Stephen Krashen's Theory of Second Language Acquisition
Assimilação Natural -- o Construtivismo no Ensino de Línguas
Ricardo Schütz 

"Language acquisition does not require extensive use of conscious grammatical rules, and does not require tedious drill." Stephen Krashen

"Acquisition requires meaningful interaction in the target language - natural communication - in which speakers are concerned not with the form of their utterances but with the messages they are conveying and understanding." Stephen Krashen

"The best methods are therefore those that supply 'comprehensible input' in low anxiety situations, containing messages that students really want to hear. These methods do not force early production in the second language, but allow students to produce when they are 'ready', recognizing that improvement comes from supplying communicative and comprehensible input, and not from forcing and correcting production." Stephen Krashen

"In the real world, conversations with sympathetic native speakers who are willing to help the acquirer understand are very helpful." Stephen Krashen


Stephen Krashen (University of Southern California) is an expert in the field of linguistics, specializing in theories of language acquisition and development. Much of his recent research has involved the study of non-English and bilingual language acquisition. During the past 20 years, he has published well over 100 books and articles and has been invited to deliver over 300 lectures at universities throughout the United States and Canada.

This is a brief description of Krashen's widely known and well accepted theory of second language acquisition, which has had a large impact in all areas of second language research and teaching since the 1980s.

Description of Krashen's Theory of Second Language Acquisition

Krashen's theory of second language acquisition consists of five main hypotheses:

The Acquisition-Learning distinction is the most fundamental of all the hypotheses in Krashen's theory and the most widely known among linguists and language practitioners.

According to Krashen there are two independent systems of second language performance: 'the acquired system' and 'the learned system'. The 'acquired system' or 'acquisition' is the product of a subconscious process very similar to the process children undergo when they acquire their first language. It requires meaningful interaction in the target language - natural communication - in which speakers are concentrated not in the form of their utterances, but in the communicative act.

The 'learned system' or 'learning' is the product of formal instruction and it comprises a conscious process which results in conscious knowledge 'about' the language, for example knowledge of grammar rules. According to Krashen 'learning' is less important than 'acquisition'. (Veja o texto ao lado e também outra página em português sobre Acquisition/Learning).

The Monitor hypothesis explains the relationship between acquisition and learning and defines the influence of the latter on the former. The monitoring function is the practical result of the learned grammar. According to Krashen, the acquisition system is the utterance initiator, while the learning system performs the role of the 'monitor' or the 'editor'. The 'monitor' acts in a planning, editing and correcting function when three specific conditions are met: that is, the second language learner has sufficient time at his/her disposal, he/she focuses on form or thinks about correctness, and he/she knows the rule.

It appears that the role of conscious learning is somewhat limited in second language performance. According to Krashen, the role of the monitor is - or should be - minor, being used only to correct deviations from 'normal' speech and to give speech a more 'polished' appearance.

Krashen also suggests that there is individual variation among language learners with regard to 'monitor' use. He distinguishes those learners that use the 'monitor' all the time (over-users); those learners who have not learned or who prefer not to use their conscious knowledge (under-users); and those learners that use the 'monitor' appropriately (optimal users). An evaluation of the person's psychological profile can help to determine to what group they belong. Usually extroverts are under-users, while introverts and perfectionists are over-users. Lack of self-confidence is frequently related to the over-use of the 'monitor'.



A hipótese acquisition-learning e a hipótese monitor representam a essência da teoria de Krashen.

De acordo com sua teoria, acquisition é responsável pelo entendimento e pela capacidade de comunicação criativa: habilidades desenvolvidas subconscientemente. Isto ocorre através da familiarização com com a característica fonética da língua, sua estruturação de frases, seu vocabulário, tudo decorrente de situações reais, bem como pela assimilação das diferenças culturais e adaptação à nova cultura.

Learning depende de esforço intelectual e procura produzir conhecimento consciente a respeito da estrutura da língua e de suas irregularidades, e preconiza a memorização de vocabulário fora de situações reais. Este conhecimento atua na função de monitoramento da fala. Entretanto, o efeito deste monitoramento sobre a performance da pessoa, depende muito de cada um.

