summary by Reid Wilson

Bibliographic information:

Krashen, Stephen D. 1981. Principles and Practice in Second Language Acquisition. English Language Teaching series. London: Prentice-Hall International (UK) Ltd. 202 pages.

Quote that captures the essence of the book:

"What theory implies, quite simply, is that language acquisition, first or second, occurs when comprehension of real messages occurs, and when the acquirer is not 'on the defensive'... Language acquisition does not require extensive use of conscious grammatical rules, and does not require tedious drill. It does not occur overnight, however. Real language acquisition develops slowly, and speaking skills emerge significantly later than listening skills, even when conditions are perfect. 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." (6-7)

Summary of Part I. Introduction: The Relationship of Theory to Practice

In deciding how to develop language teaching methods and materials, one can take three approaches: make use of second language acquisition theory, make use of applied linguistics research, and make use of ideas and intuition from experience. These approaches should in fact support each other and lead to common conclusions. This book incorporates all three approaches, with a hope of reintroducing theory to language teachers. While "most current theory may still not be the final word on second language acquisition," it is hoped that teachers will use the ideas in this book as another source alongside of their classroom and language-learning experiences.

Summary of Part II. Second Language Acquisition Theory

There are five key hypotheses about second language acquisition:


Adults have two different ways to develop competence in a language: language acquisition and language learning.

Language acquisition is a subconscious process not unlike the way a child learns a language. Language acquirers are not consciously aware of the grammatical rules of the language, but rather develop a "feel" for correctness. "In non-technical language, acquisition is 'picking-up' a language."

Language learning, on the other hand, refers to the "conscious knowledge of a second language, knowing the rules, being aware of them, and being able to talk about them." Thus language learning can be compared to learning about a language.

The acquistion-learning distinction hypothesis claims that adults do not lose the ability to acquire languages the way that children do. Just as research shows that error correction has little effect on children learning a first language, so too error correction has little effect on language acquisition.


The natural order hypothesis states that "the acquisition of grammatical structures proceeds in a predictable order." For a given language, some grammatical structures tend to be acquired early, others late, regardless of the first language of a speaker. However, as will be discussed later on in the book, this does not mean that grammar should be taught in this natural order of acquisition.


The language that one has subconsciously acquired "initiates our utterances in a second language and is responsible for our fluency," whereas the language that we have consciously learned acts as an editor in situations where the learner has enough time to edit, is focused on form, and knows the rule, such as on a grammar test in a language classroom or when carefully writing a composition. This conscious editor is called the Monitor.

Different individuals use their monitors in different ways, with different degrees of success. Monitor Over-users try to always use their Monitor, and end up "so concerned with correctness that they cannot speak with any real fluency." Monitor Under-users either have not consciously learned or choose to not use their conscious knowledge of the language. Although error correction by others has little influence on them, they can often correct themselves based on a "feel" for correctness.

Teachers should aim to produce Optimal Monitor users, who "use the Monitor when it is appropriate and when it does not interfere with communication." They do not use their conscious knowledge of grammar in normal conversation, but will use it in writing and planned speech. "Optimal Monitor users can therefore use their learned competence as a supplement to their acquired competence."


The input hypothesis answers the question of how a language acquirer develops competency over time. It states that a language acquirer who is at "level i" must receive comprehensible input that is at "level i+1." "We acquire, in other words, only when we understand language that contains structure that is 'a little beyond' where we are now." This understanding is possible due to using the context of the language we are hearing or reading and our knowledge of the world.

However, instead of aiming to receive input that is exactly at our i+1 level, or instead of having a teacher aim to teach us grammatical structure that is at our i+1 level, we should instead just focus on communication that is understandable. If we do this, and if we get enough of that kind of input, then we will in effect be receiving and thus acquiring out i+1. "Production ability emerges. It is not taught directly."

Evidence for the input hypothesis can be found in the effectiveness of caretaker speech from an adult to a child, of teacher-talk from a teacher to a language student, and of foreigner-talk from a sympathetic conversation partner to a language learner/acquirer.

