The relationship between first and second language acquisition

The Relationship between First and Second Language Learning Revisited

Draft of chapter in Macaro, E. (ed.) The Continuum Companion to Second Language Acquisition, Continuum, 137-157, 2010 (some typos corrected and links added, 2019)

The relationship between how people learn their first language (L1) and how they learn their second language (L2) and subsequent languages has concerned second language acquisition (SLA) research ever since it became an independent discipline (see Stern, 1967; Cook, 1969, 1973; Ervin-Tripp, 1974 for a selection of early views). The relationship between the two languages is crucial because it defines the very nature of second language acquisition: if L2 acquisition did not differ in some way from L1 acquisition, SLA research would be merely a sub‑field of language acquisition research rather than a field of its own. It is a truism that the defining characteristic of L2 acquisition is the presence of a second language in the same mind as a first and that the characteristic of an L2 community is the use of additional languages to the first language. The unique problem for SLA research is to see how this pre-existing language affects the L2 user's mind and the L2 user's community.

This chapter concentrates on the language of the individual rather than of the community. It shows how SLA research emerged out of the chrysalis of L1 acquisition research, looking particularly at acquisition stages and at research techniques. Then it links three contemporary L1 approaches to questions relevant to SLA research. Next it looks at the differences and similarities that have been proposed between L1 and L2 acquisition. Finally it concludes with a plea for the independence of SLA research from L1 acquisition research.

Early SLA research in the 1960s drew on first language acquisition research not only for its ideas but also for its research techniques. The dangers are using ideas and techniques that do not transfer to L2 acquisition for various reasons and employing them long after their sell-by date in L1 acquisition research.

The mainspring that drove SLA research in the 1960s was the independent grammars assumption as applied to children's language by people such as Brown (1973) and McNeill (1966): children should not be treated as mini-adults but as children. The child's language constitutes an independent system of its own rather than being a defective version of the adult system. Braine's crucial work with two-word sentences set the trend (Braine, 1963). Children's utterances like more high were not deformed versions of adult sentences but reflected the unique pivot-open organisation of early child grammar; to make a two-word utterance, combine a pivot word like more with a content word like high, yielding more high, a request to be lifted up. Children's sentences are not poor attempts at adult sentences but proper sentences according to the child's own rules.

Taken into SLA research, the independent grammars assumption became known as the 'interlanguage' hypothesis: 'the existence of a separate linguistic system' (Selinker, 1972). The learner's language system is not a defective version of the native speaker's but a developing system in its own right. This concept served to liberate SLA research from the dead hand of structural linguistics and Contrastive Analysis by starting from the learner rather than a preset apparatus. The main focus became the detailed analysis of learners' speech, in principle independently of the language of native speakers. You no longer had to compare the total syntax and phonology of the two languages before you tackled L2 learning as it were but could start in on what actual learners did and see what there syntax and phonology consisted using the learners' own speech or writing – in a sense a bottom-up data-led process rather than a top-down theory-based one.

Yet, despite paying lip-service to interlanguage, the vast majority of SLA research never quite accepted the interlanguage assumption that learners have to be studied in their own right. In L1 acquisition research, people had indeed knuckled down to the task of looking at the child's own language development rather than looking for deviations from adult speech, as most introductions to L1 acquisition show to this day, say Bloom (2002) and Clarke (2003). L2 learners, however, were at every turn measured against the monolingual native speaker, both overtly as shown by remarks like 'Relative to native speaker's linguistic competence, learners' interlanguage is deficient by definition' (Kasper & Kellerman, 1997, 5), and covertly through research techniques such as grammaticality judgements that implicitly use the native speaker as a touchstone.

The most influential concept taken from L1 acquisition research was undoubtedly that of developmental sequence. L1 children were believed to progress through distinct stages in language acquisition, just as their cognition developed through stages whether those of Piaget (Piaget & Inhelder, 1969) or Bruner (1966). Brown (1973) made the first major longitudinal study of the language of three children, followed by Gordon Wells' monumental attempt at recording 124 children (Wells, 1981) and Bruner's observations of 120 children (Bruner, 1983). In a sense such longitudinal projects aimedc at establishing the stages of development; what does the child learn first, second, …? Explanations of the sequence were tagged on post hoc after the basic developmental 'facts' had been described, whether the semantic explanations of Brown, the functional theories of Wells or the social interaction of Bruner.

Dulay and Burt (1974) applied the Brown study techniques to the L2 development of so-called grammatical morphemes such as prepositions to and in and grammatical inflections such as –ing and 's. They found evidence for an L2 sequence that was similar to but nonetheless distinct from the L1 sequence in Brown (1973). Sequence of acquisition has dominated SLA research ever since; massive efforts have gone into investigating which sounds are learnt first (Major, 1994), which syntactic structures (Zobl & Liceras, 1994), and countless other areas. The order in which things are acquired is then taken to be the crucial evidence for language acquisition. Few L2 studies have looked at overall development through longitudinal corpus studies, apart perhaps from the work of the ESF project with migrant workers (Klein & Perdue, 1997) or Wode's study of his children (Wode, 1981). The L2 explanations for the order of L1 development either deny the need for an explanation as it is just 'natural', as in the Natural Order Hypothesis (Krashen, 1985), or are based on a single aspect of development, whether the social cognitive dimension of the ESF (Klein & Perdue, 1997) or the parameter setting/resetting of the Universal Grammar generativists (White, 2003).

