* An Overview of SLA


INTRODUCTION TO SLA (Adapted from Jordan, G. (2004) Theory Construction in SLA. Amsterdam: Benjamins.)

SLA theory attempts to explain the phenomena involved when a person acquires a second language. We observe that people whose native language is X acquire a second language Y: How do they do it? The point of this over–simplified description is to emphasise that any theory is an attempt to explain phenomena, and to highlight four key terms: phenomena; language; acquistion; and explanation.


The term phenomena refers to things that we isolate, define, and then attempt to explain. Examples of phenomena are volcanoes, tides, genes, hallucinations, warts, steam, the second world war, car rage, the beginning of the universe. We should note immediately that phenomena are not always directly observable: genes and hallucinations are two examples from the foregoing list, Chomsky’s LAD and “Interlanguage” are two more. The distinction between phenomena and empirical data, the latter being by definition observable, is an important one for any study of SLA.


In SLA the phenomenon which interests us is people being able to speak languages other than their own native language/s. How one describes that phenomenon is crucial to the subsequent investigation. Those taking a Universal Grammar (UG) approach to SLA, for example, say that the phenomenon to be explained is a certain type of knowledge, namely linguistic competence, and their research consequently involves describing this knowledge and explaining how it is acquired. There are others in the field of SLA, however, who wish to take a much broader view of SLA, who wish to investigate “communicative competence”, and language use. As a result, a wider range of phenomena need to be explained by appeal to individual differences among learners, social and cultural factors, and so on. We’ll look at all these views later on.


If breaking down the term “language” into better-defined competencies is an important step towards describing what is acquired in SLA, then similarly, when we ask the question “How is a second language acquired?” we need to take a similarly close look at the process of acquisition.

Long gives this description of SLA theory: “SLA theory encompasses the simultaneous and sequential acquisition and loss of second, third, fourth, etc. languages and dialects by children and adults learning naturalistically or with the aid of instruction, as individuals or in groups, in second or foreign language settings”. (Long, 1993: 225)

While Long’s description helps to give some idea of the breadth of SLA theory, it is useful to break the question of the process of acquisition down, so as to highlight the phenomena that we are interested in. I cite two, by no means definitive, lists. The first, by Towell and Hawkins (1994), identifies five core phenomena for which, they maintain, a theory of SLA must account:

1. Transfer – of grammatical properties from the L1 mental grammar into the mental grammar that learners construct for the L2.
2. Staged Development – L2 learners go through a series of “transitional stages” towards the target language, i.e. from the initial-state grammars that L2 learners construct (often heavily influenced by transfer) they subsequently go through stages of development towards the target language.
3. Systematicity – in the growth of L2 knowledge across learners, i.e. learners from different L1 backgrounds acquiring an L2 under different conditions of exposure – naturalistic versus classroom – often go through the same stages of development.
4. Variability – in learners’ intuitions about, and production of, the L2 at various stages of L2 development. These seem to allow for more than one variant for a given construction where the target language has only one form.
5. Incompleteness – most L2 learners do not achieve native-like competence. This phenomenon is referred to as fossilisation by Selinker (1972) and as incompleteness by Schacter (1990). (Towell and Hawkins, 1994: 15)

This list has a definite, explicit agenda, which is to argue for the key role played by Chomsky’s theory of UG. Towell and Hawkins argue that any approach to SLA that lacks “a sophisticated theory of the nature of grammatical structure” (Towell and Hawkins, 1994: 55) will not be able to offer a satisfactory explanation of these five phenomena. These phenomena would certainly not be the (only) ones listed by many working in the field today. Behaviourists, for example, would question the assumption of a developing interlanguage, and even within the “linguistic” camp, there are some researchers, as we shall see, who would not agree with the inclusion of Variability in the list.

Mitchell and Myles (1998), in their more general survey of SLA, describe the areas of interest in SLA research slightly differently, and identify four:

1. The role of internal mechanisms
a) Language-specific: how similar are 1st. and 2nd language acquisition processes? (Is UG available?)
b) Cognitive: is SLA similar to learning any other complex skill?

