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Concourse 2

Theories of second-language acquisition (SLA)


This is an overview.  There are references at the end to further reading.



People have been learning and acquiring second (or third, fourth etc.) languages for thousands of years.  There's nothing new in that.
In many parts of the world, the ability to speak multiple languages is the norm not the exception.
In India, for example, Hindi, English, Bengali, Gujarati, Kashmiri, Malayalam, Marathi, Oriya, Punjabi, Tamil, Telugu, Urdu, Kannada, Assamese, Sanskrit and Sindhi are all official languages and it is not uncommon to find people proficient in more than two of them.
In South Africa, IsiZulu, IsiXhosa, Afrikaans, Sepedi, English, Setswana, Sesotho and Xitsonga are widely spoken and even in the USA (a country often assumed to be more or less monoglot) over 400 languages are spoken, some very widely, 170-odd of which are indigenous to the area.  A fifth of the US population uses a language other than English in the home.  In California, you can take your driving test in any of 32 languages.
Within Europe, a number of countries have more than one official language.  Switzerland is an obvious example but there are also four official languages in Austria, Germany and Spain, two in The Netherlands, two in Finland and so on.  100 languages are spoken across the UK and one in five of London's population does not have English as a first language.  The UK, oddly, does not even have an official language although 98% of the population speak English.
We should not, therefore, see the acquisition of an additional language as in any way exceptional.


Four important concepts

What is newer is the study of how second languages are learned or acquired.  To understand the underlying theories, it is useful to have a set of thinking tools to hand and that means understanding four elemental concepts.

Competence vs. Performance
Ferdinand de Saussure, in his Course in General Linguistics (1915) distinguished between langue (roughly the internal rules and arrangements of a language) and parole (roughly the spoken and written forms of language seen in everyday settings).
Chomsky, much later (1965 / 2002), made a similar distinction between Competence and Performance.
Competence is the speaker's general, implicit and rarely articulated, knowledge of the grammar of a language and Performance is the speaker's actual use of the language in speaking and understanding it.
Chomsky was not concerned so much with what is actually said but with what can be said.
The difference between the two divisions is that de Saussure was concerned with language in society but Chomsky was more concerned to explain individuals' use of and knowledge about the form of language.
For more on Chomsky's theories see the guide to Chomsky, linked in the list of related guides at the end.
Use vs. Usage
This distinction was first proposed by Widdowson (1978) and refers to the difference between the formal structures of the language and the language as it is used in real communication for authentic purposes.
Briefly, the distinction rests on the difference between signification (what, on the face of it, an utterance means) and value (what it means in communication).  So for example, if someone says
    I have a terrible headache
and the reply is:
    It's nearly 6 o'clock in New York
while we know what the words mean (the significance), they carry no communicative value.
If, on the other hand, the reply is:
    I'll get you something for it
then the response carries both significance and communicative value.
Much research into second-language acquisition is concerned with usage (how people acquire the formal systems of the language) and less effort has been devoted to how learners acquire the ability to use the language to get things done.
English language teachers are concerned with both significance and value, of course.
Acquisition vs. Learning
This distinction is attributed to Krashen (to whom there is a separate guide on this site, linked below).
Acquisition is a process similar to the way in which children acquire their first language(s).  It requires meaningful and frequent interaction in the language in which the speakers are not focused on form but on meaning.
Learning is, in contrast, a formal procedure which focuses on the explanation of rules and correction of language form.
It should be noted that Krashen was not explicitly stating that one is necessarily better than the other.
The distinction can be extended to the difference between naturalistic acquisition and instructed acquisition.  The former refers to the almost unconscious picking up of a language and the latter to the deliberate choice to study and be formally taught.
Deductive vs. Inductive processing
Deductive processing involves the application of given rules to the data.
For example, once you have been made aware that putting the right ending on a German verb in the second person singular (familiar) is to substitute -st for -en then you can transform any number of infinitive forms in the correct way to get, e.g.,
    rauchen – rauchst
    bringen – bringst

and so on.
Inductive processing works the other way around.
Given the examples of the transformation above and some more examples, such as
    reisen – reist
    denken – denkst

