Commentary on Surah al-Fatiha

Ar-Razi's commentary on Surah al-Fatiha spans several volumes and stands as one of the most exhaustive treatments of the opening chapter of the Quran in the tafsir tradition. He begins by examining the names of the surah, cataloguing the various designations scholars have given it — Umm al-Quran (Mother of the Quran), Umm al-Kitab, As-Sab' al-Mathani (The Seven Oft-Repeated), Al-Asas (The Foundation) — and explaining the theological significance of each name.

For the Basmala, ar-Razi devotes extensive discussion to the question of whether it is a verse of al-Fatiha or a standalone verse revealed before each surah. He presents the Shafi'i position that it is a verse of the surah, the Maliki position that it is not, and the Hanafi view, marshaling linguistic and hadith evidence for each. His treatment is characteristic of his methodology: he raises every conceivable objection and works through them one by one.

On the Divine Names Rahman and Rahim, ar-Razi provides a detailed semantic and theological discussion. He examines the root r-h-m and its derivatives, the difference in grammatical form between the two Names (one being a hyperbolic form, the other indicating continuity of action), and the Ash'ari position that Divine Names are eternal attributes established by revelation. He refutes the Mu'tazili interpretation that these Names are merely metaphors for Divine reward rather than descriptions of an actual divine attribute.

The verse Al-Hamdu lillah (All praise is for Allah) gives ar-Razi occasion to discuss the nature of praise (hamd), thankfulness (shukr), and glorification (tasbih), distinguishing between them philosophically. He argues that genuine praise requires cognizance of the praised one's perfections and that the Quran's opening with hamd trains the believer to orient every moment of consciousness toward the recognition of divine goodness.

Ar-Razi's discussion of Iyyaka na'budu wa iyyaka nasta'in (You alone we worship and from You alone we seek help) addresses free will and divine decree at length, presenting the Ash'ari doctrine of kasb (acquisition) as the correct middle ground between absolute human freedom and absolute determinism. This passage is among the most philosophically dense in the entire Mafatih al-Ghayb and has been the subject of commentary by later scholars across several generations.