This study develops a new approach to agreement variation in Standard Arabic (SA) and Rural Jordanian Arabic (RJA) based on the Probe-Goal framework of Chomsky (2000, 2001). The key patterns investigated are the variation in fullness of agreement in the SV and VS word orders, the relationship between agreement and clitic doubling, and the patterning of agreement with conjoined subjects. The thesis argues for a connection between agreement, clitic doubling, and word order. Full agreement on T (in person, number, and gender) causes the subject to move to [Spec, TP], deriving SV order. However, partial agreement on T (lacking person) creates only a partial copy of the subject in [Spec, TP]. This partial copy is realized as a pronominal clitic in some contexts (giving CLsVS word order) and as null pro in other contexts (giving VS word order). This approach enables a unified account of various differences in the patterning of agreement in SA and RJA. Turning to the more complex case of agreement with conjoined subjects, both varieties exhibit full resolved agreement with preverbal conjoined subjects. With postverbal conjoined subjects, however, there is variation: SA allows only partial agreement with the first conjunct while RJA allows partial agreement either with the first conjunct or with the entire conjoined phrase, depending on the features and the order of the conjoined nominals. The Probe-Goal framework augmented with Multiple Agree and the Continuity condition (Nevins 2007, 2011) will be employed to account for the choice between these two options in RJA. The more general theoretical conclusion is that the variation in agreement patterns is constrained by the internal hierarchical structure of φ-features on the probe. I propose that the probe has the same hierarchical structure as a pronoun (i.e. a DP). This proposal makes predictions about the range of possible variation in the features that are active in agreement and connects to broader issues such as the Pronominal Argument Hypothesis (Jelinek 1984) and the diachronic relationship between pronouns and agreement markers. / May 2017