In 1092 the Vizir Nizam al-Mulk, patron and protector of Abu Hamid al-Ghazali, was murdered by an agent of the Isma'ili movement. Three years later, al-Ghazali withdrew from his chair at the Nizamiyyah in Baghdad to rebuild his theology from its foundations. Al-Qistas al-Mustaqim, The Just Balance, belongs to that later period: a short, deliberately argued response to the central claim of the Ta'limiyyah, the activist wing of the Isma'ilis associated with Hasan-i Sabbah and the fortress of Alamut, that religious truth can be known only through an infallible Imam.
D.P. Brewster's translation, prepared at the University of Canterbury and first published in 1978, is the only English rendering of this work; Western scholarship had previously known it solely through Father Victor Chelhot's French edition. The book unfolds as a dialogue between al-Ghazali and an unnamed Ta'limi interlocutor, who challenges him to justify his knowledge without submitting to an Imam's authority. Al-Ghazali's answer is a set of five rules of logical measurement — the Great, Middle, and Small Rules of Equivalence, the Rule of Concomitance, and the Rule of Opposition — which he derives point by point from Qur'anic verses on weighing and justice, then applies against the Mu'tazilah, the Mujassimah, and finally against the Ta'limiyyah themselves.
Brewster's introduction places the work within al-Ghazali's biography and the wider Sunni-Isma'ili conflict of the Seljuk period, and four appendices extend its usefulness: a nomenclature of the Isma'ili movement, an account of Hasan-i Sabbah's teaching drawn from Marshall Hodgson, a study of al-Ghazali's use of the syllogism with reference to Aristotle and Bernard Lonergan, and a bibliography of English translations of al-Ghazali's works. Brewster recommends reading the volume alongside al-Ghazali's autobiography, Al-Munqidh min al-Dalal, which refers to The Just Balance five times.
For students of Islamic theology, logic, and the history of the Sunni-Isma'ili polemic, this remains a compact and unusually direct entry point into al-Ghazali's method: a working demonstration, rather than a description, of how a classical Muslim theologian tested an argument.