For some in the Middle Ages any appeal to the autonomy of nature, that is, any appeal to the discovery of real causes in the natural order, seemed to challenge divine omnipotence. One reaction, made famous by some Muslim thinkers, known as the kalam theologians, was to protect God's power and sovereignty by denying that there are real causes in nature. Thus, they would say that when fire is burning a piece of paper it is really God who is the true agent of the burning; the fire is but an instrument. Accordingly, events that occur in the natural world are only occasions in which God acts.