Stephen Krashen and Second Language Acquisition

Modified: 21st Sep 2021
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Linguist Stephen Krashen was born in Chicago, Illinois in 1941. Krashen is well known for his second language acquisition theories. According to Dr. Kathy Escamilla and Elizabeth Grassi of the University of Colorado, Krashen was a close follower of the works of linguist Norm Chomsky. Krashen developed his theories based off of Chomsky’s concept of language acquisition. His theories are broken into five hypotheses that create a framework for teaching a second language: the Acquisition-Learning hypothesis, the Monitor hypothesis, the Natural Order hypothesis, the Input hypothesis, and the Affective Filter hypothesis. “These hypotheses lay the foundation for the communication-based teaching strategies that have become popular with many instructors today.” (Escamilla & Grassi, 2000, p. 2).

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Acquisition-Learning Hypothesis

Krashen believes that language acquisition and language learning are two very distinct, separate things. According to Herrell & Jordan, Krashen believes that the distinction between the two are “vital in supporting students’ gradual acquisition of fluency in a new language.” (Herrell & Jordan, 2016, p. 2). Language acquisition is an unconscious process where language in naturally acquired and when language is used meaningfully. It follows a similar pattern to the development and understand of the first language. A child born in an American home to English-speaking parents subconsciously learns the English language through language acquisition. It develops through meaningful interactions with native speakers. In a school setting, this would include a native English-speaking student and a native Spanish-speaking student (learning English as a second language) engaging in conversation on the playground during recess. Grammar rules are not a main focus in language acquisition. Language learning on the other hand, is consciously learning about a language through formal instruction. Language learning also includes learning about the rules of a language. Grammar rules, vocabulary and language functions are taught explicitly through formal language learning. (Richards & Rodgers, 2001).

Monitor Hypothesis

Krashen’s second hypothesis is the Monitor hypothesis. Krashen believes that grammar learning occurs through the use of a monitor. This hypothesis explains the relationship between acquisition and learning and defines the influence of learning over the former. In Ricardo Schutz explanation of Krashen and his theory, he states that Krashen believes that the acquisition system is the initiator and the learning system performs the role of the ‘monitor’ or the ‘editor’. (Schutz, 2005, p. 2). The input of the Monitor hypothesis is the acquired competence. There is also a learned competence, which is the monitor. The monitor requires three conditions to be met: adequate time at his/her disposal, knowledge on the rules, and a focus on the form or correctness of the grammar. The acquired competence (input) goes through the monitor to create the output. The monitor examines the output.

According to professor and author Joan Wink in her YouTube lecture on Krashen, “a monitor inhibits speech.” Wink gave a real-life example of her husband, who had recently begun learning Spanish after moving to Arizona. His monitor inhibited his speaking. “His monitor blocked his speaking because his cognitive brain was always trying to figure out what verb tense to add, instead of just saying it how he had naturally acquired it.” (Wink, 2015).

Natural Order Hypothesis.

The third hypothesis in Krashen’s theories is called the Natural Order hypothesis. Krashen believes that the acquisition of grammatical structures follow a predictable, natural order. Some of these grammatical structures are acquired earlier and others are acquired much later. If a teacher attempts to teach structures that do not fall within that natural order that students are unready for, language acquisition will not be improved. . (Schutz, 2005, p. 3).

Input Hypothesis.

In his Input hypothesis, Krashen explains how the learner acquires a second language, or how second language acquisition takes place. According the Schutz, the input hypothesis is only concerned with the ‘acquisition’ of the second language, not the ‘learning’. (Schutz, 2005, p. 3). Language acquisition occurs through interactions slightly beyond the learners present level of competence. For example, if a learner is at stage, I, the maximum acquisition takes place when they are exposed to ‘Comprehensible Input I + 1’. (Hatfield, 2013). In Krashen’s scenario with I and +1, the ‘I’ represents the child and their present stage of acquisition and the ‘1’ represents the more advance input provided for the child to progress beyond their present stage. (Escamilla & Grassi, 2000, p. 3).

 Comprehensible input is language, that is either written or heard, that is understood by the learner. According to professor Craig Hughes, comprehensible input occurs when contextual cues provide language cues. For example, when speaking with someone who is having a difficult time understanding the language, using hand gestures, changing the tone of your voice or creating illustrations as you speak may better help them understand. (Hughes, 2016). Without comprehensible input, the learner if left with a group of words perceived as an incomprehensible noise and cannot be processed in the LAD, or  Language Acquisition Device  (Escamilla & Grassi, 2000, p. 2-3).

Affective Filter Hypothesis.

The final hypothesis in Stephen Krashen’s theory of the Second Language Acquisition is the Affective Filter hypothesis. Krashen believes there are a number of affective variables that play a role in second language acquisition. Examples of these variables include motivation, self-confidence, and anxiety. The emotions of the learner can either interfere or help with their language acquisition. “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.” . (Schutz, 2005, p. 3) Negative emotions such as low motivation, anxiety, or low self-esteem create a filter that prevents comprehensible input. As previously mentioned, a lack of comprehensible input causes language acquisition to not be processed. Schutz explains it best in his statement, “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.” (Schutz, 2005, p. 3)

Krashen’s Theory and Constructivism.

