For this purpose they placed at the basis of their speculations not the Aristotelian concepts of matter and form, the former uncreated and continuous, but adopted the atomistic theory of Democritus, denied the necessity of cause and effect and the validity of natural law, and made God directly responsible for everything that happened every moment in life. God, they said, creates continually, and he is not hampered by any such thing as natural law, which is merely our name for that which we are accustomed to see. Whenever it rains we are accustomed to see the ground wet, and we conclude that there is a necessary connection of cause and effect between the rain and the wetness of the ground. Nothing of the kind, say the Mutakallimun, or the Muʿtazila, the oldest sect of the school. It rains because God willed that it should rain, and the ground is wet because God wills it shall be wet. If God willed that the ground should be dry following a rain, it would be dry; and the one is no more and no less natural than the other. Miracles cease to be miracles on this conception of natural processes. Similarly the dogma of creation is easily vindicated on this theory as against the Aristotelian doctrine of eternity of the world, which follows from his doctrine of matter and form, as we shall have occasion to see later. The Muʿtazila were, however, chiefly known not for their principles of physics but for their doctrines of the unity of God and his justice. It was this which gave them their name of the "Men of Unity and Justice," _i. e._, the men who vindicate against the unenlightened views of popular orthodoxy the unity of God and his justice. The discussion of the unity centered about the proper interpretation of the anthropomorphic passages in the Koran and the doctrine of the divine attributes. When the Koran speaks of God's eyes, ears, hands, feet; of his seeing, hearing, sitting, standing, walking, being angry, smiling, and so on, must those phrases be understood literally? If so God is similar to man, corporeal like him, and swayed by passions. This seemed to the Muʿtazila an unworthy conception of God. To vindicate his spirituality the anthropomorphic passages in the Koran must be understood metaphorically.