One result of this hypothesis is that language students should be given an initial "silent period" where they are building up acquired competence in a language before they begin to produce it.

Whenever language acquirers try to produce language beyond what they have acquired, they tend to use the rules they have already acquired from their first language, thus allowing them to communicate but not really progress in the second language.


Motivation, self-confidence, and anxiety all affect language acquisition, in effect raising or lowering the "stickiness" or "penetration" of any comprehensible input that is received.

These five hypotheses of second language acquisition can be summarized: "1. Acquisition is more important than learning. 2. In order to acquire, two conditions are necessary. The first is comprehensible (or even better, comprehended) input containing i+1, structures a bit beyond the acquirer's current level, and second, a low or weak affective filter to allow the input 'in'."

In view of these findings, a question is raised: does classroom language teaching help? Classroom teaching helps when it provides the necessary comprehensible input to those students who are not at a level yet which allows them to receive comprehensible input from "the real world" or who do not have access to "real world" language speakers. It can also help when it provides students communication tools to make better use of the outside world, and it can provide beneficial conscious learning for optimal Monitor users.

Various research studies have been done comparing the amount of language competence and the amount of exposure to the language either in classroom-years or length of residence, the age of the language acquirer, and the acculturation of the language acquirer. The results of these studies are consistent with the above acquisition hypotheses: the more comprehensible input one receives in low-stress situations, the more language competence that one will have.

Summary of Part III: Providing Input for Acquisition

Once it is realized that receiving comprehensible input is central to acquiring a second language, questions are immediately raised concerning the nature and sources of this type of input and the role of the second language classroom.

To what extent is the second language classroom beneficial? Classrooms help when they provide the comprehensible input that the acquirer is going to receive. If acquirers have access to real world input, and if their current ability allows them understand at least some of it, then the classroom is not nearly as significant. An informal, immersion environment has the opportunity to provide tons of input; however, that input is not always comprehensible to a beginner, and often for an adult beginner the classroom is better than the real world in providing comprehensible input.

However, for the intermediate level student and above, living and interacting in an environment in which the language is spoken will likely prove to be better for the student, especially considering the fact that a language classroom will not be able to reflect the broad range of language use that the real world provides. The classroom's goal is to prepare students to be able to understand the language used outside the classroom.

What role does speaking (output) play in second language acquisition? It has no direct role, since language is acquired by comprehensible input, and in fact someone who is not able to speak for physical reasons can still acquire the full ability to understand language. However, speaking does indirectly help in two ways: 1) speaking produces conversation, which produces comprehensible input, and 2) your speaking allows native speakers to judge what level you are at and then adjust their speak downward to you, providing you input that is more easily understood.

What kind of input is optimal for acquisition? The best input is comprehensible, which sometimes means that it needs to be slower and more carefully articulated, using common vocabulary, less slang, and shorter sentences. Optimal input is interesting and/or relevant and allows the acquirer to focus on the meaning of the message and not on the form of the message. Optimal input is not grammatically sequenced, and a grammatical syllabus should not be used in the language classroom, in part because all students will not be at exactly the same level and because each structure is often only introduced once before moving on to something else. Finally, optimal input must focus on quantity, although most language teachers have to date seriously underestimated how much comprehensible input is actually needed for an acquirer to progress.

In addition to receiving the right kind of input, students should have their affective filter kept low, meaning that classroom stress should be minimized and students "should not be put on the defensive." One result of this is that student's errors should not be corrected. Students should be taught how to gain more input from the outside world, including helping them acquire conversational competence, the means of managing conversation.

Summary of Part IV: The Role of Grammar, or Putting Grammar in its Place

"As should be apparent by now, the position taken in this book is that second language teaching should focus on encouraging acquisition, on providing input that stimulates the subconscious language acquisition potential all normal human beings have. This does not mean to say, however, that there is no room at all for conscious learning. Conscious learning does have a role, but it is no longer the lead actor in the play."

