 All Ash’arite theologians up to the generation of al-Ghazâlî—including his teacher al-Juwaynî—subscribed to the occasionalist ontology developed by al-Ash’arî. One of al-Juwaynî’s late works, the Creed for Nizâm al-Mulk (al-‘Aqîda al-Nizâmiyya), shows, however, that he already explored different ontological models, particularly with regard to the effects of human actions (al-Juwaynî 1948, 30–36; Gimaret 1980, 122–28). A purely occasionalist model finds it difficult to explain how God can make humans responsible for their own actions if they do not cause them. As a viable alternative to the occasionalist ontology, al-Ghazâlî considered the Avicennan model of secondary causes. When God wishes to create a certain event He employs some of His own creations as mediators or “secondary causes.” God creates series of efficient causes where any superior element causes the existence of the inferior ones. Avicenna stresses that no causal series, in any of the four types of causes, can regress indefinitely. Every series of causes and effects must have at least three components: a first element, a middle element, and a last element. In such a chain only the first element is the cause in the real sense of the word (‘illa mutlaqa) of all subsequent elements. It causes the last element of that chain—the ultimate effect—through one or many intermediaries (singl. mutawassat), which are the middle elements of the chain. Looking at a chain of efficient causes, the “finiteness of the causes” (tanâhî l-’ilal) serves for Avicenna as the basis of a proof of God’s existence. Tracing back all efficient causes in the universe will lead to a first efficient cause, which is itself uncaused. When the First Cause is also shown to be incorporeal and numerically one, one has achieved a proof of God’s existence (Avicenna 2005, 257–9, 270–3; Davidson 1987, 339–40).