The goal of this study is to propose an Optimality-Theoretic (OT) account of the assimilation that arises from adjacency between root and pattern consonants in the two verbal patterns “ɪn-a-a-” and “ɪ-ta-a” in Modern Standard Arabic (MSA). As for the pattern of “ɪn-a-a-”, ranking syntagmatic constraints higher than the faithfulness constraint of the root explains why the nasal /n/ agrees with the first radical in place features. In the second pattern (“ɪ-ta-a-”), ranking syntagmatic constraints higher than the faithfulness constraints correctly predicts the change of the pattern affix /t/ to [d] provided that it follows a voiced coronal consonant. This ranking also successfully explains why /t/ becomes emphatic (i.e., [tˤ]) when it occurs after an emphatic radical. Some constraints are posited in order to account for the change of pattern /t/ into /w/ when the latter comes after the vowel /ɪ/.