Sunday, July 20, 2008

Krashen's Input Hypothesis

The ongoing influence of Krashen’s Input Hypothesis

There are at least forty “theories” of second language acquisition (Larsen-Freeman and Long, 1991). Of these theories, many look only at specific aspects of SLA and have followed on from research rather than preceded it. This research itself, arguably due to the complex and non-linear nature of SLA (Larsen-Freeman, 1997), is often inconclusive (Ellis, 1994). It is against this background that Krashen’s Input Hypothesis remains a seminal and influential theory of SLA. His theory is comprehensive, easily understood, incorporates suggestions for SL teachers, and has played “a crucial role in that it has led to research to validate or invalidate his claims” (USQ LIN8001 Study Book, 2008, p.33). This essay will firstly outline Krashen’s five interconnected hypotheses that make up the Input Hypothesis, and then critically discuss his claims and evaluate their usefulness with regard to SL teaching practice.

Outline of Krashen’s Input Hypothesis

Krashen (1985, p.6) summarises his own theory as implying that “language acquisition, first or second, occurs only when comprehension of real messages occurs, and when the acquirer is not “on the defensive”…”. Contained within the theory are five hypotheses on which Krashen elaborates.

1. The Acquisition – Learning Hypothesis
Krashen (1982) assumes that knowledge of a second language (SL) is developed in “two distinct and independent ways” (1982, p.10). ‘Acquisition’ facilitates fluency and is a “subconscious process” (1982, p.10), whereby the learner ‘picks up’ the language in a natural, informal and implicit way. As in FLA, error correction has little or no effect. ‘Learning’ is a conscious process, with learners being aware of the rules and formal knowledge of a language. This ‘explicit learning’ is said to be capable of being used only for ‘monitoring’ and does not contribute to language fluency. Krashen (1982) does not consider that there is an interface between these two ways of developing SL knowledge, as “language cannot ‘become’ acquisition” (Brown, 2000, p.278).

2. The Monitor Hypothesis
Strongly related to the first hypothesis, the Monitor Hypothesis explains how acquired and learned language are used in speech production. Acquired knowledge ‘initiates’ utterances and is responsible for fluency, while learned knowledge only functions as a “Monitor, or editor” (Krashen, 1982, p.15) that checks the output of the acquired language, making alterations or corrections to its form. Necessary but not sufficient conditions for the effective use of the Monitor are a concern for correctness, knowledge of the rules, and sufficient time to employ this knowledge.

3. The Natural Order Hypothesis
Based on the findings of Dulay and Burt (1974, 1975), Krashen (1982) claims that language rules and grammatical structures are acquired in a predictable, natural, and necessary order, which underlines the previous claim of acquisition being more central to SL learning, since a ‘natural order’ is “a result of the acquired system” (Gass and Selinker, 2001, p.199) and independent of instruction.

4. The Input Hypothesis
The assumption that SL acquisition proceeds in a ‘natural order’ through informal, implicit learning, means that language input, rather than language use, assumes centrality. Providing learners with input “a bit beyond (their) current level of competence (i+1)” that can be understood “with the help of context or extra-linguistic knowledge” enables them to acquire the underlying structures (Krashen, 1982, p.21). Krashen recommends that speaking not be taught directly as it will “‘emerge’ once the acquirer has built up enough comprehensible input” (Brown, 2000, p.278).

5. The Affective Filter Hypothesis
It is not sufficient for learners simply to receive comprehensible input, they also have to ‘let in’ the input for SLA to occur. Krashen (1985) claims that affective factors such as motivation, attitude, self-confidence and anxiety will affect not only the amount of comprehensible input that learners seek, but will also determine the strength of the filter, thus determining the amount of ‘comprehensible input’ reaching the LAD. Weakening of the affective filter (e.g. by strengthening self-belief, or decreasing anxiety) is therefore vital for SLA.
Krashen’s overall view of SLA
According to Krashen, learning an L2 is very much like learning an L1. No conscious effort needs to be made to focus on the language as such, since “(w)hen the filter is ‘down’ and appropriate comprehensible input is presented (and comprehended) acquisition is inevitable” (Krashen, 1985, p. 4). Therefore, Krashen not only posits the existence of a Chomskyean LAD that is available for SLA, but also denies the existence of any Critical Period after which access to UG is restricted. Instead, the reason adults may be less successful than children in acquiring a second language is that their “affective filter” is higher and they more typically use (and may erroneously be encouraged to use) their abstract problem solving skills to consciously process the grammar of an SL.