You can figure out for yourself what the rule is.
(You will not, by the way, be right for all the verbs in the language and this won't help you much with meaning but you will, one way or another, have learned a useful rule.)
Much nonsense is spoken about taking either an inductive or a deductive approach to learning.  This is not an either-or distinction.  Even if one starts with a purely inductive approach in the classroom, the aim has to be for the learners to hypothesise a rule (preferably the right one) and then apply it to further examples of the target language.  The second procedure is, of course, purely deductive.  There is little point in putting learners to the trouble of constructing a rule from exemplification if they are not then encouraged to apply it.
On the other hand, starting with a deductive approach and supplying a rule from the outset nearly always results in the need to refine the rule later to take account of more complex forms.  Even if we knew what they are, it would not be possible to supply all the rules for using, say, verb tenses in English so any rule which is presented to learners has to be no more than an approximation.
The situation is a bit like this:
and nobody yet knows the TRUTH, however sure of themselves they sound.


Internal factors

At the heart of all theories of SLA lie considerations of what the learner brings to the process and what role external factor play in it.

The starting point is the distinction between learning as a cognitive, conscious mental process and learning as a process of acquiring good habits.



It is well attested that one can teach rats (and all sorts of other creatures) by a process of stimulus and reward.  Rats, famously, can be taught complex sequences of behaviour such as finding their way through a maze based purely on rewarding, i.e., positively reinforcing, certain behaviours and punishing, i.e., negatively reinforcing, unwanted behaviour.
The theory relies heavily on work by, inter alia, Skinner (1957: 10) who is often quoted as saying:

We have no reason to assume ... that verbal behaviour differs in any fundamental respect from non-verbal behaviour, or that any new principles must be invoked to account for it.
(Skinner 1957: 10)

Behaviourism is the theory of learning that still underlies how you train your dog or drill your learners' pronunciation.  It can be visualised like this:


Briefly, and somewhat unscientifically:

  1. The process starts with a stimulus, say, a question from the teacher such as
        Where did you go yesterday?
    put to the organism (in this case, a learner of English).  The stimulus can elicit a variety of responses but only the 'right' one will be reinforced.
  2. So, for example, if the organism responds with
        I go to the cinema
    the teacher will negatively reinforce it with
        No, that's wrong
    or simply not reinforce it by saying nothing.
  3. If, on the other hand, the organism produces the preferred response:
        I went to the cinema
    the teacher will reinforce it with
        Yes, that's right!
    (preferably in a loud and enthusiastic voice because the strength of the reinforcement is critical in instilling the correct habit).  In this case, the reward is the teacher's approval but it could just as well be a chocolate biscuit.  The response does not have to be truthful, just well formed.
  4. Enough Stimulus > Response > Reinforcement cycles will see the habit instilled and the language acquired.

These are factors internal to the learner but they have significant implications for external factors such as the approach to teaching.  It underlies drilling language in the classroom, setting mechanical (and not so mechanical) exercises, exposing learners to patterns of language, repetition of language, the avoidance of error and much else.



Much research in the 1970s and later was focused on a determination to refute a behaviourist view of language learning and acquisition.  Three main lines of attack emerged.

The triumph of a more cognitivist view of language learning led to a number of competing hypotheses concerning how SLA occurs.  The initial attempt was to focus on internal factors but they all have significant external implications to do with presumptions concerning how language learning should take place to which we shall come.

In addition to these basic distinctions, it is now necessary to add several other theories and ideas.  Most of these concern theories of first language acquisition and are dealt with in a little more detail in the guide to first- and second-language acquisition, linked below.


Error analysis

The analysis of learners' errors starts with seminal work by Pit Corder (1981) who set out to investigate how the errors that learners make reflect their internal mental processes.
The key concept is interlanguage.

Interlanguage can be visualised like this where the learner's current knowledge lies somewhere on a continuum from knowing nothing about the target language to full mastery:


The diagram oversimplifies and hides some interesting ideas concerning the sources of error and the current state of the learners' knowledge.
What studies showed was that although some errors were the result of applying first-language rules to the target language (which would indicate the transfer of language habits), some errors indicated that learners were creatively constructing rules and hypotheses to explain the data to which they were exposed.
If this is the case, then teaching needs to address the positive role of error, the concept of noticing the difference between one's own output and native-speaker models and the supply of adequately rich linguistic data for the learners' cognitive processes to work on.
For a little more, see the guide to first- and second-language acquisition, linked below.


