Stephen Krashen's Monitor Model plays an important role in second language acquisition. It was evolved in the late 1970s with the influence of the Noam Chomsky's first language acquisition theory. The model comprises five hypotheses including the acquisition-learning hypothesis, the monitor hypothesis, the natural order hypothesis, the input hypothesis and the affective filter hypothesis. Krashen claims that the theory is supported by a large number of scientisfic studies. However, there are a number of limitaions in his theory. In this essay, the limitations of one of the hypothesis: the input hypothesis will be dicussed.
The input hypothesis postulates that humans acquire language in only one way- by understanding messages, or by receiving 'comprehensible input"....We move from i, our current level, to i+1, the next level along the natural order (Krashen 1985,2). Krashen regards it as an important concept in second language acquisition since it answers the critical question of how we acquire language. However, what Krashen does is not provide evidence in any real sense of the term, but simply argue that certain phenomena can be viewed from the perspective of his theory (Mclaughlin 1987, 36).
There are no clear definitions of 'comprehensible input' and 'i+1 level'. Krashen attempts to use the fact that the longer people live in a country, the more proficient their language is to prove people acquire language by receiving comprehensive input. Nevertheless, not all input is comprehensible, and the question left open is when input is comprehensible and when it is not. Krashen tries to explain the input at the i+1 level is effective in second language acquisition. This presumes that it is possible to define a set of levels and determine which structures constitute the i+1 level. However, both of them are impossible for researchers at the present stage of second language study. Krashen gives another example that hearing children of deaf parents with little exposure to comprehensible input delay in language acquisition and finally catch it up when they are exposed to comprehensible input. This evidence is again not convincing since it is not testable and there is no way of understanding what comprehensible input is.
The point that people only acquire language by receiving comprehensible input is questionable. Krashen claims that speaking is unnecessary for acquiring a second language. In his view, the only role that the speakers' output plays is to provide a further source of comprehensible input. Wong Fillmore (1976) argued that formulaic speech can help children acquire a structure consisting of a pattern or rules without having to understand the speech. Some researchers have pointed out that output is necessary since it is the way for teachers to judge the ability and progress of learners. According to Boulouffe, learners can get into the depths of modality by expressing their own feelings and thoughts. Long and Porter (1985) have proved that group conversation can increase learners' communicative ability and motivation. It is questionable whether comprehensible input alone can account for how learners correct and adjust their hypotheses about the language. Unless learners try out the language, they are unlikely to get feedback to improve.
The evidences used by Krashen seem to ignore the possibility of other explanations rather than comprehensible input in the theory. One of the arguments made for the input hypothesis is based on age differences. Krashen explains that older acquirers progress more quickly than younger acquirers in the early stages because they obtain more comprehensible input. However, it contradicts one of the main claims of the input hypothesis: simpler codes provide ideal input for i+1. If it is the case, younger acquirers should have greater advantages since they receive more repetitions and less complex grammar structures. There are other factors to explain the superiority of older learners such as their need to discuss more complex topics and the availability of mnemonic devices (Mclaughlin 1987, 39). Krashen argues that some children who come to a new country where they are exposed to a new language are silent for a long period of time since they need time to build up their language ability by receiving comprehensible input. Once competence has been built up, speech emerges. Actually, there are other possible explanations for the silent period. The children may be hesitant to speak because of anxiety and personality differences.
To conclude, the input hypothesis of the Krashen's monitor model is not substantiated by empirical studies. There is no way of determining what comprehensible input and i+1 level are and hence no way of testing the hypothesis. The importance of output is de-emphasized, and understanding a new language is given much more stress than speaking it. The argumentations are not complete enough. Other factors which are possible to account for the phenomenon are nearly neglected. The theory should be reviewed in a more balanced view critically.
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