2. The role of the first language: the phenomenon of transfer.

3. The role of psychological variables: how do individual characteristics of the learner affect the learning process?

4. The role of social and environmental factors. (Mitchell and Myles, 1998: 40)


Having introduced the issues of what language might consist of, and the types of phenomena that might interest SLA researchers, we come to the term “explanation”. An explanation is generally taken to be an answer to a “Why” or “How” question about phenomena; it involves causation or a causal mechanism. Why do most L2 learners not achieve native-like competence? How do L2 learners go through stages of development? Explanation is said to be the purpose of a theory, and one of the most important criteria for judging theories is their explanatory power. We will need to examine what is involved in an adequate explanation later, but for the moment we can note that the best theories are the ones that provide the most generally applicable explanations: if we could construct a theory of SLA that explained the way in which anybody, anywhere, at any time learned a second language, and if that theory did not clash with the facts, we would have a very strong theory indeed.

It seems, then, that all we have to do is define the phenomena we want to explain, ask relevant questions, and then set about the search for the answers. While this may appear to be a straightforward task, and while it is all too frequent for researchers in this, as in other fields, to complicate the issues unnecessarily, the attempts to explain the phenomena of SLA have so far produced no satisfactory answer, i.e. there is no theory that covers all the phenomena, that fits the facts, and that is accepted by a majority of those working in the field.


What should be the objective of a theory of SLA? Two main questions need attention.

First, while most academics would agree that the main objective of a theory of SLA should be to explain the phenomena under investigation, the question remains: What counts as an explanation of SLA? This question, already briefly touched on above, permeates any discussion of theory construction; it involves issues such as research methodology, domain, and what might be appropriate questions for SLA researchers to ask. Some researchers, like Tarone and Ellis, regard their work as essentially descriptive: they observe classroom behaviour for example, and their objective is to find ways of providing an adequate description of what they observe. This essentially inductive approach to research is shared by many researchers in a wide range of fields; its conservative, methodical, painstaking approach is one of the most pervasive in the history of science. The objectives of a theory are seen, from this view, as discovering (uncovering), describing, making sense of the data. A different perspective, that taken in the field of SLA by researchers such as McLaughlin, Eubank, Skehan, Chaudron, and Gass, is that the objective of any theory is to provide a more general causal explanation of the phenomena. From such a perspective, without a causal explanation there is no theory, just (empirical) data and taxonomies.

Second, should an SLA theory aim to inform language teaching practice, or ignore such considerations? Again, the question greatly influences the way researchers approach theory construction. While this dissertation is solely concerned with SLA, which is just one part of the broader field of applied linguistics, van Lier’s comment echoes the concerns of many researchers in SLA: “The linguistics in AL has veered off in the direction of theory, … leaving pedagogy to cope with the practical side of things. There has occurred a sort of “double split” – linguistics (and SLA) with theory in one direction, and education with practice in another – and this split needs to be resolved before we can once again speak of a healthy AL”(van Lier, 1994: 30). There are those who would argue that there no such split exists (pointing to Robinson 2001, for example), and on the other hand, many researchers, particularly those working in a UG framework, argue that they have no necessary obligation to look for pedagogical pay-offs, and that their real purpose is to describe and explain certain phenomena.

Long’s position seems the most sensible. Long (1998) recognised the social responsibility researchers have to help improve the efficaciousness of classroom teaching and to forge a more liberal language policy, but at the same time defended the right of scholars to pursue “pure” research, where no practical payoff is foreseen. A related issue is to what extent one adopts a “realist” or an “instrumentalist” view of explanations.