Hardly anybody seems to have taken heed of Chomsky's insistence that it is the acquired knowledge that is crucial, not the order in which it is acquired. He has often spoken of an idealised 'instantaneous' model of language acquisition that relates language input and competence as wholes without reference to chronological development (Chomsky, 1986). Cook and Newson (2007) distinguish acquisition – the logical problem of how the mind acquires language independent of intervening stages – and development – the history of the intervening stages. As a car-driver, it does not matter to you in which order you learnt to steer, use the brake, change gear etc. It's what you can do that is important, not which component you learnt first, even if there is presumably a natural sequence for learning to drive. Developmental order in the first language may be the product of factors other than language acquisition per se, such as frequency effects in the language input, the development of the child's working memory, and so on. Teasing out language acquisition from these other factors is a major task for L1 acquisition research.

Nor is the concept of stage itself clearly defined. Ingram (1989) found several types of L1 'stage' – a 'continuous stage' referring to 'a point on a continuum', a 'plateau stage' where change halts for some time, a 'transition stage' before change takes off again, and an 'acceleration stage' where there is rapid acquisition before reaching a plateau. Most SLA research such as Dulay and Burt (1974) has used the continuum meaning; a stage has no coherent characteristics of its own other than its position on the continuum; one thing just comes after another. Processability theory (Pienemann, 1998) is like more a plateau and transition stage theory with broad characteristics for each stage. Saying that language acquisition proceeds through stages of development is empty without defining what a stage is.

One crucial question to be developed below is whether the L2 user's knowledge of the second language is the same as that of an L1 monolingual native speaker of that language. The main question for many researchers has been whether the stages and processes through which L2 learners develop are the same as those for L1 children. SLA researchers were impressed by the overall idea of sequence: the discovery of a common acquisition sequence for L2 learners is 'surely one of the most exciting and significant outcomes of the last decade of second language research' (Dulay & Burt, 1980). Experiments indeed showed that L2 learners acquired things in a sequence resembling L1 acquisition. Like L1 children (Cromer, 1970), L2 users first confused the difference between John is easy to please and John is eager to please and sorted it out comparatively late (Cook, 1973; [later Cook. 2003]) – plateau stages with transitions – despite having no clear way of deriving the structure from the speech that they encounter. The importance of stagiation depends on whether you accept that the route is important rather than the process or the target. I can walk to work, or go by bicycle or by car, with slight variations according to one-way streets and pedestrianised areas etc, but does it matter what I do so long as I get there?

As a new area of research, SLA research undoubtedly borrowed most of its research techniques from first language acquisition and has continued to do so. After all, why not? Both disciplines are concerned with language acquisition; it would be surprising if techniques that worked in one area did not work in the other; it's the same human mind acquiring language in both cases after all. A useful practical survey of the main L1 research techniques is provided in McDaniel et al (1996).

The techniques most obviously borrowed from L1 acquisition research are those for studying actual sentences that L2 learners produce, which we can call natural data (Cook, 1986). The L1 corpus studies by Brown (1973) and Wells (1981) recorded children's sentences over a period of years and analysed them in terms of mostly syntactic criteria. In SLA research the ESF project adopted a similar approach by recording large amounts of speech by immigrants to five countries and producing an account of the learners' common basic grammar and semantic stages through which they progressed (Klein & Perdue, 1997).

SLA research was also fond of a technique for tackling natural data called Error Analysis (EA) (Corder, 1971). This looked at the differences between the learners' speech and that of native speakers and then looked for explanations. However, EA fundamentally differed from the children's corpus analyses in that it looked for 'errors', defined as deviations from native speech – 'the methodology of description is, needless to say, fundamentally that of a bilingual comparison' (Corder, 1971). EA in the main tried to find the origins of errors in the knowledge of the first language, an explanation that was clearly not possible for L1 researchers. Indeed the very concept of 'error' in L2 speech seems in breach of the interlanguage assumption unless highly qualified.

Another popular technique with natural data was scoring obligatory occurrences of particular syntactic forms. Brown (1973) had defined 'obligatory' in terns of context; in some sentences the linguistic context makes you supply a demonstrative that – that man – or the prior context shows that you must say the man, not a man, and so on. The continued use in SLA research from Dulay and Burt (1974) to the Competition Model (Pienemann, 1998), however, defines obligatory as what a native speaker would say – again the native speaker sneaking in by the back door.

The second broad family of techniques borrowed from L1 research generated controlled data (Cook, 1986). One form this takes is getting learners to produce naturalistic speech. For example Slobin and Welsh (1973) devised the elicited imitation technique which asks L1 children to repeat sentences; the ways in which they change the sentence are believed to reveal properties of their underlying competence. Elicited imitation was used for second language acquisition by Cook (1973) for testing the comprehension of relative clauses, and by many others. Eliciting sentences through picture description was also used by for example Bellugi and Brown (1964) for L1 plurals and by Dulay and Burt (1974) for L2 grammatical morphemes. Various ways of getting people to talk have been used ever since, for instance the well-known 'danger of death' question pioneered by Labov (1984), 'When did you come closest to dying?'.

