Mahin Sadat Tabatabaee - Department of English Language, Malayer Branch, Islamic Azad University, Malayer, Iran
Keivan Mahmoodi - Department of English Language, Malayer Branch, Islamic Azad University, Malayer, Iran
Abbas Bayati - Department of English Language, Malayer Branch, Islamic Azad University, Malayer, Iran

Processability Theory (PT) is regarded as one of the prominent theory of second language acquisition (SLA) developed to illuminate the developmental sequences in SLA as well as some other linguistic phenomena (Pienemann, ۱۹۹۸a; ۲۰۱۱).Since ۱۹۹۰s, Processability has been at the center of attention in second language acquisition research. Within the framework of Processability theory and through analyzing the written performance of Iranian EFL learners, the present research focused on the acquisition of “Copula inversion” and “Negation” across five proficiency levels, from elementary to advanced and compared it with the stage-like development model of morpho-syntactic structures proposed by Pienemann (۱۹۹۸a, ۲۰۱۱). The study followed a descriptive method of research and the data was collected from ۳۵۰ participants in five different proficiency levels from elementary, pre-intermediate, intermediate, upper-intermediate and advanced. The participants were asked to provide samples of their written performance on different tasks such as introduction task, habitual action task, story retelling task, audio-video-retelling task, picture description task, composition, communication task. The data in this research was analyzed both qualitatively, in order to identify and classify the type and order of the morpho-syntactic structures; and quantitatively, by calculating means. The results of Kruskal-Wallis test revealed that “Negation” emerged at the elementary level of the language learners’ performance and “copula inversion” emerged at the intermediate level. Just the same, the competence of the learner grows stronger in concern with these variables through the higher proficiency levels. These findings imply that PT is valid for Iranian EFL learners, as well.   

Copula inversion, Negation, processability theory, stage-like development