The issue of jawhar and ‘arad (substance and accidents), which are discussed by the mutakallimūn (kalam scholars) while they criticize Christianity, especially in the context of the trinity, is important due to Christian’s understanding of jawhar. Juwaynī (d. 478/1085) is one of the scholars who discussed jawhar and ‘arad expansively while criticizing Christian beliefs. This article examines Juwaynī’s argu- ments about Christian creeds, such as naming God as a jawhar, trinity, and incarnation tenets. It fo- cuses on arguments which are related to jawhar and ‘arad. In order to make the connection between critiques more visible, the article also addresses Juwaynī’s understanding of jawhar and ‘arad, and the cosmological principles that he accepts. The main aim of the article is to give an example of how the cosmological principles of kalām affect mutakallimūn’s methods while they were defending Islam against other religions and doctrines, and how they reflect the theological issues in the case of Juwaynī. In this regard, the article discusses the concept of the trinity and the Christian conflicts about it. Then it handles the main topic and methods that Muslim scholars grounded on while they were criticizing Christianity. Finally, it discusses Juwaynī’s critiques against Christian beliefs. In this way, it aimed to reveal the similarities and differences between Juwaynī and other early period mutakallimūn’s critiques and to present a better understanding of Juwaynī’s criticizing method.