An important additional source of information for SLA research is introspection data (Cook, 1986). L2 learners are asked about their emotions, motivations and strategies, surveyed in say Dornyei (2006) or McDonough (1981). Much of this data is unobtainable in L1 acquisition as the children's age makes such testing virtually impossible. One key technique in SLA research has been grammaticality judgements, the vital technique used in generative SLA research. L2 learners are asked whether they feel that certain sentences are grammatical or not and their answers compared with those of native speakers, explicitly or implicitly as in say Hawkins and Chen (1997).

L1 research has mostly eschewed testing the grammaticality judgements of young children, partly because of doubts about what these judgements actually mean, partly because of the difficulty of administering them, though they are stoutly defended by McDaniel et al (1996) provided they are carried out in a way that makes sense to the child. Despite this, Muhammad Hannan (2004) used grammaticality judgements to find an L2 sequence of acquisition for Bengali-speaking children in East London. By and large grammaticality judgements as an L2 research technique cannot be justified from L1 acquisition research – for good or for ill. Nor can they claim their justification from the linguist's non-experimental use of linguistic intuitions, a different approach to evidence. And they are suspect for comparing L1 and L2 learning because one of the things that changes in L2 learners is precisely the ability to treat language metalinguistically (Bialystok, 1993).

Let us now turn to some current views of how children acquire their first language to second language acquisition before relating them to second language acquisition.

Since the mid 1990s an influential psychology theory has been called usage-based linguistics, among other names. As described by Tomasello (2003), this has two important components: intention-reading and pattern finding, which reappear in different guises in other forms of cognitive psychology.

Intention reading refers to the well-documented ability of young children to see the world from another's point of view. Trevarthen (1974) filmed mothers talking to babies face to face. When the mother started to look over the baby's shoulder, the baby would try to turn to see what the mother was looking at. Simple enough but a clear sign of being able to see things from another point of view: if I were my mother, moving my eyes would mean I was looking at something; therefore there is something to be seen if I turn round. Another example is the well-known false belief test, which has many variations. Typically two girls called Sally and Molly are in the same room with the experimenter. Sally hides a teddy bear under a chair; Molly goes out of the room; Sally picks up the bear and hides it under the table; the experimenter asks Sally 'Where does Molly think the bear is?'. If Sally says 'under the chair', she can see the other's point of view; if Sally says 'under the table', she cannot. Tomasello (1999) explores variations on this task, showing time and again that the child knows how other people see the world – a so-called 'theory of mind' (TOM). The crucial thing for language acquisition is then being able to see the world from another point of view; lack of a theory of mind is one of the causes of autism (Baron-Cohen, 1995). Hence the language interaction formats described by Bruner (1983) are a way of developing the child's theory of mind, of enabling him or her to see how an adult views the world.

Looked at from an SLA perspective, the L2 learner no longer needs to go through this process; L2 learners already have a theory of mind and do not need to develop it over again. Goetz (2003) has shown that young L2 learners pass such theory of mind tests earlier than monolinguals; learning a second language provides an initial impetus to getting a theory of mind. Children who were bilingual in pairs of spoken and sign languages such as Italian/Italian Sign Language and Estonian/Estonian Sign Language were better at TOM tasks than those raised with only a single language (Meristo et al, 2007). L2 learners may go a stage beyond a theory of mind to a theory of minds: monolingual children may get the impression that all other minds have a similar point of view; bilingual children or adults are soon convinced of the multiplicity of points of view.

This topic introduces a leit-motiv for this chapter: the L1 child's maturation is a transforming experience that does not need to be repeated by older learners in a second language, or indeed cannot be repeated. Stages of acquisition may be non-reversible, if they depend on cognitive or social maturation; you don't lose TOM in a second language. Gleitman (1982) introduced the metaphor of frogs and tadpoles into language development: once a tadpole transforms into a frog, the process cannot be reversed. It may be that language and other cognitive processes are transformations of this kind; you can't change back into an earlier version of yourself, whatever beauty products may try to hint. Indeed I once conducted an experiment with hypnotic age regression that tried to demonstrate that adults could not speak like five-year-olds, alas abandoned for methodological and ethical reasons.

Language is for doing things and for relating to people. Halliday (1975) saw children's development in terms of the functions they want to express, initially starting with six distinct functions, gradually developing into the three simultaneous adult functions – the interpersonal (relating to people), the ideational (communicating ideas to other people) and the textual (relating one piece of language to another). The fundamental issue is 'learning how to mean' – discovering how to use the multiple functions of language.

