The science of Kalām aims to prove the existence and attributes of Allah. For this purpose, the theologians adopted a method that turns from the sensible universe to the unseen universe. This method, named as qiyāṣ al-ğāib alā alā al-shāḥid, created a common ground in the discussions with the dissenters. Because the sensible universe is open to human perception in a way that does not allow for denial. From this point of view, the universe, which is defined as "everything other (...) than Allah" in Ashʿarite Kalām, has been discussed in terms of both structure and functioning. Based on the principles determined by the theologians, the universe is said to be composed of substance, accidents and bodies. The said entities are basically constructed in a way that is dependent on each other and on a higher will. Based on this construct, the Ashʿarite tradition preferred to explain the functioning of the universe with the theory of custom. In fact, their basic assumptions about the universe and Allah necessitated this preference. This is because they envision Allah as a fāil al- mukhtār deity with absolute will and power. Everything in the universe, except for the events or situations deemed impossible by the mind, is within His power. In this respect, the universe is described as an area of possibilities. The Ashʿarite tradition, which is based on the nonpermanent nature of accidents, insists that accidents should be recreated at every moment. This basic defense completely reveals the dependence of the universe on Allah. Built on these basic assumptions, the theory of custom uniquely explains the functioning of the universe without imposing any limitations on Allah, who has absolute will and power. This theory, which reflects the Ashʿarite tradition exactly, enables them to explain all theological issues, especially the relationship between Allah and the universe, in a consistent manner. This study aims to examine the basic principles that led the early Ashʿarite tradition to accept the theory of custom by analyzing them under several headings. For this aim, the views of the early Ashʿarite theologians have been identified through a literature review analyzed and interpreted in the context of the matter. (shrink)