The muslim judgement against apostates has in recent years been applied in cases of publicly expressed conviction that contradict generally accepted foundations of the Muslim faith. This situation is, however, only the outcome of a theological and legal development in the 5th/11th century. Until that time, the judgement of apostasy (irtidād) could not have been applied against Muslims who voiced opinions that were regarded as unbelief. The rules for this earlier period were written down by al-Shāfi‘ī in his Kitāb al-Umm. His interpretation of the legal institution of istitāba leads to the acknowledgement that the judgement of irtidād is applicable only in a very small number of cases. This reflects legal sensitivity in the period of mass conversions when the secret practice of pre-Islamic religious rites amongst newly converted Muslims might have been widespread. Al-Shāfi‘ī's guidelines, based on earlier judgements within the Kufan tradition, gained widespread acceptance in the Hanafī, Hanbalī, and Shāfi‘ī schools of law. A first change can be noted in the middle of the 5th/11th century when authors such as al-Māwardī and Abū Ya‘lā argued for a less generous application of the istitāba. Two generations later, al-Ghazālī (d. 555/1111) and his contemporaries such as Ibn ‘Aqīl (d. 513/1119) did not restrict the judgement of irtidād to cases of openly declared apostasy. Al-Ghazālī develops a reasoning which is fully aware of the change in law and of the deviation from long-established principles. His own condemnation of three key statements of the falāsifa, expressed in his Tahāfut al-falāsifa, would be impossible without his identification of kufr with irtidād in earlier works.