Acquisition order

Claims have been made that structural elements of a language are learned or acquired in a sequence which is remarkably stable across learners with a wide range of language and learning backgrounds.  Of late, enthusiasm for the idea of a fixed acquisition order has waned although there are some who still hold to it.
The jury is still out but there is undeniably some evidence that the phenomenon is real.  What has become clear is that teaching the target structures for which the learners are ready will be more effective than trying to impose a syllabus to beat the system.


Universal Grammar and the Language Acquisition Device

The essentials of these two ideas are covered in the guide to Chomsky so, in brief:

For more on these twin concepts, see the guide to Chomsky, linked below.


Active Construction of Grammar and Connectionist Theory

Because it may be the case that both these mechanisms are functioning simultaneously, we'll consider them together.

It is clear as far as teaching the language is concerned that for either of these theoretical mechanisms to function efficiently, the data presented to learners has to be orderly and rich enough for them to form hypotheses effectively and adapt them appropriately as new data become available.
For a little more in this area, see the guide to first- and second-language acquisition, linked below in the list of related guides.


Social constructivist theory

It has sometimes been a criticism levelled at a communicative approaches to language teaching that while the approach has a well worked out theory of language, it is less certain about a theory of learning.  Enter social constructivism to the rescue.

Briefly, the theory states that learning is constructed by the learners.  This is usually contrasted in educational theory with what is labelled as a transmission model in which knowledge is handed down from above.
The criticism of that is, naturally, that social constructivists are setting up an unrealistic 'traditional' model in order to suggest how social constructivism is superior.
It is, moreover, asserted that learning is primarily a social activity.  This means that knowledge and skills are not acquired by individuals operating alone but only through interaction with others.
This makes the theory a good fit with communicative classroom approaches which forefront real communicative tasks and emphasise interaction with peers and others.

Unfortunately, the theory is somewhat silent concerning the mechanisms through which learning takes place (unlike, e.g., connectionist and active construction theories).  It may, therefore, be wise to reserve judgement or, at least, to take the view that while social interaction is undoubtedly a useful and motivating factor in second-language acquisition, it cannot be the whole truth or individual silent learning would be impossible.  If you are reading this page alone, is it the case that you are unable to learn from it because you are not interacting with others?

Such considerations have not stopped some from asserting that social constructivism is the way in which learning happens.
Here's an example:

We believe that learning is best conceptualised through a social constructivist theory of learning.  A key tenet of this is the view that learning is constructed by the learner, as opposed to the traditional, “transmission” model of teaching and learning in which knowledge is passed on to students fully formed, ready to be assimilated.  Furthermore, learning is primarily a social activity – knowledge and skills are constructed through interaction with others.
Harrison, 2019 (Senior Education Manager, Cambridge Assessment English)

We need, however, to maintain a certain objectivity in this regard, too.  Constructivism is not a proven fact or even as yet elevated to the status of a theory.  It is one of many hypotheses about how language is learned.


Here's an incomplete summary of four major hypotheses concerning second-language acquisition.  It is not meant to show that learners use only one approach.  Some may use all four.

sla theories


External factors

There are also a number of factors external to the learner which need to be considered, if only briefly.


Social factors

Much of Communicative Language Teaching lays great stress on natural and appropriate language as the target of instruction.
It follows that in order to be able to acquire pragmatic as well as formal competence in a language, learners need to be exposed to appropriately complex social situations in which the target language is set.
Similar connectionist and active construction mechanisms may also be at work here as the learners refine their hypotheses about what is socially appropriate to realise a particular language function and what is statistically the most frequent way of doing so.
Also in play here are motivational issues.  Gardner (1985), for example, emphasises the role of learners' attitudes to the culture in which the second language is set.  Those who perceive it as high status and desirable will have greater integrative motivation and be more successful in acquiring the language whereas those who remain isolated from the target-language culture, or even indifferent or antagonistic to it, tend to develop only a very basic competence.
For more, see the guide to motivation, linked below.



The behaviourist view of input in the language learning process was that the input had to be very carefully tailored to the learners' current competence and, by a process of repeatedly encountering the data and repeating language in bite-sized doses, learning and competence would follow.  This is the underlying theory that gives rise to drilling and very controlled oral and written language practice.
The approach has been challenged in two ways:

The underlying assumption here is summarised by Waters as:

... learning occurs when the mind makes connections between what it already knows and new, hitherto unknown items of information
(Waters, 2006:319)

In other words, if the level of challenge is correctly set, learning will occur by extension and connection.  Stretched too far, learners will fail to see the connections.  Challenged too little and learners will not make new connections at all.
Linked below is a guide to a key set of concepts in this regard: Bloom's taxonomy of educational objectives which is an attempt to categorise cognitive challenge on a six-point scale from simple remembering to creating new syntheses.
There is a guide on this site to scaffolding, the ZPD and Vygotsky, linked below.
Motivation is also a significant factor and there is a link to a guide to that, in the table below.