Critical discussion of Krashen’s model and evaluation of its usefulness in SL teaching

I. The Acquisition – Learning Hypothesis
Krashen’s belief that comprehensible input will lead to acquisition is based on his belief that “adults can access the same ‘language acquisition device’ that children use” (1982, p.10). The extent to which adult learners can access UG is widely disputed (see Singleton and Ryan, 1994, p.191 for a review of competing viewpoints). The evidence appears contradictory: on the one hand there is Schmidt’s (1983, cited in Schumann, 1986, p.385) case study of Wes, an adult Japanese migrant to Hawaii, who received sufficient input in a ‘natural’ setting with extensive native speaker interaction, that “did not make him a grammatically proficient speaker of English”. Similarly, in my personal experience, I have had learners in my Japanese language class, who having spent years in Japan without formal study, communicate with a wide vocabulary but in an ungrammatical fashion. On the other hand, “many people learn foreign languages without going to classes and without begin presented with the formal rules” (Mason, L5). I have also met a few such people who have successfully acquired a language as an adult; interestingly, they have all grown up bilingual or trilingual, leading me to speculate as to whether this gives them some metalinguistic knowledge or awareness that enables them more easily “to generate their own rules” (Mason, L.5, and c.f. Schmidt’s, 1993, ‘noticing’ hypothesis).

Mason’s (L.6) point that Krashen’s acquisition-learning distinction is based mainly on the observation of people learning an L2 in use in the surrounding environment and that “in other situations one may expect classroom learning, of the conscious kind, to be important”, appears valid. Brown (1990, p.280) concludes that “Krashen’s ‘zero option’ (don’t ever teach grammar)… is not supported in the literature”. If learners are adults and learning an L2 in a non-L2 environment, some conscious learning combined with plenty of practice will arguably be of more value to them than it will for a child in an immersion environment. This fits with research in cognitive science and psychology that suggests that an interface between acquisition and learning exists as a process of restructuring or assimilation, whereby new information is incorporated into existing knowledge (see Mason, L.5). It is not sufficient for learners to accumulate input passively; instead the learner will need to “actively engage with the activity”, trying out hypotheses and receiving feedback (Gagné, cited in Mason, L.5).

While rejecting an interface between acquisition and learning, Krashen (1985) accepts that learning can contribute to SLA through the mechanisms of it increasing comprehensible input to the learner, either through the learner producing their own comprehensible input which is then acquired through the LAD; through the knowledge of the rules increasing learners’ access to comprehensible input; or in so far as language study meets students’ expectations, lowering learners “affective filter” again increasing their access to comprehensible input. These mechanisms, roundabout as they are, serve to reduce some of the ramifications of a too sharp distinction between ‘acquisition’ and ‘learning’, but they shed no light on how to discern whether a learner’s output is the result of a conscious or unconscious process, nor indeed how to differentiate “what is conscious from what is unconscious” (McLaughlin cited in Brown, 2000, p.279), meaning that the hypothesis cannot be tested for falsifiability. However, despite these criticisms, SL teachers can often appreciate that at a simple level, the hypothesis reminds us that simply teaching students about the rules of a language will never produce competent users of the language, as can be typically witnessed when students, who have undergone years of L2 instruction that is predominantly explanation and translation via the L1, are unable to engage in even simple conversations. Instead, the teacher should maximise the use of the L2 in the classroom and engage learners in activities that focus mainly on meaning rather than simply on form.

II. Monitor Hypothesis
This hypothesis builds on the acquisition-learning distinction, allocating different functions to the separate systems. It has attracted similar criticism in that “it is frequently difficult to tell whether a person is monitoring using a ‘feel’ for the language (i.e. using the acquired system) or using the learned system (d’Anglejean, 1981; Rivers, 1980) thus making the hypothesis untestable” (USQ LIN8001 Study Book, 2008).