For starters, we must realize that learning does not turn into acquisition. While the idea that we first learn a grammar rule and then use it so much that it becomes internalized is common and may seem obvious to many, it is not supported by theory nor by the observation of second language acquirers, who often correctly use "rules" they have never been taught and don't even remember accurately the rules they have learned.

However, there is a place for grammar, or the conscious learning of the rules of a language. Its major role is in the use of the Monitor, which allows Monitor users to produce more correct output when they are given the right conditions to actually use their Monitor, as in some planned speech and writing. However, for correct Monitor use the users must know the rules they are applying, and these would need to be rules that are easy to remember and apply--a very small subset of all of the grammatical rules of a language. It is not worthwhile for language acquisition to teach difficult rules which are hard to learn, harder to remember, and sometimes almost impossible to correctly apply.

For many years there was controversy in language-teaching literature on whether grammar should be deductively or inductively taught. However, as both of these methods involve language learning and not language acquisition, this issue should not be central for language teaching practice. There has similarly been controversy as to whether or not errors should be corrected in language learners' speech. Second language acquisition theory suggests that errors in ordinary conversation and Monitor-free situations should not be corrected, and that errors should only be corrected when they apply to easy to apply and understand grammatical rules in situations where known Monitor-users are able to use their Monitor.

There is a second way in which the teaching of grammar in a classroom can be helpful, and that is when the students are interested in learning about the language they are acquiring. This language appreciation, or linguistics, however, will only result in language acquisition when grammar is taught in the language that is being acquired, and it is actually the comprehensible input that the students are receiving, not the content of the lecture itself, that is aiding acquisition. "This is a subtle point. In effect, both teachers and students are deceiving themselves. They believe that it is the subject matter itself, the study of grammar, that is responsible for the students' progress in second language acquisition, but in reality their progress is coming from the medium and not the message. And subject matter that held their interest would do just as well, so far as second language acquisition is concerned, as long as it required extensive use of the target language." And perhaps many students would be more interested in a different subject matter and would thus acquire more than they would in such a grammar-based classroom.

Summary of Part V: Approaches to Language Teaching

Popular language teaching methods today include grammar-translation, audio-lingualism, cognitive-code, the direct method, the natural approach, total physical response, and Suggestopedia. How do these methods fare when they are evaluated by Second Language Acquisition theory? Each method will be evaluated using the following criteria:

Requirements for optimal input:

  • comprehensible
  • interesting/relevant
  • not grammatically sequenced
  • quantity
  • low filter level
  • provides tools for conversational management.


Grammar-translation usually consists of an explanation of a grammatical rule, with some example sentences, a bilingual vocabulary list, a reading section exemplifying the grammatical rule and incorporating the vocabulary, and exercises to practice using the grammar and vocabulary. Most of these classes are taught in the student's first language. The grammar-translation method provides little opportunity for acquisition and relies too heavily on learning.


An audio-lingual lesson usually begins with a dialogue which contains the grammar and vocabulary to be focused on in the lesson. The students mimic the dialogue and eventually memorize it. After the dialogue comes pattern drills, in which the grammatical structure introduced in the dialogue is reinforced, with these drills focusing on simple repetition, substitution, transformation, and translation. While the audio-lingual method provides opportunity for some acquisition to occur, it cannot measure up to newer methods which provide much more comprehensible input in a low-filter environment.


Cognitive-code is similar to grammar-translation except that it focuses on developing all four skills of language: speaking, listening, reading, and writing. Communicative competence is focused upon. Since the cognitive-code approach provides more comprehensible input than grammar-translation does, it should produce more acquisition, but other newer methods provide even more and have better results. Learning is overemphasized with this method.


Several approaches have been called the "direct method"; the approach evaluated here involves all discussion in the target language. The teacher uses examples of language in order to inductively teach grammar; students are to try to guess the rules of the language by the examples provided. Teachers interact with the students a lot, asking them questions about relevant topics and trying to use the grammatical structure of the day in the conversation. Accuracy is sought and errors are corrected. This method provides more comprehensible input than the methods discussed so far, but it still focuses too much on grammar.


