而《去障之路》是一條由理性而通達信仰之路，屬於「密契神學」(Mystical Theology)，但從方法而言則屬於形上學。本文首先說明多瑪斯對神學之看法，其次是從人對神本質的認識問題，而討論《去障之路》，最後是分析多瑪斯《去障之路》之思想。

　　　　　One of the much debated problems of the thirteenth century, is the question of knowing the essence of God. According to Greek tradition tradition represented by Dionysius the Areopagite, God transcends all things and the best way to know God is the negative way. Augustinain tradition, on the other hand, affirms that human beings have some knowledge of God's essence, even in this world. Thomas Aqinas, in his usual creative synthesis, states that the best knowledge human being can have on earth is to know what God is not. According to him, human being begins by knowing God's existence through the way of causality, then affirming the supremacy of God by way of excellence, and finally by way of negation because God transcends all. The negative way. It is the contention of this paper that when god revals himself as he who is, and Christian thinkers understood it as Being, ancient Greek ontology, Christian philosophy and spirituality become one. Though Aquinas investigates the conditions and limit of human knowledge within the theological framework, the method he uses, is one of metaphysics, and the negative way is the way of Mystical Theology. This paper is divided into three parts: (1) Aquinas's notion of theology; (2) whether it is possible for human being to know the essence of God; (3) nature of the apophatic way.