Veja aqui mais sobre os conceitos de acquisition e learning.

A hipótese monitor explica a relação entre acquisition e learning ao definir a influência deste último sobre o primeiro. Os esforços espontâneos e criativos de comunicação, decorrentes de nossa capacidade natural de assimilar línguas quando em contato com elas, são policiados e disciplinados pelo conhecimento consciente das regras gramaticais da língua e de suas exceções.

Os efeitos deste monitoramento sobre pessoas com diferentes características de personalidade serão vários. Pessoas que tendem à introversão, à falta de autoconfiança, ou ao perfeccionismo, pouco se beneficiarão de um conhecimento da estrutura da língua e de suas irregularidades. Pelo contrário, no caso de línguas com alto grau de irregularidade (como o inglês), poderão desenvolver um bloqueio que compromete a espontaneidade devido à consciência da alta probabilidade de cometerem erros.

Pessoas que tendem à extroversão, a falar muito, de forma espontânea e impensada, também pouco se beneficiarão de learning, uma vez que a função de monitoramento é quase inoperante, está submetida a uma personalidade intempestiva que se manifesta sem maior cautela. Os únicos que se beneficiam de learning, são as pessoas mais normais e equilibradas, que sabem aplicar a função de monitoramento de forma moderada. Mesmo assim, numa situação real de comunicação, o monitoramento só funcionará se ocorrerem 3 condições simultaneamente:

- Tempo suficiente: que a pessoa disponha de tempo suficiente para avaliar as alternativas com base nas regras incidentes.
- Preocupação com a forma: que a pessoa concentre atenção não apenas no ato da comunicação, no conteúdo da mensagem, mas também e principalmente na forma.
- Conhecimento da regra: que a pessoa tenha conhecimento da regra que se aplica ao caso.

The Natural Order hypothesis is based on research findings (Dulay & Burt, 1974; Fathman, 1975; Makino, 1980 cited in Krashen, 1987) which suggested that the acquisition of grammatical structures follows a 'natural order' which is predictable. For a given language, some grammatical structures tend to be acquired early while others late. This order seemed to be independent of the learners' age, L1 background, conditions of exposure, and although the agreement between individual acquirers was not always 100% in the studies, there were statistically significant similarities that reinforced the existence of a Natural Order of language acquisition. Krashen however points out that the implication of the natural order hypothesis is not that a language program syllabus should be based on the order found in the studies. In fact, he rejects grammatical sequencing when the goal is language acquisition.

The Input hypothesis is Krashen's attempt to explain how the learner acquires a second language. In other words, this hypothesis is Krashen's explanation of how second language acquisition takes place. So, the Input hypothesis is only concerned with 'acquisition', not 'learning'. According to this hypothesis, the learner improves and progresses along the 'natural order' when he/she receives second language 'input' that is one step beyond his/her current stage of linguistic competence. For example, if a learner is at a stage 'i', then acquisition takes place when he/she is exposed to 'Comprehensible Input' that belongs to level 'i + 1'. Since not all of the learners can be at the same level of linguistic competence at the same time, Krashen suggests that natural communicative input is the key to designing a syllabus, ensuring in this way that each learner will receive some 'i + 1' input that is appropriate for his/her current stage of linguistic competence.

Finally, the fifth hypothesis, the Affective Filter hypothesis, embodies Krashen's view that a number of 'affective variables' play a facilitative, but non-causal, role in second language acquisition. These variables include: motivation, self-confidence and anxiety. Krashen claims that learners with high motivation, self-confidence, a good self-image, and a low level of anxiety are better equipped for success in second language acquisition. Low motivation, low self-esteem, and debilitating anxiety can combine to 'raise' the affective filter and form a 'mental block' that prevents comprehensible input from being used for acquisition. In other words, when the filter is 'up' it impedes language acquisition. On the other hand, positive affect is necessary, but not sufficient on its own, for acquisition to take place.

