Traditional human communities believe that truth leads to salvation, and error to damnation. It is probable that very many religious people in a variety of denominations still believe this. Historically, religiously-faithful princes have therefore seen it as necessary to use the coercive power of the state to forbid apostasy. One of the most powerful and persistent manifestations of this understanding in history was the Inquisition, which was definitively abolished in 1834. Protestant countries also respected this drastic principle; in fact, the first converts to Islam in Britain were impaled on stakes. In a Hindu context, ‘apostasy’ was often classified as violation of caste rules and boundaries, and similarly drastic consequences could follow. After the Mongol sack of Baghdad in 1253, Buddhists who converted to Islam were routinely put to death.

The four canonical schools of Sunni Islamic law, and also most pre-modern Shi’a jurists, recommend similarly drastic penalties, although the judge is enjoined to ‘look for ambiguities’ in order to avert the death penalty wherever possible.

The Ottoman Caliphate, the supreme representative of Sunni Islam, formally abolished this penalty in the aftermath of the so-called Tanzimat reforms launched in 1839. The Shaykh al-Islam, the supreme head of the religious courts and colleges, ratified this major shift in traditional legal doctrine. It was pointed out that there is no verse in the Qur’an that lays down a punishment for apostasy (although chapter 5 verse 54 and chapter 2 verse 217 predict a punishment in the next world). It was also pointed out that the ambiguities in the hadith (the sayings of the Prophet) suggest that apostasy is only an offense when combined with the crime of treason. These ambiguities led some medieval Muslims, long before the advent of modernisation, to reject the majority view. Prominent among them one may name al-Nakha’i (d.713), al-Thawri (d.772), al-Sarakhsi (d. 1090), al-Baji (d. 1081), and al-Sha’rani (d.1565). The debate triggered by the Ottoman reform was continued when al-Azhar University in Cairo, the supreme religious authority in the Arab world, delivered a formal fatwa (religious edict) in 1958, which confirmed the abolition of the classical law in this area.

Among radical Salafis and Wahhabis who do not accept the verdicts of the Ottoman or the Azhar scholars, it is generally believed that the majority medieval view should still be enforced.

The best discussion of the controversy is the book by Mohammed Hashim Kamali, “Freedom of Expression in Islam” (Cambridge, 1997).