This article endeavours to show the compatibility of significant trends in the largest Islamic theological school, namely the Ash‘ari, with the authority of reason in ethics. On the one hand, this authority requires reason to understand moral values while, on the other, proving that this authority does not conflict with the creation of actions by God. Ash‘arism has accepted the ability of reason to understand moral values, while also accepting practical reason. Moral values and their antithesis are examples of good and evil and can be understood by rational reasoning. Nevertheless, Ash‘arism also regards acts as the creation of God, yet without negating the ability of reason to understand good and evil. This article explains the differences between the Ash‘arites and Mu‘tazilites regarding the authority of independent reason in ethics. The negation of the ability of reason to discern God's acts and commands, thereby accepting the need for religion, has made the Ash‘arite theological school unique. Accordingly, religion and reason are the two references in ethics within this school. This article concludes that the authority of reason is compatible with Ash‘arism if we base our reading on the view of many prominent Ash‘ari scholars. Furthermore, this foundation could be used to study the compatibility of Islam with modern ethical theories.