Denying the holiness of the Koran or the prophecies of Muhammad is straightforward apostasy. But Zarqawi and the state he spawned take the position that many other acts can remove a Muslim from Islam. These include, in certain cases, selling alcohol or drugs, wearing Western clothes or shaving one’s beard, voting in an election—even for a Muslim candidate—and being lax about calling other people apostates. Being a Shiite, as most Iraqi Arabs are, meets the standard as well, because the Islamic State regards Shiism as innovation, and to innovate on the Koran is to deny its initial perfection. (The Islamic State claims that common Shiite practices, such as worship at the graves of imams and public self-flagellation, have no basis in the Koran or in the example of the Prophet.) That means roughly 200 million Shia are marked for death. So too are the heads of state of every Muslim country, who have elevated man-made law above Sharia by running for office or enforcing laws not made by God.
Following takfiri doctrine, the Islamic State is committed to purifying the world by killing vast numbers of people. The lack of objective reporting from its territory makes the true extent of the slaughter unknowable, but social-media posts from the region suggest that individual executions happen more or less continually, and mass executions every few weeks. Muslim “apostates” are the most common victims. Exempted from automatic execution, it appears, are Christians who do not resist their new government. Baghdadi permits them to live, as long as they pay a special tax, known as the jizya, and acknowledge their subjugation. The Koranic authority for this practice is not in dispute.