The term “phonotactics” refers to the study of sound distribution patterns and distribution restrictions within words (and sometimes across word boundaries). Phonotactic rules influence Arabic word structure in derivational and inflectional morphology, and also in lexical root structure. Most of these rules and restrictions were discovered and described by the Arabic grammarians over a thousand years ago (in particular by Al-Khalil ibn Ahmad, but also Sibawayhi and others). They are organized and described in this book in technical linguistic terms as they apply to MSA, using formalizations whenever possible. There are at least two aspects to Arabic phonotactics: the phonotactics of root morphology and the phonotactics of derivational and inflectional morphology. The study of morphological processes interfacing with phonological structures and rules is termed morphophonemics. In Arabic the study of phonotactics and morphophonology are closely interrelated. Four phonological processes are essential to the Arabic sound system: assimilation (one sound absorbing or affecting another), epenthesis (vowel insertion), deletion (of vowel or semivowel), and vowel shift.

Assimilation (iddighaam/idghaam)

Assimilation can be defined as a change or spread of phonetic feature values (such as voicing or velarization) that makes segments more similar, or even identical. In Arabic it often occurs as a result of phonological rules applying at the intersection of morphological processes, for example, as a result of a pattern (wazn) applying to a particular lexical root (jidhr). Assimilation is normally non-phonemic; i.e., it does not affect the meaning of a segment or word. It may be progressive or regressive.