Veronica Nolan

Summer Institute 2001


Krashen’s Theory of Second Language Acquisition


When I enrolled in the Summer Institute, I was aware of the different second language acquisition theories.  As my time in the courses progressed, I was continually amazed to learn about the many different theories and how they apply to classroom instruction.  I found Stephen Krashen’s Monitor model interesting and wanted to know more about it.  I chose Krashen’s theory because it is multi-faceted and very interwoven.


In this paper, I will briefly explore the different hypotheses of Krashen’s theory.  In addition, I will provide examples of my classroom philosophy and how I recognize Krashen’s theory already in place.  In the future, I am sure I will encounter many more experiences to demonstrate the different hypotheses.


Krashen’s Theory of Second Language Acquisition

Stephen Krashen has published over 100 books and articles within the past twenty years dealing with second language acquisition ( Krashen’s widely accepted second language acquisition theory contains five central hypotheses. A brief discussion of each follows.


The Five Hypotheses of Krashen’s Theory


1) Acquisition-Learning Hypothesis

According to Ellis (1986), this is the essential component to Krashen’s theory. For this hypothesis, the term “learning” relates to specifically to language and refers to the ways in which “children develop first language competence” (Krashen, 1994, p. 53).  According to Richard-Amato (1996), the acquisition aspect of this hypothesis is subconscious, while the learning portion is a conscious effort by the learner.


Language acquisition occurs subconsciously while participating in natural conversations or communications where the focus is on meaning.  The learning of a language occurs separately where grammar, vocabulary, and other rules about the target language are explicitly taught.  There is a focus on analyzing errors and correcting them.  The focus in the aspect of “learning” is not on the content or meaning of the conversation or book, but rather on the structure of the language.


2) Natural Order Hypothesis

This portion of the theory “states that students acquire (not learn) grammatical structures in a predicable order” with certain items being learned before others (Krashen, 1994, p. 52). This order seems to be independent of the learner’s age, the conditions of exposure, and the background of the L1 development (  According to Krashen (1994), natural order patterns of second language acquisition do not follow those of the first language acquisition patterns. Nonetheless, there are patterns to L2 development.


However, the L2 acquisition patterns of a child are very similar to the L2 learning patterns of an adult.  Krashen (1994) points out that “the existence of the natural order does not imply that we should teach second languages along this order, focusing on earlier acquired items first and acquired items later” (p. 53). In most of the Spanish classes offered at the middle and high school, I would say the primary mode of instruction could be based upon this hypothesis.  Except that instructors may be focusing on the “learning” as opposed to the acquisition of their students. Basic elements of the language were taught first and then gradually progressed to the more complex elements. 


This is evident in learning verb conjugations, as well as in learning the different vocabulary and semantics.


In many ways, this approach to instruction may be helpful to many students.  It provides a strong foundation in language mechanics.  However, I think it may also hinder the student in that many times they may find themselves thinking about which rule to apply when speaking and this may often negatively affect the proficiency and flow of communication. At the same time, some one could argue that this is an example of the over use of the Monitor model.  In reality, both apply to this situation.  This influences my curriculum on a daily basis.  I agree that at first a foundation needs to be laid and then the house of language can be built.  I use this to ensure that my students are not only taught in this manner, but also engage in many other language experiences in a more holistic manner.  Examples will be discussed later in this paper.


3) Monitor Hypothesis

The Monitory Hypothesis of Krashen’s theory proposes that there is a ‘monitor’ which functions to help the person to, in essence, filter his/her language.  The person uses the monitor to apply rules to the already learned knowledge, such as which verb tense to use or which form of speech to use. Krashen (1994) explains that in order to use a monitor well, three factors must be met: (1) time; (2) focus on form; and (3) knowledge of the rules.


