Toshihiko Izutsu, the popular Japanese scholar of Islam, has based his work on semantic knowledge in his two valuable and famous books: God and Man in the Quran, and The Moral and Religious Concepts in the Quran. He has made a major breakthrough in the field of Quranic studies specifically the semantics of words and concepts in the Quran. In his book, The Moral and Religious Concepts in the Quran, Izutsu has extracted semantic relations of the major concepts of the Quran in a methodical manner using Saussure’s concurrency semantics. It is based on the acceptable scientific criteria such as, equivalence, substitution, antonymy, synonymy, morphology, derivations of words, and the meaning of each derivation in the Quran. He has further analyzed some of the most important moral concepts, particularly the concept of faith. In this paper, first, the principles of Izutsu in understanding of moral concepts in the Quran are identified. Then, the definitions of moral concepts and the fundamental dichotomy of morality in the Quran from Izutsu’s point of view are presented. Next, the definition of concurrency semantics and Izutsu’s methods of understanding moral concepts are explained. Finally, for the clarity of his method, his analysis of the word, faith is discussed as an example.