Social theories of language therefore imply the first language emerges through interaction between children and adults. Different social functions have been emphasised from time to time. Adults for example use a particular style of language when talking to children, say speaking more grammatically and using baby-talk vocabulary like 'bow-wow' (Snow & Ferguson, 1977). Certain kinds of interaction are favoured; Bruner (1983) for instance documented the development of peekaboo games. Others have looked at characteristics of child-adult exchanges; Bellugi and Brown (1964) highlighted a process of 'imitation with expansion' in which the adult repeats back the child's sentence in a slightly different form,
Child: Baby highchair
Mother: Baby is in the highchair
These came subsequently to be called 'recasts'. These interactional devices clearly depend on the child having a theory of mind; nothing would be gained from recasts if the child reacted by thinking 'Why is this stupid person repeating what I say?'

SLA research has usually translated parent/child interaction into native speaker (NS) to non-native speaker (NNS) interaction. Recasts have featured highly in classroom interaction, defined as 'the teacher's reformulation of all or part of a student's utterance minus the error' (Lyster & Ranta, 1997, 46). Han (2002) suggested that the success of recasts depends on intensity of instruction and developmental readiness. Often recasts have been linked to Vygotsky's 1930s theory of child development (Vygotsky, 1934/1962, 1935/1978), a precursor to modern ideas. The main construct has been the ZPD (Zone of Proximal Development), in SLA research taken to be the gap between the learner's current stage and the next point on some developmental scale (Lantolf, 2000). Yet, like the theory of mind, this brings to light a distinct feature of second language acquisition: whatever L2 learners need to learn it is not how to mean. They have learnt the functions of language itself along with their first language; they simply have to discover how second language exploits this. Their social interactions with others do not need to be directed towards acquiring knowledge of language functions and social interaction – except in so far as these vary from one language to another.

Chomsky's theory of Universal Grammar (UG) has primarily been concerned with the acquisition of syntax. It denies the premise of the other two L1 theories that language arises from social contact by claiming that virtually all children learn human language regardless of their situations or the ways their parents talk. However much a theory of mind may be needed for social interaction, it is incidental to the acquisition of syntax. None of the modifications to speech or interaction of L1 parents can be shown to be necessary to language acquisition, even if they may provide a small assistance. However diverse the cultural pattern of interaction, children always manage to learn language; the dialogues with babies so often commended in Western societies are not found in many societies, say Samoa (Ochs & Schieffelin, 1984). All you need to learn a first language acquisition is a normal human mind and exposure to language.

Chomskyan theory sees language acquisition as the child's language faculty creating language knowledge by reacting to language input. The child possesses inbuilt principles and parameters that are applied differently according to the properties of the lexical items the child learns. A lexical item like faint projects particular properties on to the sentence – it can't have an object, he fainted her, or an inanimate subject, the house fainted, its subject comes before it, i.e. he fainted, not after, fainted he, and so on. Acquisition means acquiring the properties of thousands of lexical items like faint. Chomsky's recent Minimalist Program (MP) (Chomsky, 1995) divides the language faculty into the broad faculty of language (FLB) and the narrow faculty of language (FLN); the FLN includes only the property of recursion (embedding a structure within an example of the same structure) (Hauser et al., 2002), thus considerably reducing the innate language structure of the human mind. However most work in developmental linguistics tends to use the earlier Government and Binding theory (Chomsky, 1981), as shown in Guasti (2002), with the exception of a few mainstream syntacticians working in first language acquisition, such as Rizzi (2004). Chomsky's theory remains a theory of knowledge of language to which both social relationships and general cognition are incidental.

The overall UG theory has led to so-called generative SLA research, a subfield with its own articles, conferences and journals, much concerned with the relationship between L1 and L2 acquisition. One controversy is whether L2 differs from L1 acquisition because the L2 learner can no longer use the resources of UG in their minds . The initial debate concerned whether the L2 learner had 'access' to Universal Grammar; perhaps L2 learning differs from L1 acquisition because L2 learners can no longer apply the original principles of Universal Grammar in their minds or perhaps they use them differently. Mostly the answer seemed to be that L2 learners are still capable of learning aspects of language such as structure-dependency without sufficient evidence, just as native children do (Cook, 2003a); hence there is exactly the same evidence for UG in their minds as there is for its existence in the monolingual child's.

The 1990s generativists debated a number of 'hypotheses' about access to UG in second language acquisition including: Full Access, Full Transfer/Full Access and variations on partial access such as Minimal Trees, Valueless Features and Failed Functional Features, all attempts to pin out the syntactic configurations that may be available to the L2 learner. These hypothesis wars are detailed in Cook and Newson (2007) who conclude 'Rather than using the richness of the Universal Grammar theory, this area seems to have become the kind of discussion associated with the question, probably spuriously attributed to St Aquinas, of how many angels can dance on the head of a pin' (Cook & Newson, 2007, 239).

Generative SLA research has taken the current Minimalist Program more seriously than L1 acquisition research. For example SLA research has started to explore the 'interface conditions' where the syntactic core of language impacts upon the actual production of language on the one hand and the cognitive systems of the rest of the human mind (Sorace, 2004).