Krashen used the concept of the Monitor to explain individual differences in learners. While “optimal Monitor users can therefore use their learned competence as a supplement to their acquired competence” without interference in communication (Krashen, 1982, p.20), the speech of ‘over-users’ is halting and non-fluent since they are overly concerned with accuracy, while that of ‘under-users’ will concentrate on speed and fluency without concern for errors. These claims also have intuitive appeal to teachers, as it is usually quite easy to recognise which students, because of personality, culture, or cognitive style, have a tendency to over-use or under-use monitoring, and need to be encouraged to adjust their behaviour accordingly (e.g. through the area of focus of feedback). The optimal use of the Monitor will also depend on the situation, for example, in everyday conversations, time pressures do not usually allow for the use of the Monitor, so teachers need to discourage students from being overly concerned with accuracy in conversation (e.g. by responding to the message and not correcting students’ grammatical errors in the course of a speaking activity), whereas in formal writing, the greater emphasis on accuracy means that Monitor use needs to be encouraged.

III. Natural Order hypothesis
This hypothesis has been criticised for being based almost exclusively on cross-sectional morpheme studies (longitudinal studies have not always found a similar progression, Rosansky, 1976, cited in USQ LIN8001 Study Book, 2008) that lack linguistic relationship between items and which reflect accuracy of production rather than acquisition sequences (Mason, L.6). Mason concludes that there is a stronger case to be made for the existence of 'developmental sequences' i.e. “the learner makes certain predictable mistakes at each stage in the learning process, and that these mistakes follow a similar order whatever the mother tongue of the learner” (L.6). However, “other studies have shown that the language backgrounds of learners may also affect the order” (USQ LIN8001 Study Book, 2008, p.39).

Krashen uses the Natural Order hypothesis to support his arguments for providing only comprehensible input and not grammar instruction. In contrast, other commentators (e.g. Ellis, 1994; Gass and Selinker, 2001) note that formal, targeted learning can help learners to progress more rapidly through the stages. However, in keeping with Mason’s agreement with Krashen that “imposing the linguists' grammar on the learner - whether or not he needs it - does not have any appreciable effect on L2 acquisition” (L.6), it is useful for teachers to be aware of how textbooks may violate the order of acquisition (e.g. ESL textbooks tend to put the 3rd person present tense -s in the first part of an Elementary book whereas acquisition order studies reveal that 3rd person present tense –s is acquired at around the same time as the irregular past tense), and thus of the inappropriateness of spending too much time correcting such errors or waiting for the learner to ‘get it’ before moving on.

IV The Input Hypothesis
The term ‘comprehensible input’ means that input which is too simple (already acquired) or too complex (i+ 2/3/4…) will not be useful for SLA. While criticism has been made that the actual determining of level i and i+1 defies precision (Mason, L9), Krashen would not see this as particularly concerning in that “a deliberate attempt to provide i+1 is not necessary…it may even be harmful” (1982, p.22).

More controversial is Krashen’s claim that ‘input’ is not just more important than production, but is all that is necessary for acquisition. Krashen seeks support for his claim in FLA in children (caretaker language; delayed production) but the applicability to adult classroom learners is questionable. Mason (L.9) and Brown (2000) emphasise that ‘input’ is not sufficient because ‘output’ is a vital phase in language acquisition, with the active role of learners and their production being significant aspects of learner success (see Swain and Lapkin’s 1995 Output Hypothesis, cited in Brown, 2000). In summary of Mason (L. 9) points out that output enables the teacher to judge the learner’s progress, and choose and adapt learning materials appropriately; that producing language compels the student to “reorganise and elaborate upon his knowledge of the L2” and, through feedback, to test their hypotheses about the language system; and that input and output necessarily interact in negotiating meaning and extending learner’s linguistic knowledge. Output, and its link back to authentic input, can also give students a feeling of success from having engaged in genuine communication. For example, after suitable preparation, I send Japanese study tour students out on campus to do a simple survey on a topic of interest to them; although they are often nervous, they most often come back not only with a feeling of accomplishment from having engaged in meaningful communication, but also with new words and expressions to use.

Notwithstanding the value of output, it is also important to realise that students’ ability to produce output often lags behind their ability to comprehend input so for beginning students in particular, approaches such as TPR whereby students can respond in actions, gestures, drawing, can reduce the level of anxiety that the pressure to perform verbally may create.

