Error analysis has been at the centre of attention of many linguists, language teachers, and educational researchers for the reason that errors both contain useful information about the stages that language learners go through when they acquire the target language (Burt, 1975; Corder, 1967, 1981; Dulay & Burt, 1974; Richards, 1974; Taylor, 1975) and provide indirect feedback and constructive reflections on instruction and teaching practices (Corder, 1967; Ellis, 1986; Hyland & Hyland, 2006). As Corder (1967) highlights, learners’ errors are “significant in (that) they provide to the researcher evidence of how language is learned or acquired, what strategies or procedures the learner is employing in the discovery of the language” (p. 167). In a similar vein, Ellis (1997) asserts that classification of errors could facilitate the diagnosis of language learning problems at various stages of development and the discovery of the changes occurring in error patterns over time.

With the growing research interest in the analysis of errors, a range of strategies have been adopted by various researchers. As a well-known strategy, Corder’s (1974) error analysis procedures consist of selection of the corpus; identification of the errors in the corpus; and classification, explanation, and evaluation of the errors. When attributing a cause or source to each error, a variety of explanatory methods or interpretative techniques are used. According to Taylor (1975), errors might be caused by the contextual factors such as improper learning environment, teaching materials, teaching methods, faulty presentation, and teacher’s ignorance. However, common sources of linguistic errors are classified as either interlingual or intralingual transfers (Brown, 1980, 1987, 1994; Ellis, 1997; Ferris, 2009; Gass & Selinker, 2001; Selinker, 1972; Richards, 1974; Taylor, 1975). The interlingual(interlanguage) errors referring to the negative transfer of the native (first) language are defined as the halfway between a learner’s own language and the target language (Selinker, 1972); whereas the intralingual (developmental) errors represent the negative transfer of language items and rules within the target language (Richards, 1974).

Adopting a selective error analysis strategy, this study focuses on subject-verb agreement (SVA) rather than attempting to analyze all the written errors in a particular essay. The rationale behind this decision is that EFL learners at various levels of proficiency in various educational settings have difficulties in employing the rule regarding subject-verb agreement (Elkılıç, 2012; Gustilo & Mango, 2012; Sert, 2005; Surina & Kamarulzaman, 2009; Thep-Ackrapong, 2005). In this line, this study aims to analyze the written works of Turkish learners of EFL with the purpose of investigating the cases lacking subject-verb agreement. The study aims not only to detect the errors and describe the reasons for their occurrences but also to provide implications for the prevention of future occurrences. On the basis of Corder’s (1967) proposition, errors in this study serve two purposes: (a) diagnostic purpose to provide information about the acquisition process of the participant learners; and (b) prognostic purpose to help teachers to modify their materials and methods to meet the learners’ problems.

In the light of the aforementioned purposes, the study aims to address the following research questions: How frequent do the errors indicating a subject-verb disagreement occur in written works of Turkish learners of EFL?; What categories and sub-categories emerge as a result of the classification processes?; What are the frequencies and percentages of the occurrences within each category and sub-category?; Do the errors differ with respect to the proficiency level of the learners?; How can those errors be reduced and prevented?; and How can this error analysis be used as a tool in instructional planning? 

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