Krashen also proposes that the use of the Monitor varies among different people.  There are those who use it all of the time and are classified as “over-users”. There are also learners who either have not learned how to use the monitor or choose to not use it and they are identified as “under-users”. The group in between these ends of the spectrum are the “optimal users”.  These people use the Monitor appropriately and not to either extreme. A psychological profile of the language user is helpful to determine in what group they belong. (


4) Input Hypothesis

I find Krashen’s input hypothesis to be very similar to that of Vygotsky’s Zone of Proximal Development.  The Input Hypothesis poses the concept represented by  i+1; where the i represents the “distance between actual language development” and  i+1 represents “the potential language development”(Richard-Amato, 1996, p. 42). The learner is unable to reach the i+1 stage without the assistance of others.  An example of assistance would be that found in a peer-tutoring situation.  For example, when I have had my students interview people, I pair them so that their language proficiency levels are different.  This provides the opportunity for students to construct comprehensible input for each other. For instance, if one of the students is struggling to express him/herself, the other student can provide the comprehensible language in a meaningful context.  I find that children consistently have a quick and natural way of conveying their meaning to their peers.  I also think that because it comes from their peers, it assists with lowering the affective filter as well.


There are three key elements to this hypothesis. First, language is acquired, not learned, by the learner receiving comprehensible input that has arrangements or structures just beyond the learner’s current level of mastery (i+1).  Next, speech should be allowed to emerge on its own. There is usually a silent period and “speech will come when the acquirer feels ready. The readiness state arrives at different times for different people”(Krashen, 1994, p.55).  It should not be taught directly and a period of grammatically incorrect speech is typical. Finally, the input should not deliberately contain grammatically programmed structures. “If input is understood, and there is enough of it, i+1 is automatically provided”(Krashen, 1994, p. 57)


5) Affective Filter Hypothesis

Dulay and Burt (1977) proposed the idea of the Affective Filter being something which determines to what degree a person learns in a formal or an informal situation (as cited in Baker, 1996).  Affect is defined as “the effect of personality motivation and other ‘affective variables’ on second language acquisition” (Krashen, 1994,p.57). Krashen applies this theory to language learning and looks at its influences on the rate of second language acquisition in three areas: anxiety, motivation, and self-confidence.


If a learner has low anxiety, high motivation, or high self-confidence, s/he is said to have a low affective filter. This in turn assists with allowing in more information and providing a fertile venue for learning.  On the contrary, if a person has high anxiety, lower motivation, or a lower self-esteem, the affective filter will be higher and does not provide the learner with as many “subconscious language acquisition” (Krashen, 1994, p. 58) opportunities as that of a person with a low affective filter.


Personal Philosophy and How It Compares To Krashen’s Theory

I taught first and second grades at an elementary school in the South Broadway area of Albuquerque, New Mexico. I taught at this elementary school for six years. I enjoy teaching in culturally diverse settings and would not trade anything for the experience that my teaching has provided me.


The population of this elementary school was predominantly Mexican and Hispanic, with the next largest population being African American. Anglo and Native American students made up the smallest percentage of the student body.  This elementary school is a Title I school and continues to receive funding for Bilingual Education services. The majority of the student body received free or reduced meals.


The most important aspect of my teaching philosophy is that my classroom is a community where everyone is a valued member. In the beginning of the year, I spend the first month establishing the classroom rules, consequences, and general procedures. The children assist in constructing the rules. I limit the rules to four items and there are four consequences.  The rules focus on respect and caring for one another and their surroundings.  There is positive recognition built into the behavior management system, as with all of my instruction.


When I was exposed to Vygotsky, I immediately agreed with his Zone of Proximal Development (ZPD) theory.  The ZPD is “the difference between the child’s capacity to solve problems on his own, and his capacity to solve them with assistance” ( Basically, this means that the child’s actual level of development indicates what the child can accomplish without assistance.  The ZPD, on the other hand, refers to the activities and functions that the learner can accomplish only with the help of another person. Learning is built upon experiences through a process often refereed to as “scaffolding” and the person who acts as a guide through the ZPD can be a teacher, parent, caretaker, or another student.


