In theism, God is the creator and sustainer of the universe, while in deism, God is the creator, but not the sustainer, of the universe. Monotheism is the belief in the existence of one God or in the oneness of God. In pantheism, God is the universe itself. In atheism, God is not believed to exist, while God is deemed unknown or unknowable within the context of agnosticism. God has also been conceived as being incorporeal (immaterial), a personal being, the source of all moral obligation, and the "greatest conceivable existent". Many notable philosophers have developed arguments for and against the existence of God.