During second-language acquisition (SLA), it is not possible that learners start speaking the target language (TL) fluently and accurately without facing certain problems and committing countless lexical, syntactic and pronunciation errors.

Though these errors are often considered nuisance to be eradicated by many people, linguists — applied linguists that focus on language acquisition in particular — have, and are still attempting to study these errors to effectively treat them. They perceive the errors as traces of the learner’s progress in language learning and cues into how language is actually learned or acquired.

For this reason, three major approaches to the study of learner’s errors have been presented, namely contrastive analysis, error analysis and interlanguage theory. An error is defined as any systematic deviation from the imminent rules of the TL. It cannot be self-corrected since it is the result of incomplete learning and linguistic incompetency as the learner is not aware of what is presumed to be correct; therefore it reflects the gap in the competence of the learner.

Errors are generally classified into local errors, which do not hinder communication, and global ones, which do interfere with communication and disrupt the meaning of utterances. Within SLA, errors are distinguished from mistakes (also called performance errors). The latter are random deviations and unrelated to any system; they are related to performance and usually take place because of the speaker’s failure to utilize a known system correctly due to non-linguistic factors such as fatigue, strong feeling, memory limitations, lack of concentration, and the like.

The first approach to the study of these errors is Contrastive Analysis (CA). It found its theoretical foundations in Lado’s book Linguistics across Culture. At that time, language learning was considered –by behaviourists - as a set of mechanical habits which are formed through a process of imitation and repetition, and so Lado (1957), influenced by them, argued that the linguistic errors and the difficulty in mastering certain structures in a second language arise from the differences between the mother language and the TL, which lead to interference (negative transfer). For this reason, CA hypothesis claimed that a structural comparison the two languages in question would enable us to predict and describe the learning problems that are likely to be faced by learners/ students.

Although many errors are indeed interlingual errors caused by a negative transfer from the learner’s L1 to TL, CA was criticized for two main reasons: first, many predicted errors – which were supposed to be committed – were inexplicably not apparent in learner’s performance; and second, other observable errors were, in fact, irrespective of their mother language.

By contrast, the second approach — Error Analysis (EA) — provided a better explanation for the causes of such errors. EA in SLA was established in the sixties by Corder and colleagues. Instead of comparing L1 and L2 to predict errors, EA focuses on the errors that actually occur among language learners and studies them in the broader framework of their sources and significance.

EA, while affirming that one source of learner’s error is interlingual as in CA, also distinguishes a second type of errors that are deemed to be of intralingual interference. In EA, the first step in studying errors is to collect data from the learners, followed by the identification of errors that are committed when the learners misuse some TL rules (as opposed to mistakes); then describing the errors by classifying them into sub-categorizations: overgeneralizations - applying rules in cases where they do not apply - incomplete rule applications such as simplifications – omission, addition… -, and the hypothesizing of false concepts - deriving from faulty comprehension of distinctions in the TL; and stating the frequency of each error type.

After that, the area of difficulty in the TL is identified (explanation) to, finally, evaluate and correct the errors. However, this approach has also been criticized, mainly because it does not take into account the avoidance phenomena by which language learners employ the strategy of avoiding certain difficult TL elements.

Because of this, another approach — interlanguage theory — was presented. The theory is often credited to Selinker, who coined the term, and it draws attention to the possibility that the learner’s language can be regarded as an independent, self-made linguistic system incorporating numerous variations and deviances which result from his/her attempted production of a TL. The learner does this using certain strategies such as: language transfer, transfer of training, communication strategies, learning strategies including the preservation of some features of his/her first language and the overgeneralization of some TL rules… etc.

The problem with this technique, however, is that, in some cases, it can lead to what Selinker calls fossilization, i.e., the permanent cessation of progress toward the TL (the items, rules, and sub-systems that L2 learners tend to retain in their IL). In this approach, the errors made by the learners are routes that must be passed, and they are considered as proof of hypothesis testing - the learner’s testing of his hypotheses regarding the TL by uttering something and receiving feedback from an interlocutor.

When teaching a foreign language, there are many ways the teacher can respond to, and treat the errors of students in a constructive way. These include, - but are not limited to - creating an autonomous ability in learners to correct themselves given that their discovery of patterns of error is more effective. Also, in some cases, the teacher should not let the errors go uncorrected because they may lead to the persistence and perhaps the eventual fossilization of such errors; in this case, a post-lesson cognitive or affective feedback said in private are advisable to prevent the student from embracement or potential feeling of devaluing which might ensue if they are corrected – negatively - in front of their classmates.

The teacher should also focus on the most frequent, serious errors without too much attention on every small one; otherwise, the treatment is likely to be inefficient and lead to demotivation.

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