The Domain of SLA

One of the main arguments among SLA researchers concerns what an SLA theory should or should not consist of, i.e. its domain. The choice of different domains reveals fundamental incompatibility. An example is Gregg’s attack (1990) on variable competence models (Tarone, 1988; Ellis, 1989), which Gregg thinks are totally mistaken because they confuse performance and competence, data and the phenomena to be explained. From Gregg’s UG perspective the domain of Tarone’s and Ellis’ models is irrelevant since performance is the data, and cannot possibly form part of the phenomena which a theory of SLA should explain.

Another increasingly important disagreement about domain concerns the role of sociolinguistics. Firth and Wagner (1997) have criticised SLA research for “ignoring social context”, and suggest that SLA research should give up its preoccupation with what goes on in the learner’s mind and pay more attention to social factors. Lurking behind this criticism is the related question of research methodology, as we shall see.

In fact, questions of the scope of an SLA theory are probably the most central to the research programme. What is the “L” in SLA? What is the competence that we seek to describe or explain? What is the role of UG? What else, apart from grammatical competence, should be included? What is the end state of SLA? What is the process of SLA? Do we need two theories to deal with the “L” and the “A” of SLA? Should an SLA theory attempt some overall explanation of an agreed list of phenomena like, for example, those already referred to, or should it shun the overall theory in favour of some partial explanation, concentrating on, for example, linguistic competence, or variability, and developing its own separate constructs and hypotheses?


Even within a particular domain, there are contradictory theories. Long gives some examples:

• Krashen’s Input Hypothesis (1980) (learners can only acquire new structures that are “one step ahead” of their current stage of development) clashes with Pienemann (1984, 1992), who made essentially the same claim in his Learnability and Teachability Hypotheses, but criticised Krashen on the grounds that the Input Hypothesis was not predictable or testable.
• Krashen’s dichotomous model versus several continuum models of interlanguage variation (see Tarone, 1983, for discussion).
• Conflicting views about access to principles of UG in adult SLA (Bley-Vroman 1989, Schwartz 1990).
• Sociolinguistically-based and cognitivist accounts of interlanguage variation (Sato 1984, Tarone 1988, 1989, Crookes 1989, Hulstijn 1989, Selinker and Douglas 1989).
• Linguistic and cognitivist explanations for observed developmental sequences (data on Swedish SL negation Hyltenstam 1977, 1982; Jordens 1980, 1982.)

Beretta (1993) agrees with Long, and argues that while complementary theories (theories operating in different domains and each providing answers to different parts of the SLA puzzle) are no problem (provided the complementarity is theoretically coherent), oppositional theories are a problem, since they offer theoretically incompatible, mutually exclusive explanations of the same facts. Moreover, like Long, Beretta sympathises with the view that different researchers from different traditions find it difficult to communicate with each other or to appreciate the significance of the questions being addressed. On this view, different theories are not just oppositional: they are, in Kuhn’s (1962) sense, incommensurable.

The three basic types of theories that Beretta sees as mutually exclusive are those dealing with cognitive, affective, or linguistic factors, respectively. Long and Beretta both believe that multiple theories like these indicate a very serious problem, since the theories are oppositional, and indicate that SLA theory construction is still immature – in what Khun (1962) would call a “pre-paradigm stage”. Long suggests that some culling is needed, firstly because we need to make progress so as to solve pressing social problems the appropriacy of different kinds of SL teaching or SL educational programs for learners of different ages and different L1 & L2 proficiencies currently have to be based in large part on SLA theory (Long, 1993: 229), and secondly because, following Kuhn (1962), the history of science shows that successful sciences are those which work (for most of the time) under a paradigm, or at least a very small number of dominant theories. As has already been mentioned, even these two points are controversial: many, like Gregg and Eubank, for example, do not agree that researchers have any duty to solve social problems, others, like Schumann and Davies, for example, do not think SLA should attempt to be a successful science, and others, Feyerabend, for example, do not agree with Kuhn’s account of the history of science or with the lesson which he draws from it.

