This chapter discusses Josiah Royce's thoughts on monotheism. In the history of religion, monotheism, the doctrine that “there is one God,” or that “God is One,” is sharply opposed to a wide range of beliefs and teachings. However, in the history of philosophy, monotheism has a narrower range of contrasting or opposing beliefs. The philosophical problem of monotheism is, (1) in what sense is the world real? (2) In what sense is the world a rational order? (3) In what sense is the world ethical? The problem of monotheism requires a synthesis of all the three ideas of God, and an answer that is just to all three problems. Whether monotheism is true or not can be discovered only through a clear recognition of the contrast of the three ideas of God, and the synthesis which shall bring them into some sort of harmony.