In general, recent SLA research has drawn on L1 acquisition theories more for its own ends than to test the relationship between L1 and L2 acquisition. In particular it has not paid much attention to the massive descriptive work on L1 acquisition reflected in books such as Bloom (2002), Clark (2003), and O'Grady (2005), which describe the many developmental studies of the past decade rather than sticking exclusively to a particular acquisition theory.

3 differences and similarities between first and second language acquisition

Some of the differences between first language and L2 acquisition are intrinsic and cannot be avoided; some are, so to speak, accidental in that they vary according to the circumstances in which L2 acquisition takes place, in particular inside or outside a classroom. In the vast majority of cases for instance L2 learners are older than L1 children; age inevitably brings with it a host of factors that have little to do with language acquisition itself. The discussion here excludes early childhood simultaneous bilingualism, considering this as 'bilingualism as a first language' (Swain, 1972), i.e. a separate process in which first and second languages are not consecutive.

It may seem to be labouring the obvious to say that the L1 child only knows a single language – that's what first language acquisition means. L2 learners already have at least one other language in their minds; the initial language state of their minds is in principle different from the L1 child because of the first language they already know, however variously this may be interpreted.

This is implicitly denied if the acquisition of the second language is treated in complete isolation from the already present first language, as if L2 acquisition were merely a form of L1 acquisition undertaken later in life. This view has chiefly come from language teachers rather than SLA researchers. Since the Reform Movement of the nineteenth century (Howatt, 2004), mainstream teaching has advocated using the first language in the classroom as much as possible; 'The natural use of the target language for virtually all communication is a sure sign of a good modern language course' (DES, 1990, 58). The argument is effectively that, since the L1 child cannot fall back on another language, neither should the L2 student.

The unique selling point of SLA research is the relationship between two languages in the same mind, leading to the vast area of transfer, whether from L1 to L2, L2 to L1 (reverse transfer) or one L2 to another L2 (lateral transfer) (Jarvis & Pavlenko, 2007). L2 acquisition necessarily differs from L1 acquisition because everything the learner acquires and does potentially involves both first and second languages. Weinreich (1953) suggested that two of the forms bilingualism may take are coordinate bilingualism in which the languages are effectively kept in separate compartments and compound bilingualism in which they are in contact. The integrative continuum (Cook, 2003b) sees a continuum from total separation to total integration of the two languages rather than discrete compartments; the point on the continuum varies for individual L2 learners, for different aspects of language and for different situations. That is to say, the L1/L2 mental relationship has many variations and cannot be stated in simple terms even for a particular individual, whose L1 and L2 vocabulary say may be closely linked, but whose L1 and L2 phonologies may be quite distinct. One doubts whether any L2 learner is actually at the extreme compound and coordinate poles of the continuum, given the persuasive evidence for influence of the second language on the first described in Cook (2003b).

L1 acquisition has seen continual controversy over the links between language development and social and cognitive development. At one extreme UG theorists attempt to isolate language from other cognitive systems; they go as far as the conceptual-intentional interface between the computational system of language and the rest of the mind but stop there (Chomsky, 2000). To them the controversy concerns maturity of the language faculty itself, whether it is essentially the same from birth, just requiring language experience or exposure – the Gradual Development Hypothesis Deprez, 1994) – or whether the faculty itself matures – the Full Competence Hypothesis (Poeppel & Wexler, 1993). The relationship of L1 and L2 acquisition in Universal Grammar theory depends on whether the same Universal Grammar is present in the mind of the L2 learner as the native child or it has matured into some other form.

At the opposite extreme, language development has been directly tied into cognitive development. Piagetians have often traced particular aspects of language development back to cognition: the one-word stage depends for example on the sensorimotor abilities of object constancy and representational thinking; complex syntax requires the ability to conserve at the concrete operations stage (Sinclair de Zwart, 1969). Rick Cromer claimed that where there was a link between language and cognition, language depended on cognition (Cromer, 1974). The development of spatial concepts goes hand in hand with the development of L1 spatial terms, even if sorting out cause and effect is still uncertain (Bloom, 2005).

Nor can it be coincidence that the child's development of vocabulary goes along with the expansion in the child's short-term phonological memory (Gathercole and Baddeley, 1993). Social development too develops over the years the child is acquiring language. Children who first attend playgroup for instance prefer to speak to adults rather than to the other children present; they slowly develop the ability to talk to their peers (Cook, 1979). Similarly they start with a poor awareness of how to switch speaking style; young children have no idea of when to whisper, often to the embarrassment of their parents (Weeks, 1971). In many areas of L1 acquisition research, it is necessary to investigate the connection between language development and other aspects of development, even if it eventually proves that the barrier between language and the rest of the mind in the UG theory is true.

L2 learners start from the position of having done all of this once already. They are older and more mature than the L1 child and so have whatever advantages that age confers in terms of working memory, conceptual and social development, command of speech styles, and so on. The L2 learner does not start from the L1 tabula rasa of knowing nothing about language (apart from the built-in paraphernalia of Universal Grammar). More specifically, once a child has learnt how to mean, they are no longer the same person and cannot regress to a point where they no longer know how to mean: language itself is there for the L2 learner, even if the specific second language is not.

Much maturation is then transformation. In Gleitman's terms, frogs do not go back to being tadpoles when they learn a second language. The aspects of language acquisition that are related to maturation are not reversible; the L2 learner starts with the attributes of maturation appropriate to their age, not those of the L1 child, whether emotional, conceptual, or any other changes that growing up entails. Maturation is seldom a matter of either/or sudden change but a continuous process. One of the variables in L2 learning is that the L2 learner may be at any point on this developmental continuum, ranging say from a nearly adult-like short term memory to a nearly child-like memory and may be at any stage of Piagetian development from the infant's sensorimotor to the adult formal operational. L1 children acquiring language are in step with normal development; L2 learners are out of step, to a greater or lesser degree – an extreme form of décalage between stages in Piagetian theory (Piaget & Inhelder, 1969).

A major factor in many L2 learners' lives is literacy. Learning to read and write changes people's thinking (Luria, 1976) and brain structures (Petersen et al, 2000). Most SLA research is, however, about literate L2 learners who have been transformed by literacy, as Bialystok (2007) points out. Indeed specific types of writing system have overall effects on people's thinking (Cook & Bassetti, 2005): Japanese children remember geometrical patterns better than English children (Mann, 1986) because their writing system is more visually than phonologically based. English readers place images of events such as breakfast, going to school, going to bed etc in a left-to-right order, while Hebrew and Arabic readers use right-to-left order, showing the directionality in the respective writing systems (Tversky et al, 1991).

Incidentally this undermines the view that L2 teaching should start with the spoken language; as Harmer (1998, 53) puts it, 'Because many people acquire languages by hearing them first, many teachers prefer to expose students to the spoken form first'. The reliance on spoken language is still very much at the heart of language teaching methods, which assume implicitly that speaking comes first and use writing as a prop for written tasks rather than as the main focus (Cook, 2005). Literate adults rely on writing in all sorts of ways and organise their thinking differently.

Age has often been blamed for alleged deficiencies in L2 acquisition. L2 learners are typically older than children acquiring their first language. Perhaps there is a point of no return beyond which the second language can no longer be learnt in the same way or with the same efficiency as you learnt your first language. This is not the place to explore the vast literature on age differences as it is dealt with elsewhere in this volume. It might be for example that your Universal Grammar quota was used up with nothing available for second language acquisition. So your second language would have to be learnt in some way that did not involve Universal Grammar, as argued by say Clahsen and Muysken (1989). However it is not age per se that shuts the door but maturation on a particular scale: it's not being 30 that prevents you learning a new language but having the memory system, the cognitive abilities and the social situations etc of a 30-year-old. The variable is not age itself but one of the inevitable companions of age.

The vast majority of children acquire their first language in a primal family care-taking situation; the situations of human babies are rather similar apart from cultural differences in child-rearing practices. Virtually all human children learn human language; nothing stops a child learning their first language other than the total absence of language. First language learning can be taken for granted: it's what human beings do to be human.

L2 learners, however, encounter the second language in a variety of situations, ranging from Palestinian prisoners in Israeli jails learning Hebrew to teenagers in the USA learning Chinese as a heritage language, from Vietnamese and Poles learning Italian in Toronto for their workplaces (Norton, 2000) to footballers learning English to play in the English Championship League (Kellerman et al, 2005), and from Japanese children learning Spanish at school to married couples bridging the gap between their different first languages (Piller, 2002). Cook (t.a. [2009]) itemises some of these L2 user groups as: people using an L2 within a larger community, people using an L2 internationally for specific functions, people using an L2 globally for a wide range of functions, people historically from a particular community (re-)acquiring its language as an L2, and people using an L2 with spouses, siblings or friends. Not to mention those learning the second language in schools because it's a set subject on the curriculum.

One overall group of L2 situations can be called natural, i.e. picking the language up through encounters at work etc. Another group are artificial, i.e. learning it through instruction of one kind or another. In either case the people the learners speak to are not necessarily making concessions to their lower language knowledge, and are certainly not in charge of their lives in the way that an adult is in charge of a child. The perpetual dilemma for language teaching is whether it should deliberately stress the artificial in the classroom or should try and make it as natural as possible, captured in Krashen's well-known distinction between learning and acquisition (Krashen, 1985).

Those who acquire a second language 'artificially' in a classroom may be exposed to teaching methods ranging from grammar-translation to task-based learning by teachers who may or may not be native speakers. Teaching practices vary round the world far more than child-rearing practices and they change rapidly according to the changing winds of language teaching. Neither the natural nor the artificial L2 situations come in a standard package, as L1 situations usually do.

Children barely differ in their acquisition of the first language so far as the main features of the spoken language are concerned. They all end up learning the phonology, vocabulary and grammar appropriate for their dialect, class, age, gender, etc. Individual differences in second language acquisition, however, are extreme. You can't learn a second language, apparently, without having the right motivation, attitude, learning style, learning strategies, cognitive style, personality and all the other factors enumerated in books like Skehan (1989) and Dornyei (2006), mostly concerned with artificial classroom learning. The majority of L2 students give up before they pass the threshold when the L2 becomes genuinely useful to them; allegedly 80% of all students of English in the world are beginners, implying only a small proportion go on to higher levels. Success in L2 learning is a matter of individual variation; success in L1 acquisition is not.

The language input that L1 children get from their caretakers differs dramatically from that provided to the L2 learner. In natural contact situations, the input is closest to that in L1 acquisition. Parents simplify what they say to children and how they interact with them, using what Bruner (1983) calls the LASS (Language Acquisition Support System); native speakers speaking to non-natives simplify their speech in ways known as foreigner talk but hardly simplify topics in the same way parents do to children (Freed, 1980). In the artificial teaching situation, coursebooks and language teachers simplify the language in various ways, say the vocabulary limits put on graded readers (Nation, t.a.). Practical language teaching is almost inconceivable without simplified language; approaches using authentic uncensored materials have usually either been used at a late stage or have used tiny amounts of speech (Cook, 2008 [New edition 2016]). The Interaction Hypothesis has however maintained since 1981 that what is necessary is simplified interaction, not simplified language (Long, 1981; 1996), undeterred by the lack of proof for its necessity in L1 acquisition.

Second language teaching has often attempted to recreate the conditions of the L1 child in the L2 classroom mostly in terms of using only a single language and having a simple interaction between students and teachers or between students. The Interaction Approach holds recasts to be important for L2 acquisition (Long, 1996). The Sociocultural Model too argues that, since L1 acquisition depends on bridging the ZPD gap between what the child can do unaided and what they can achieve with the help of others through 'scaffolding', then so should L2 acquisition (Lantolf, 2000). But, however vital ZPD may be to an L1 child, scaffolding may function differently for an L2 learner in a different situation at a different developmental level.

The crucial difference between first and second language acquisition according to many is the success of first language acquisition versus the failure of second language acquisition, summed up by Bley-Vroman (1989):

'The lack of general guaranteed success is the most striking characteristic of adult foreign language learning. Normal children inevitably achieve perfect mastery of the language; adult foreign language learners do not… one has the impression of ineluctable success on the one hand and ineluctable failure on the other' (Bley-Vroman, 1989, 42-44)

Undoubtedly this view has been shared by the majority of SLA researchers. Ellis (1994, 107) summarised nine differences between L1 acquisition and L2 acquisition, using Bley-Vroman (1988):

The task of SLA research is then taken to be explaining why L2 acquisition is unsuccessful in comparison to L1 acquisition; 'why, in general, adults fail to achieve full native-speaker competence' (Felix, 1987, 144). If an L1 child can master a language in a few years, why can an L2 learner not do the same over many years?

The explanations for this lack of success have drawn on many of the ideas presented earlier. Some are to do with the transformative power of maturation: L2 learners are intrinsically not the same people as young monolingual children.

* Universal Grammar may not be available in second language acquisition (Clahsen & Muysken 1986)

* adults are in the formal operational stage of Piagetian development, which is a handicap to language acquisition (Tremaine, 1975)

In a sense nothing can be done about these immutable differences between L1 and L2 learning, if they exist and are indeed language-related.

* the concentration on the here and now in conversations with children is lost in adult conversation (Hatch, 1978)

* adults are more likely to be learning in formal classrooms that are less conducive for natural acquisition Krashen, 1985)

These are in principle changeable; we could treat L2 learner like L1 children linguistically and socially, reducing them to child-like dependence etc. The most extreme suggestion from McNeill (1965) was that L2 learners should memorise the two-word sentences of young L1 children like more up, to provide them with the 'deep structure' missing in L2 learning.

However the issue of success is a red herring. The child is learning their first language and has no other: the L2 learner is learning a second language when they already have a first. Why should mastery of a second language be measured against the mastery of a first? L2 learners are only failures if they are measured against something they are not and never can be – monolingual native speakers. Does an apple make a good pear? A classic disproof of this was the Bitch 100 test, which proved white Americans were failures at speaking Black American English (Williams, 1975); my own Can you talk Black? test attempts to make the same point (Cook, t.a.). Clearly, if we test monolingual native speakers on knowledge of a second language they would score zero. The success of L2 users is not necessarily the same as that of monolingual native speakers; they are doing different things with language with different people and have a range of other abilities for code-switching and translation no monolingual native speaker can match. To call what the vast majority of L2 users achieve failure is to accept that the only valid view of the world is that of the monolingual: knowing only one language is normal, knowing two is unusual. Only in a monolingual universe is a multi-competent person a failure for not speaking like a monolingual.

The lack of success has haunted the discussion of L1 and L2 acquisition. If you expect L2 knowledge and processing to be identical to that of a monolingual speaker of the language, you're going to be disappointed. The L2 user has a more complex overall language system that includes two languages; neither the first nor the first language in a bilingual are isomorphic with the first language in a multilingual of either language. In recent years researchers have made a nod in the direction of abandoning the monolingual native speaker as the model of second language acquisition – and then go on to use a research methodology which precisely compares the L2 user with native speakers to their disadvantage – grammaticality judgments, obligatory occurrences, and the rest.

