This work is a comprehensive study of two well-known phonological changes in Arabic: the assimilation and the substitution. The assimilation involves the incorporation of a certain segment into an adjacent one in such a manner that they both form a doubled segment. The segments can either be identical or different. This phenomenon occurs usually in the doubled verbs and their forms and in some cases of perfects of Form V, VI and VIII. It also occurs in some other more unusual cases as in two words following each other. The substitution involves the replacement of a segment for another different one. It occurs if there is in the word a combination of two segments which is deemed as heavy, or if both these segments' points of articulation are close to each other or if they are akin in character. Other more unusual reasons relate to the peculiarity of a dialectal variant, to a verse's metrical exigency or to the exigency of the pause. This book explores in detail many various cases in which these changes are possible, necessary or forbidden. The phonological elements, the theoretical discussions and the coverage of the different works from the 8th century until our days, offer a thorough and accessible study for both the students and researchers of Arabic. About the Author Joyce Akesson has studied the Semitic languages at Lund's University, Sweden, and has previously been a lecturer there during many years. Beside the present book, she is the author of "The Essentials of the Class of the Strong Verb in Arabic" (Pallas Athena 2010), "The Complexity of the Irregular Verbal Nominal Forms & the Phonological Changes in Arabic" (Pallas Athena Distribution 2009), "Arabic Morphology and Phonology: Based on the Marah Al-Arwah by Ahmad B. Ali B. Masud" (Studies in Semitic Languages and Linguistics), Brill Academic Publishers (July 2001) and "Ahmad B. 'Ali B. Mas'Ud on Arabic Morphology Marah Al-Arwah: Part 1: The Strong Verb" (Studia Orientalia Ludensia, Vol 4), Brill Academic Pub (October 1990). She has also published several articles about Arabic linguistics in two Journals, the Journal of Arabic Linguistics (the ZAL or Zeitschrift f r Arabische Linguistik) Wiesbaden, and the previous Acta Orientalia, Denmark. She has also written a lemma about sarf "morphology/phonology in the Encyclopaedia of Arabic Language and Linguistics, vol. 4. Leiden: Brill, 2009.