The goal of the present study was to realize whether L1 (first language) or L2 (second language) affects the third language (L3) learning. Three mirror-image groups learning English were compared, as early learners of sequential Persian-Arabic bilinguals. The first group used L1 Persian-L2 Arabic languages. The second and the third groups used L1 Arabic-L2 Persian languages. Moreover, the first and the second groups used Persian, and the third group used Arabic as a language of communication. The Oxford Quick Placement Test (OQPT) was administered to select initial L3 English learners. Sixty English learners participated in the study. The translation task and Grammaticality Judgment Test were administered to elicit English attributive adjectives. To compare the performances of the three groups, the non-parametric equivalent of One-Way ANOVA, which was the Kruskal-Wallis test, was used. Mann-Whitney U tests were applied to recognize the probably significant differences among groups. None of the Cumulative Enhancement Model (CEM), the L1 Factor Hypotheses, the L2 Status Factor, and the Typological Primacy Model was confirmed. However, the influence of the dominant language of communication on L3 learning supported data. Groups one and two had better performances in the comprehension and production of attributive adjectives. Group three obtained the lowest mean score. This study lets us determine the influence of earlier acquired languages, Persian and Arabic, on the initial stage of learning L3 English attributive adjectives. The results indicate that the language of communication has a substantial effect on transferring from the first and second languages into the L3 language.
