Occasionalism is a philosophical doctrine about causation which says that created substances cannot be efficient causes of events. Instead, all events are taken to be caused directly by God. (A related concept, which has been called "occasional causation", also denies a link of efficient causation between mundane events, but may differ as to the identity of the true cause that replaces them.) The doctrine states that the illusion of efficient causation between mundane events arises out of God's causing of one event after another. However, there is no necessary connection between the two: it is not that the first event causes God to cause the second event: rather, God first causes one and then causes the other.
Islamic theological schools
The doctrine first reached prominence in the Islamic theological schools of Iraq, especially in Basra. The ninth century theologian Abu al-Hasan al-Ash'ari argued that there is no Secondary Causation in the created order. The world is sustained and governed through direct intervention of a divine primary causation. As such the world is in a constant state of recreation by God. In the Arabic language this was known as Kasb.
The most famous proponent of the Asharite occasionalist doctrine was Abu Hamid Muhammad ibn Muhammad al-Ghazali, an 11th-century theologian based in Baghdad. In The Incoherence of the Philosophers, Al-Ghazali launched a philosophical critique against Neoplatonic-influenced early Islamic philosophers such as Al-Farabi and Ibn Sina. In response to the philosophers' claim that the created order is governed by secondary efficient causes (God being, as it were, the Primary and Final Cause in an ontological and logical sense), Ghazali argues that what we observe as regularity in nature based presumably upon some natural law is actually a kind of constant and continual regularity. There is no independent necessitation of change and becoming, other than what God has ordained. To posit an independent causality outside of God's knowledge and action is to deprive him of true agency, and diminish his attribute of power. In his famous example, when fire and cotton are placed in contact, the cotton is burned not because of the heat of the fire, but through God's direct intervention, a claim which he defended using logic. In the 12th century, the Islamic theologian Fakhr al-Din al-Razi expounded upon similar theories of occasionalism in his works.
Because God is usually seen as rational, rather than arbitrary, his behaviour in normally causing events in the same sequence (i.e., what appears to us to be efficient causation) can be understood as a natural outworking of that principle of reason, which we then describe as the laws of nature. Properly speaking, however, these are not laws of nature but laws by which God chooses to govern his own behaviour (his autonomy, in the strict sense) — in other words, his rational will. This is not, however, an essential element of an occasionalist account, and occasionalism can include positions where God's behaviour (and thus that of the world) is viewed as ultimately inscrutable, thus maintaining God's essential transcendence. On this understanding, apparent anomalies such as miracles are not really such: they are simply God behaving in a way that appears unusual to us. Given his transcendent freedom, he is not bound even by his own nature. Miracles, as breaks in the rational structure of the universe, can occur, since God's relationship with the world is not mediated by rational principles.
In a 1978 article in Studia Islamica, Lenn Goodman asks the question, "Did Al-Ghazâlî Deny Causality?" and demonstrates that Ghazali did not deny the existence of observed, "worldly" causation. According to Goodman's analysis, Ghazali does not claim that there is never any link between observed cause and observed effect: rather, Ghazali argues that there is no necessary link between observed cause and effect.
Dualism
One of the motivations for the theory is the dualist belief that mind and matter are so utterly different in their essences that one cannot affect the other. Thus, a person's mind cannot be the true cause of his hand's moving, nor can a physical wound be the true cause of mental anguish. In other words, the mental cannot cause the physical and vice versa. Also, occasionalists generally hold that the physical cannot cause the physical either, for no necessary connection can be perceived between physical causes and effects. The will of God is taken to be necessary.