Healthy, critical scepticism

This guide has been a brief one and only covered the salient features of a range of popular answers to the question
    How do people learn a language?
You will have noticed that some theories are presented as take-it-or-leave-it choices but reality is probably a little more complicated.  Humans are complex animals with the capacity for complex behaviour and ways of thinking about the world.  To aver that all of them learn all facets of all languages in the same way is much more likely to be wrong than right.
It may turn out to be the case, for example, that we learn grammar in one way, pronunciation in another and lexis in a third way and that has, in fact been suggested.  The suggestion, again briefly, is that:

  1. We learn grammar by a process of actively constructing and amending hypotheses about the way the language we have encountered works.
  2. We learn lexis through a process of making connections from the known to the unknown and taking the trouble to see how meaning is used in the language we encounter.
  3. We learn to pronounce the target phonemes in a language by a process of habituating ourselves to making certain (to us) unusual sounds and imitating what we hear.
  4. We learn to communicate using appropriate styles and registers in a process of constructing meaning socially with other humans.

If this is the case or even part of it is true, looking for a theory which explains all learning is a doomed undertaking.  Worse, it will constrain teachers' behaviours and planning to a degree which will not be helpful to the learners.

If you would like to take a simple test to check you have key concepts clear, there is one here.

moving on

Moving on

All the above concerns some quite rarefied theory but a good theory has practical implications and advantages.

You may like now to consider some other guides on this site to more practical matters, some of which have been mentioned.

Related guides
first- and second-language acquisition theories about how we learn our first language and how they may apply to SLA
Chomsky Transformational Generative Grammar, Competence and Performance, the Language Acquisition Device and Universal Grammar
Krashen and the Natural Approach the five central hypotheses, The Natural Approach in practice and criticisms of the theory
motivation Gardner's four motivational categories, Expectancy Theory and Task, Institutional and Global motivation
error categorising error, the role of error in learning, interlanguage
the history and development of English Language Teaching the ways in which theories of language and theories of learning have developed and informed ELT methodologies
scaffolding a guide which includes considerations of the ZPD and Vygotsky's theories
input the nature of input and how input may become intake and output
noticing how learners refine hypotheses based on what they see and hear
inferencing for a little more about how we use statistical reasoning to understand language
Bloom's taxonomy this takes a severely cognitive view of learning and attempts to rate cognitive challenge on a six-point scale
unlocking learning this is a guide in the Delta section which considers four theories and their classroom implications for learning

Bergmann, A, Hall, K & Ross, S (Eds.), 2007, Language files: Materials for an introduction to language and linguistics, Columbus, Ohio: The Ohio State University Press
Chomsky, N, 2002, Syntactic Structures (2nd Edition), New York: Mouton de Gruyter
Corder, SP, 1981, Error analysis and interlanguage, Oxford: Oxford University Press
de Saussure, F, 1986, Course in general linguistics (3rd Edition). (R. Harris, Trans.), Chicago: Open Court Publishing Company.
Gardner, RC & Lambert, WE, 1972, Attitudes and motivation in second language learning, Rowley, MA: Newbury House
Gardner, RC, 1985, Social Psychology and second language learning: The role of Attitude and Motivation, London: Edward Arnold
Harrison, G, 2019, Developing teachers: key principles in the Cambridge English approach to teacher education, Cambridge: UCLES, Professional development, Teaching (available at: https://www.cambridgeenglish.org/blog/developing-teachers [accessed October 2021]
Hymes, D, 1971, On communicative competence, in Pride, J & Holmes, J (Eds.), Sociolinguistics, London: Penguin
Lyons, J, 1970, Chomsky, New York: Viking Press
Skinner, BF, 1948, Verbal Behavior, retrieved from http://www.behavior.org/resources/595.pdf
Vygotsky, L, 1962, Thought and Language, Cambridge, MA: MIT Press

Waters, A, 2006, Thinking and language learning, in ELT Journal Volume 60/4, Oxford: Oxford University Press
Widdowson, HG, 1978, Teaching Language as Communication, London: Oxford University Press