As defined by the University of Sydney’s School of Education and Social Work program, constructivism is a learning theory that explains how people acquire knowledge and learn. Constructivism suggests that knowledge and meaning is constructed through one’s personal experiences. Popular contributors to the constructivism learning theory are Lev Vygotsky and Jerome Seymour Bruner.

 Lev Vygotsky is most well-known for his theory of the Zone of Proximal Development, the ZPD. There are three levels to the ZPD concept. Imagine three circles interlaid on one another. The smallest, innermost circle is the first level, which refers to what a learner can do without help independently (what is known). The middle circle or level refers to what the learner can do with guidance and encouragement from an adult (the knowable). This middle circle represents the zone of proximal development. The outermost circle represents what the learner cannot do, even with guidance (the unknowable). According to Saul McLeod, “The zone of proximal development refers to the difference between what a learn can do without help and what he or she can achieve with guidance and encouragement from a skilled partner.”  (McLeod, 2019.)

Stephen Krashen’s Input hypothesis theory closely relates to Vygotsky’s Zone of Proximal Development. Hatfield claims this is no coincidence, as Vygotsky heavily influenced Krashen’s second language acquisition theory, which is the Input hypothesis theory. (Hatfield, 2013). According to Hughes, “Language acquisition occurs through interaction just beyond present ability.” (Hughes, 2016). In relation to Vygotsky, the language acquisition would fall under the learner’s zone of proximal development, because it is presented at a level just above their independent level. With guidance and encouragement, the learner will be able to achieve in the interactions presented at this level.

Classroom Application.

In my future classroom, I believe it is important for me to take Krashen and his five hypotheses into consideration. In order to be an effective teacher for my students acquiring a second language, it’s important that I understand Krashen’s theories and find ways to implement his ideas into my classroom.

One of the most crucial hypotheses of Krashen to implement into my own classroom as an educator is the Input hypothesis. As previously mentioned, this hypothesis is closely related to Vygotsky’s zone of proximal development. In my classroom, I plan to combine Krashen and Vygotsky’s theories together. I will ensure that I am teaching to all of my students within their zone of proximal development. To do this, I plan on scaffolding my instruction. I will assess my students on their prior knowledge. Using that information, I can build my instruction off of my students knowledge to scaffold. I will help my students move from what they already know, to what is knowable or just beyond their present level of ability. I will also scaffold by differentiating my instruction to my learner’s needs. To differentiate, I will implement the use of both homogenous grouping and heterogenous grouping. Homogenous grouping will allow ease for adjusting to students learning by ability. Heterogeneous grouping is also important for my students to be exposed to new concepts and learning, as well as give students the opportunity for peer interaction, which assists with language acquisition.

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 Another way I will implement Krashen’s Input hypothesis theory is by using the teaching strategies as described by Escamilla and Grassi. According to their article, “Input becomes comprehensible when the teacher uses strategies such as: showing pictures or visuals to accompany new vocabulary words and communicative concepts, incorporating gestures, drama and music into lessons, designing lessons with hands-on activities and manipulatives, repeating vocabulary, and translation.” (Escamilla & Grassi, 2000, p. 2-3). Within my lessons, I plan on incorporating a lot of visuals or pictures to accompany any new vocabulary words I present to my students. Along with the visuals and vocabulary words, I will provide translations of the words into the native language of my second language learners. Escamilla and Grassi note that it is important for  a teacher to not rely on using transactional as a common teaching tool in the classroom, because students will focus their attention on the translation rather than the English word. I agree with their suggestion and in my classroom, I plan to use these translations as a way to assist my students in their learning for key concepts only, to ensure they are focusing most of their attention on the English version of the word or concept.

 I also plan to use hands-on activities or manipulations within my lessons, which is another strategy to helps create comprehensible input. For example, when my kindergarten students are working on writing their letters, they will have a variety of options and activities to complete the task, such as writing in sand, creating letters out of play-dough or using alphabet fridge magnets. To help my students understand the concept of force and motion within their science lessons, my students will use dominos stacked on the table in a row. With their finger, they will push one end domino down to represent force. The falling of all of the dominos is the motion.

  Krashen’s fifth hypothesis theory is the Affective Filter hypothesis. As previously mentioned, Krashen believes there are variables, such as motivation, anxiety or self-confidence, that play a role in second language acquisition. Some of these variables are not influenced by the classroom environment, although they can be. In my future classroom, I plan on giving my students a positive classroom environment where my students will feel motivated by myself and their peers and less anxious. I plan to use positive language, interact with my students in and out of the classroom and encourage my students to be supportive of one another. With this idea in mind, I hope it will provide my students with positivity that will decrease the likeliness of them creating that affective filter that blocks comprehensible input from being used for acquisition.


Stephen Krashen and his five hypotheses – the Acquisition-Learning hypothesis, the Monitor hypothesis, the Natural Order hypothesis, the Input hypothesis, and the Affective Filter hypothesis – play a significant role in second language acquisition. His ideas provide a foundation for educators and their teaching of second language learners. In order to understand how second language learners acquire language acquisition, we must understand Krashen’s theories. It is important for educators to remember that, according to Krashen, language acquisition is much more important than language learning. Educators should also remember they should attempt to present as much comprehensible input as possible in order to support language acquisition.

As a future educator, I plan to use various strategies in my classroom in order to present comprehensible input and support my second language students in the best way possible by adapting to their needs and implementing Krashen’s theories into my curriculum.



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