Arabic morphology is of continuing importance to students of Arabic. The Marāḥ al-Arwāḥ was written by the Baghdadi grammarian Aḥmad b. ‘Alī b. Mas‘ūd of the 8th century A.H., and is one of the very few books in this field that is published relating to this period. The work focuses on the strong verb, the infinitive noun and on their nine subordinates: the perfect, the imperfect, the imperative, the prohibition, the active participle, the passive participle and the nouns of time, place and instrument. It consists of four main parts, the Arabic edition, the translation, the commentary and the introduction. The writer does not only analyze the morphological structure of the word, but he also explains the reasons contributing to the determined measure, and he conforms them to the general principles that were already established in the Arabic inheritance. The study that emerges is an interesting integration of rationality into morphology. It also gives an insight into many of the thoughts of well-known Arabic and European grammarians.