I believe that this is how all people learn because learning does not occur in a vacuum. I believe that when learning transpires, there is always an influencing factor, such as a guidebook, a teacher, a peer, or an instruction sheet present. Guidance needs to take place in order for learning to follow. If a student is presented with information that is not the slightest bit comprehensible and no assistance for understanding is provided, chances are that the student will struggle and likely give up.


In my own teaching I have witnessed students giving up because the assignment or task was not understandable to them. The topics have ranged from math to science to writing.  The reason that various students gave up was because the input was not comprehensible to them and the appropriate assistance was not offered at the crucial time of need. As Krashen (1994) mentions in his article, every person is at a different i+1 state or if I were to look at it form the Vygotskian viewpoint, everyone has a different ZPD. My personal challenge over the past years has been to focus on each student’s individual level and how to best meet his/her own ZPD needs.


The use of peer tutoring is one of my strongest teaching strategies.  Along with my philosophy of every class member being an integral part of the whole, I strongly believe that I am not the only teacher nor the only student in the classroom. The students are all skilled in a multitude of aspects and I utilize those strengths to assist their peers with learning new concepts.  Not only do I have peer tutors within the classroom, I have often paired up with different classes in the school for various activities. Thinking back to my observations of my students, I have witnessed many instances of students clarifying information for their peers. Through the clarifications, the language experience is thus enriched. This in turn provided more opportunities for acquisition of language as defined by Krashen in his Acquisition-Learning Hypothesis. With the conversations being authentic, this further enables the acquisition because the focus of the conversation is on meaning.


Another constant in my classroom was conversation. I strongly encouraged my students to discuss everything.  My philosophy is that as long is there is learning occurring, there will be discussion. As Vygotsky stated, “Thought is not merely expressed in words; it comes into existence through them” (Vygotsky, as cited in Guerra & Schutz). Through spoken modeling on my behalf, my students learn methods which help them in their peer tutoring and in their own learning.


As for the Monitor Hypothesis, I can confirm to this aspect of Krashen’s theory as being supported in my classroom as well.  Through my efforts of providing that crucial wait time after I have asked a question, I am allowing my students, L1 learners as well as L2 learners, the time to use their Monitor if they wish, to construct a response or to contribute to the discussion.  All of my students make mistakes when speaking at one point or another and I have listened to them process their own corrections or help other students correct their speech. This process helps everyone involved to learn and provides the needed ingredient for the i+1 aspect of Krashen’s theory.



I have found that in addition to second language learning in my classroom, Krashen’s theory applies in general to all learning. The students acquire knowledge in different ways than they do when they are specifically taught skills. As the learner progresses on his/her path of language acquisition, there are various stages which are like the stages of a butterfly.  All of this learned material is put to use, most of the time being processed through a filter of sorts, which Krashen calls the Monitor.  This is where the rules are applied and the form is checked. If it is not right, it is corrected to fit the rules. All of this information is useful, but without assistance and a low affective filter, the student cannot achieve the i+1 place in learning.


The study of Krashen’s theory has helped me to further understand how a person acquires a second language. This information will not only help me to be a better teacher for my L2 learners, it will make me a better teacher.






Baker, C. (1996). Foundations of bilingual education and bilingualism, second edition.  Bristol, Pennsylvania: Multilingual Matters.


Ellis, R. (1986). Theories of second language acquisition. Making it happen: Interaction  in the second language classroom. From theory to practice (pp.390-417). White Plains, New York: Longman.


Guerra, C. and R. Schutz. Vygotsky.  Retrieved June 19, 2001 from the World Wide Web:


Krashen, S.D. (1994). Bilingual education and second language acquisition theory. In bilingual Education Office (ed.) Schooling and language-minority students:  A theoretical framework (2nd ed., pp. 47-75). Los Angeles: Evaluation Dissemination and Assessment Center, California State University.


Richard-Amato, P.A. (1996). Making it happen: Interaction in the second language  classroom. From theory to practice. White Plains, New York: Longman.

Stephen Krashen’s Theory of Second Language Acquisition. Retrieved June 19, 2001  from the World Wide Web: