The first two thirds of the work cover the medieval scholars, with Ghazalli as a centre. Basic questions are addressed first. Does the duty to forbid wrong apply to women and slaves, and do scholars have special obligations? Most were reluctant to "limit the pool of potential forbidders of wrong in any very drastic way". Is there a duty to forbid rulers and parents? What happens when law schools disagree about what is wrong? Some divided "right" into "obligatory" and "commendable", but allowed no such division of "wrong"; others argued more symmetric positions. And there was a fairly general restriction of the duty to include only prevention, reserving punishment to the state.
How is wrong to be forbidden? The "hand, tongue, heart" three-fold scheme was widely used, though Ghazalli's system doesn't mention the heart and extends to the recruitment of armed bands. Another option is the avoidance of the duty, by emigrating or otherwise avoiding situations likely to bring one into contact with wrongdoing.
What restrictions are there on the obligation? There were many different schemes here, but four common though debated requirements are knowledge (of both the law and the fact), efficacy, an absence of worse side-effects, and the absence of danger. Some concerns for privacy are also evident, though these tend to be procedural rather than substantive: prying is wrong and private rebuke is to be preferred to public shaming.
Rulers naturally appealed to the rhetoric of forbidding wrong and many scholars were prepared to grant them a monopoly on the use of violence to forbid wrong. Others were much more negative: "Cases where Ibn Hanbal is prepared to countenance recourse to the state are rare indeed. ... [his] reserve thus arises from the arbitrary and unpredictable character of political power".
Stories of the misdeeds of rulers and their rebuking, typically by scholars, are common. But sometimes the rulers come off better, as in a famous exchange between a caliph and zealot, and many scholars are critical of Ghazalli's enthusiasm for rebuking rulers. Scholarly opinion is "heavily stacked" against rebellion as a way of forbidding wrong, though there is a minority activist tradition.
After the first two centuries of Islam, there were no outright denials of a duty to forbid wrong. Many Sufis downplayed but did not reject the duty, while Abd al-Ghani came closest to denying it, arguing that enforcement was a prerogative of the authorities and that unachievably pure motives were needed before action. In any event, "none of the basic ideas in these responses come from outside the standard repertoire of Islamic values".
Most of our sources on forbidding wrong are scholars and the examples they discuss are mostly puritanical, involving drink, women, and music. There is no sign that lay people did much forbidding, or that it was an ordinary part of life. But while anecdotes of scholars confronting rulers may reflect literary trope more than historical reality, appeals to "forbidding wrong" in justifying rebellion are well attested.
Forbidding wrong has taken on new forms in modern times, with notable differences between the Sunnis and the Imamis (the major Shiite sect). "Among the Sunnis ... new thinking cannot easily take place within the framework of the scholastic heritage; instead the locus of intellectual creativity necessarily shifts outside it." With their "markedly more rationalist heritage", Imami scholars "have attacked and gone beyond the traditional view of the conditions of obligation", and innovated in other ways.
In response to the West, some have deployed forbidding wrong in the service of human rights. Organisations have taken on a new significance and the role of the state has remained a central concern, with a fundamental tension between activism and quietism. Surprisingly, the radical Sayyid Qutb went "farthest in modern times towards voiding the duty of the individual to forbid wrong", while Khomeini and other Imami clerics have introduced more activist ideas into a traditionally quietist tradition. Cook describes religious policing in Saudi Arabia and looks in detail at one Imami, Islami, who has emphasized traditions protective of privacy.
Similar phrasing and ideas occur in many religions, but systematic elaboration is rare: there are parallels in Rabbinic Judaism and medieval Catholicism ("fraternal correction") but not in Zoroastrianism, Buddhism, or Confucianism. Cook considers the possibility that the three monotheist traditions are linked, and possible continuities with pre-Islamic Arabia. But Islam is unique in having mainstream endorsement of a duty that is universal and has a "marked potential for violence, subversion and egalitarianism".
Forbidding Wrong in Islam opens with a news story about a woman being raped on a Chicago station and the response of the bystanders; it ends with the closest parallel in Western thought, the philosophical and legal debate over "rescue". Two central differences between the traditions lie in the standing of God in human affairs and the possibility of victimless wrongs.
Though Cook maintains a narrow focus, never venturing into a broader account of Islamic ethics, the substantive content of the tradition he follows is involving. Forbidding Wrong is most valuable, however, as a case study of change and continuity in Islamic thought and of differences between the branches of Islam and its schools of law and theology. It includes a brief introduction to those, and to sources and terminology, but while it could be followed by readers without much knowledge of Islam it would work best as a supplement to a more general history. Forbidding Wrong in Islam is a thematic summary of a longer work Commanding Right and Forbidding Wrong in Islamic Thought, page numbers in which are given as references.