Main Findings

This is taken from an article by F- Miles which can be found here: https://www.llas.ac.uk/resources/gpg/421

The two main, well documented findings of SLA research of the past few decades are as follows:
1. second language acquisition is highly systematic
2. second language acquisition is highly variable

Although these two statements might appear contradictory at first sight, they are not. The first one primarily refers to what has been called the route of development (the nature of the stages all learners go through when acquiring the second language – L2). This route remains largely independent of both the learner’s mother tongue (L1) and the context of learning (e.g. whether instructed in a classroom or acquired naturally by exposure). The second statement usually refers to either the rate of the learning process (the speed at which learners are learning the L2), or the outcome of the learning process (how proficient learners become), or both. We all know that both speed of learning and range of outcomes are highly variable from learner to learner: some do much better much more quickly than others.
Before we expand on these findings a little more, it is important to note that, traditionally, the concern for rate of learning has been the centre of teachers’ and learners’ attention. This is because it has obvious pedagogical implications: if we understand what makes learners learn faster and progress further, then maybe we can be better teachers or learners. However, these two lines of enquiry are both part and parcel of the same endeavour, which is to understand thoroughly how learners learn. In fact, understanding the route learners follow, and therefore having clear expectations of what learners can achieve at given points on the developmental continuum, is crucially important for both learners and teachers.

Such study leads us, for example, to a better understanding of the significance of errors in the learning process. Producing them need not be seen as necessarily problematic (in fact, some errors can be evidence of a more advanced linguistic system than the equivalent correct form: for example, learners will usually produce rote-learned formulaic questions such as ‘where’s X?’, e.g. ‘where’s the ball?’, in which ‘where’s’ is an unanalysed chunk, before producing the developmentally more advanced ‘where the ball is?’, the second stage in the development of the interrogative system before the final stage in which ‘where is the ball?’ is produced correctly; See e.g. Myles et al 1998 and 1999 for a discussion. This is often referred to as the ‘U shape of learning’, typical also of L1 learners, by which learners start with the correct rote-learned form, e.g. took, before over-applying the past tense rule and producing taked, prior to learning the exception to the rule and producing took again, creatively rather than rote-learned this time. Teachers will also be less frustrated, and their learners too, when they become aware that teaching will not cause skilful control of a linguistic structure if it is offered before a learner is developmentally ready to acquire it.

Now, of course, if we can speed up progression along the route that research has identified we need to understand how to do so. But understanding this route is inseparably bound up with clarifying the question of rapid and effective teaching. The robust research findings regarding the systematicity of the route followed by L2 learners do not have straightforward implications for language teaching, however. One logical possibility might be that curricula should closely follow developmental routes; this is not sensible however, given (a) the incomplete nature of our knowledge of these routes, (b) the fact that classrooms are typically made up of learners who are not neatly located at a single developmental stage, and (c) the fact that developmental stages typically contain non-target forms. (For example, typical stages in the acquisition of negation will be: 1. ‘no want pudding’; 2. ‘me no want pudding’ 3. ‘I don’t want pudding’, with forms 1 and 2 representing normal developmental stages, therefore to be expected in early L2 productions, but which will not be taught). Other possibilities are that curricula should be recursive with inbuilt redundancy, and that teachers should not expect immediate accuracy when teaching a new structure, or that they should give up on closely prescribed grammar curricula and opt instead for functional and/or task-based syllabus models. Many teachers/language educators have actively welcomed the role of ‘facilitator’ rather than ‘shaper’ of development, implied by such models.


There is little agreement among researchers in SLA about fundamental questions concerning how to construct a theory of SLA. In the rest of this section, in various bits, sooner or later, I will attempt to unravel the various threads running through the disagreements that exist about first principles, and suggest some ways in which those of us who agree to a minimally rationalist-realist approach can move forward. But don’t hold your breath.

See the References list in the Suggested Reading and References section for all works mentioned.

If you want just one book, I recommend:

VanPatten, B., & Williams, J. (eds.) (2007). Theories in second language acquisition. An introduction. Mahwah, NJ: Lawrence Erlbaum.

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