Monitor theory

Monitor Theory refers to five hypotheses developed by the linguist Stephen Krashen to explain second language acquisition (SLA):


 * the acquisition-learning hypothesis;
 * the monitor hypothesis;
 * the natural order hypothesis;
 * the input hypothesis;
 * the affective filter hypothesis.

The acquisition-learning distinction is the most fundamental of these and the most widely known among linguists. According to Krashen these are two independent systems of L2 performance; acquisition is a product of subconscious processing similar to children’s L1 acquisition and requires life-like L2 interaction, which focuses on communication rather than correctness, while learning occurs through formal instruction and comprises conscious processing, which results in knowledge about the L2, e.g. grammatical rules. Krashen believes ‘learned competence’ acts as a monitor or editor: that is, whereas ‘acquired competence’ is responsible for the fluent production of sentences, ‘learned competence’ consciously corrects them. He claims that learned knowledge enables learners to read and listen more, so acquisition is effective.

The monitor hypothesis asserts that a learner's learned system acts as a monitor to what they are producing. In other words, while only the acquired system is able to produce spontaneous speech (according to this theory), the learned system is used to check what is being spoken. The interlocuter therefore monitors their spontaneous speech using their learned system. The Monitor Model then predicts faster initial progress by adults than children, as adults use this ‘monitor’ when producing L2 utterances before having acquired the ability for natural performance, and adults will input more into conversations earlier than children. However, in the long term, SLA started in childhood will be superior in ultimate attainment as children will already have control of some L2 acquired before pubertal changes began inhibiting learning.

The input hypothesis states that only comprehensible input will result in acquisition of the target language. Krashen says that learners must be exposed to input that is just beyond their current level in order to make progress. This concept is called i+1. If the level of input is at i+1 the learner will make progress. If it is too high, for instance i+7, the learner will be unable to acquire it.

The affective filter hypothesis asserts that a learner's emotional states act as adjustable filters that freely permit or hinder input necessary to acquisition. He suggests that adolescence and puberty are not good periods for SLA, as this ‘affective filter’ arises out of self-conscious reluctance to reveal oneself and feelings of vulnerability.

The model has been criticised by many linguists and is no longer considered a valid hypothesis. Its continued value in the field is only for its historical significance, and the research it has inspired. McLaughlin (1987) claims that none of the hypotheses is clear in its prediction, for example, the acquisition-learning distinction is not properly defined and the distinction cannot be empirically tested. If only acquired forms can lead to spontaneous speech, as Krashen claims, then it should be impossible for anyone who learns a foreign language in a classroom, and is taught it in their native language, to ever be able to produce spontaneous speech in the target language. This is clearly untrue. Likewise, Krashen provides no criteria for establishing i+1, or for delineating different levels of input. Similarly, the monitor hypothesis and the affective filter hypothesis are not falsifiable either. For one thing, the value of a monitor that only notices mistakes after they are produced is questionable. Furthermore, there is no way of determining how the monitor works or proving if it is even there at all. If a learner produces a correct form in the target language, it is impossible to determine what caused them to produce that form. There is no way to prove whether it was their acquired system or their learned system, if there is even a distinction between the two. Similarly, there is no way to prove how the affective filter hypothesis filter works. The affective filter hypothesis also fails to take into account why a motivated learner, whose affective filter should be down, could still have trouble learning a language.

However, continued interest in Krashen’s theory indicates this theory is far from pseudo-scientific. In determining an optimal SLA age, the variables these theories propose are not the only possibilities: affective factors, including motivation and fear, also influence language-learning attitudes. These factors can explain maturational differences in SLA: older learners often learn new languages for economic or academic reasons, and therefore work harder to reach their target fluency.

The theory underlies Krashen and Terrell's comprehension-based language learning methodology known as the natural approach (1983).