V The Affective Filter
The concept of the ‘Affective Filter’ has been criticised for not delineating or explaining either the scope (e.g. variety and forms of motivation, self-confidence and anxiety – see Mason, L.11) or the process of what and how input is filtered out (Gass and Selinker, 2001). Krashen appears to use the affective filter as the default explanation of why SLA does not occur; for example he states there is a “strengthening of the affective filter around puberty” (1982, p.44) as the reason that children acquire languages more easily than adults whereas the reason may have more to do with changes in cognitive processes. McLaughlin (1987, p.56) concludes that Krashen has “provided no coherent explanation for the development of the affective filter and no basis for relating the affective filter to individual differences in language learning”.

On the other hand, the metaphor of the affective filter has been extremely influential in SLA, particular in its intuitive appeal to SL teachers to whom “experience suggests that high anxiety and low motivation do not produce good SL learning results” (USQ LIN8001 Study Book, 2008, p.43). An awareness and consideration of affective factors affecting the classroom dynamic in general and individual students in particular is essential for all teachers, notwithstanding that their complexity, interconnectedness, and differential effects are greater than Krashen suggests (see for example the discussion of motivation in Q.4). Krashen’s evaluation of testing with reference to the effect it has on the classroom also makes sense to teachers whose efforts to introduce communicative activities are often frustrated in countries where assessment is weighted towards grammar and arcane language knowledge. “Tests have a huge impact on classroom behavior, and need to be selected to encourage students to engage in activities that will help them acquire more language” (1982, p.177).


Krashen deserves credit for attempting to offer a comprehensive theory of SLA that has in turn generated wide-ranging discussion and research. However, as Larsen-Freeman and Long (1991, p.225) point out, Krashen’s theory relies on constructs (i +1 and the Affective Filter) that are “untestable, and so unfalsifiable”. McLaughlin (1987) agrees saying that Krashen merely demonstrates how “certain phenomena can be viewed from the perspective of his theory” (p. 36). Krashen also seems to believe that SLA can occur in the same way for all learners regardless of age, background or context of learning, leading to many of his hypotheses seeming under-defined and overgeneralised.

Yet despite the theoretically shaky ground, even MacLaughlin (1987, p.57) is moved to comment that Krashen may not be wrong in his prescriptions about language teaching, since many researchers “agree with him on basic assumptions, such as the need to move from grammar-based to communicatively orientated language instruction, the role of affective factors in language learning, and the importance of acquisitional sequences in second language development”. In responding to Krashen’s theory, it is arguably most useful to play both “the believing game and the doubting game” (Brown, 2000, p.290), so that most importantly, a dialogue about these influential ideas remains in place.

Reference List

Brown, H. D. (2000). Principles of language learning and teaching (4th ed.). White Plains,
NY: Addison, Wesley, Longman, Inc.

Ellis, R. (1994). The study of second language acquisition. Oxford: Oxford University

Gass, S.M., & Selinker, L. (2001). Second language acquisition: An introductory course (2nd ed.). Mahwah, New Jersey: Lawrence Erlbaum Associates.

Krashen, S. (1982). Principles and practice in second language learning and acquisition.
Oxford: Pergamon.

Krashen, S. (1985). The input hypothesis: Issues and implications. California: Laredo
Publishing Co Inc.

Larsen-Freeman, D. (1997). Chaos/complexity science and second language acquisition.
Applied Linguistics, 18(2), 141–165.

Larsen-Freeman, D., & Long, M. H. (1991). An introduction to second language acquisition
research. New York: Longman.

Mason, T. (n.d.). Lectures in SLA and EFL: Second language acquisition theory. Retrieved June 14, 2008 from

McLaughlin, B. (1987). Theories of second language acquisition. London: Edward Arnold.

Schmidt, R. (1993). Awareness and second language acquisition. Annual Review of Applied Linguistics, 13, 206–226.

Schumann, J. H. (1986). Research on the acculturation model for second language
acquisition. Journal of Multilingual and Multicultural Development, 7(5), 379–392.

Singleton, D., & Ryan, L. (2004). Language acquisition: The age factor (2nd ed.). Clevedon, GBR: Multilingual Matters Ltd. Retrieved on June 10, 2008 from

University of Southern Queensland. (2008). LIN8001 Principles of second language learning study book. Toowoomba: USQ.


hamaoui said...

it sumurizes ver Krashen's Input Hypothesis

Anonymous said...

Great work, thank you!

annalee alexander said...

thank u .... so helpful

Robert Stewart said...

Enjoyed reading this.

Anonymous said...

Thanks very much for taking the time to do this!

Chhabi Acharya said...

Good. Thank you very much!