In the Natural Approach the teacher speaks only the target language and class time is committed to providing input for acquisition. Students may use either the language being taught or their first language. Errors in speech are not corrected; however, homework may include grammar exercises that will be corrected. Goals for the class emphasize the students being able to use the language "to talk about ideas, perform tasks, and solve problems." This approach aims to fulfill the requirements for learning and acquisition, and does a great job in doing it. Its main weakness is that all classroom teaching is to some degree limited in its ability to be interesting and relevant to all students.


Total Physical Response, or TPR, involves the students listening and responding to commands given by the teacher such as "sit down" and "walk," with the complexity of the commands growing over time as the class acquires more language. Student speech is delayed, and once students indicate a willingness to talk they initially give commands to other students. Theory predicts that TPR should result in substantial language acquisition. Its content may not be always interesting and relevant for the students, but should produce better results than the audio-lingual and grammar-translation methods.


Suggestopedia classes are small and intensive, and focus on providing a very low-stress, attractive environment (partly involving active and passive "seances" complete with music and meditation) in which acquisition can occur. Some of the students' first language is used at the beginning, but most in the target language. The role of the teacher is very important in creating the right atmosphere and in acting out the dialogues that form the core of the content. Suggestopedia seems to provide close to optimal input while not giving too much emphasis to grammar.

What does applied linguistics research have to say about these methods? Applied research has examined the older methods of grammar-translation, audio-lingual, and cognitive-code much more than it has looked at the newer methods. There seem to be only small differences in the results of the older methods. While much research remains to be done, Total Physical Response and the other newer approaches "produce significantly better results than old approaches."

So what is better, the classroom or the real world? "Quite simply, the role of the second or foreign language classroom is to bring a student to a point where he can begin to use the outside would for further second language acquisition.... This means we have to provide students with enough comprehensible input to bring their second language competence to the point where they can begin to understand language heard 'on the outside'.... In other words, all second language classes are transitional."

In the real world, conversations with sympathetic native speakers who are willing to help the acquirer understand are very helpful. These native speakers engage in what is called "foreigner talk," not very different from the way that a parent would talk to a child.

Voluntary pleasure reading is also beneficial for second language acquisition, especially as the reader is free to choose reading material that is of interest and the proper level in order to be understood.

Taking content classes in the language that is being acquired can also be helpful to the more advanced learner, especially when the class is composed of students who are all acquiring the second language.

How does all of the above affect our views on achievement testing? As students will gear their studying to the type of tests they expect to take, the kinds of language tests that are given is very important. "Achievement tests...should meet this requirement: preparation for the test, or studying for the test, should obviously encourage the student to do things that will provide more comprehensible input and the tools to gain even more input when the class is over." With this in mind, general reading comprehension tests are helpful, as would be a test that would encourage students to participate in conversations and employ the tools of communicative competence.

Assuming that the conclusions in this book are correct, many new classroom language materials need to be developed. These materials should focus on providing much comprehensible input to beginning and intermediate students and should provide them with the means to gain even more input outside the classroom. Such materials should only focus on grammatical rules that are easy to learn and apply. Readers should have much more reading material in them and much fewer exercises and should have enough content that students can choose which topics to read about.

A quote from the conclusion:

"Even if the theory presented here is totally correct, and my suggestions for application are in fact the appropriate ones, there are some serious problems that need to be mentioned before concluding. These have to do with the acceptance, by teachers and students, of language acquisition as primary, and comprehensible input as the means of encouraging language acquisition. These problems are caused by the fact that acquisition differs from learning in two major ways: acquisition is slow and subtle, while learning is fast and, for some people, obvious.... I think that I have presented a conservative view of language acquisition theory and its applications, conservative in the sense that it attempts to be consistent with all empirical data that are known to me. It is consistent with the way thousands of people have acquired second languages throughout history, and in many cases acquired them very well. They acquired second languages while they were focused on something else, while they were gaining interesting or needed information, or interacting with people they liked to be with."