So, whatever the differences between L2 learners and L1 children, they are not a matter of success but of difference. L2 users are successful with regard to L2 use, not L1 use. The measurement of success is relative to the goal, not absolute. The rationale for comparing them with the monolingual native speaker is convenience; as we saw at the beginning, L1 acquisition research has a range of discoveries and techniques that SLA research can draw on. But, unless used carefully, they only measure L1 success, not L2 success. Many L2 learners indeed 'fail' to reach successful levels of L2 use but this has little to do with the levels reached by monolingual native speakers. If there are indeed differences between L1 and L2 acquisition, relying on L1 measures of success for L2 users will prevent any unique features of L2 acquisition such as differences in metalinguistic ability (Bialystok, 1993) or cognition (Cook et al, 2006) from manifesting themselves and categorise any differences as failure.

To sum up, the discussion has presented the main points that have been raised over the relationship between L1 and L2 acquisition. The relationship has been symbiotic for SLA research in terms of underlying theories and of specific research techniques. It has been largely one-way in that L1 acquisition research does not seem to have been influenced by SLA research. The relationship is not simple and has to handled with caution, avoiding over-simplistic claims; in some respects the two processes are similar, in some respects different, and this depends partly upon factors that are nothing to do with acquisition per se. There are many ways of understanding L1 acquisition with no single unifying model, even more ways of looking at L2 acquisition. Arbitrarily deciding on one L1 theory, say generative L1 acquisition, or picking out one L1 acquisition factor, say SOV word order, hardly allows one to assert L2 learning is fundamentally different from L1 acquisition, as in say Clahsen and Muyskens (1986).

We have also hinted throughout that it may not be a proper question to ask if L2 acquisition is like L1 acquisition. Like has to be compared with like; if the processes were quite different, this would not be revealed by measuring one of the processes by the standard of the other. There are pear-shaped apples called Worcester Pearmains but this says little about apples as a fruit, just some of their non-prototypical forms. L1 acquisition theory and L1 acquisition research methods are a convenient source that SLA research can borrow from, just as Teflon frying pans were allegedly a spin-off from the NASA space program. They are a source of ideas for looking at L2 acquisition itself, like ideas borrowed from reading research or from connectionism, and so on. Using them does not force SLA research into a junior role in the research; they're being used for different purposes.

The danger lurking beneath the surface is the assumption that there is only true form of language knowledge, the native speaker's, and only one true form of language acquisition, first language acquisition. If exploiting the relationship goes beyond borrowing methods, the ideas of L1 acquisition confine SLA research and inevitably leas to the diminution of L2 acquisition to a pale imitation of L1 acquisition. If one accepts the multi-competence hypothesis that knowing and using two languages is a distinct state of human minds, the L1/L2 comparison becomes problematic: L2 acquisition is necessarily different because it involves the constant presence of a second language in the same mind as a first.

Going beyond this comes the argument that the overall theory of language acquisition has to accommodate the human potential for learning more than one language from the outset, not as a footnote to the acquisition of the first language (Cook, t.a.; Satterfield, 2003). Looked at through the looking-glass of multi-competence, language acquisition is acquiring two or more languages; monolingual first language acquisition is a historical accident that stops the child reaching the normal human multi-competence state. The monolingual native speaker is language-deprived; they would have acquired multi-competence in more than one language if their caretakers had not deprived them of a second language, a standard Chomskyan argument about the environment translated to second language acquisition (Cook, t.a).

The same applies to the relationship of the L1 and L2 communities (Cook, t.a.), which we have not tackled here. SLA and bilingualism research have assumed a dominant L1 community; the L2 user petitions to belong to another community: 'An individual's use of two languages supposes the existence of two different language communities; it does not suppose the existence of a bilingual community' (Mackey, 1972, 554). Many parts of the world like India and Central Africa are, however, genuinely multilingual communities where languages function alongside each other in diverse roles; it is meaningless to say that the L2 user joins a monolingual community as an outsider rather than belonging to a community that uses many languages, called 'the multi-competence of the community' by Brutt-Griffler (2002). The comparison of L1 and L2 in the community may be interesting but it may conceal the distinctive nature of the truly multilingual community.

One sub-theme here has been language teaching. Most language teaching methods have pre-judged the relationship of L2 to L1 acquisition by assuming that 'natural' L1 acquisition is the basis for all acquisition, however much they differ in what they understand by 'natural'. For example Total Physical Response 'simulates at a speeded up pace the stages an infant experiences in acquiring its first language' (Asher, 1986, 17). From the Direct Method to Task-based Learning, language teaching has insisted on a mock target language situation, in which the first language plays no part. Students are required to speak the second language from the moment they step inside the classroom and should not be allowed to revert to the first language; the teacher should make the classroom a monolingual target language situation, not a bilingual situation. While the first language necessarily exists in the L2 learner's mind, the accepted view is that it should be forcibly prevented from appearing in the classroom. The implications of the multi-competence approach for language teaching have been spelled out elsewhere in general (Cook, 2007). But, to take a more neutral position, one should at least say that teachers should be wary of accepting advice about language teaching goals and methods based on the comparison of L1 and L2 learning rather than on the independent study of second language acquisition.

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