INTERLANGUAGE

Introduction and Core Definition

Interlanguage is a fundamental concept within the fields of linguistics and second language acquisition (SLA), representing the unique and dynamic linguistic system constructed by a learner who is in the process of mastering a target language (L2). This term describes the transitional, often idiosyncratic, state between the learner’s native language (L1) and the desired proficiency in the L2. Crucially, interlanguage is not merely a collection of errors or a deficient version of the target language; rather, it is a coherent, rule-governed system in its own right, reflecting the learner’s current hypotheses about how the L2 operates. It is an evolving grammar, lexicon, and phonology that the learner employs for communicative purposes, even if it deviates significantly from the standard native-speaker norm. The study of interlanguage allows researchers to move beyond simple error analysis to understand the cognitive processes and systematic developmental stages inherent in non-native language learning, emphasizing the learner’s active role as a constructor of linguistic knowledge.

The core characteristic defining interlanguage is its hybrid nature. It functions as an intermediate linguistic structure, integrating elements drawn from both the source language (L1) and the target language (L2), alongside unique features generated creatively by the learner. This blending results in structures that might be entirely foreign to both native speakers of the L1 and native speakers of the L2. For instance, a learner whose L1 uses postpositions might consistently place prepositions incorrectly in the L2, demonstrating the influence of L1 interference. Concurrently, the learner might also apply an L2 grammatical rule too broadly—such as adding the regular past tense suffix ‘-ed’ to irregular verbs (e.g., “eated”)—illustrating an internal, systematic overgeneralization of L2 rules. Understanding interlanguage involves recognizing that these constructions are not random mistakes but are logical outputs based on the learner’s currently internalized set of linguistic rules, which are systematically revised and refined over time as new input is processed and understood.

Furthermore, interlanguage is inherently psycholinguistic in nature, reflecting the cognitive strategies employed by the learner to manage the complexity of acquiring a new language system. It is a manifestation of the mental grammar under construction, revealing the learner’s ongoing attempts to map meaning onto form, often under conditions of limited knowledge and high communicative pressure. Researchers view interlanguage as a window into the acquisition process itself, providing empirical data on how learners test hypotheses, filter input, and restructure their internal representations of language. This perspective emphasizes that the learning process is neither linear nor strictly additive; rather, it involves complex reorganization, where previously correct forms might temporarily regress as the learner grapples with more complex structures, a phenomenon known as U-shaped development. This constant state of flux underscores the dynamic and non-static quality of the interlanguage system until it potentially stabilizes or reaches a near-native level of proficiency.

Historical Context and Origins

The concept of interlanguage emerged prominently in the late 1960s and early 1970s, marking a significant departure from earlier approaches to second language learning that primarily focused on Contrastive Analysis (CA) and Behaviorism. Prior to the interlanguage hypothesis, CA posited that most learner errors could be predicted based solely on the structural differences between the L1 and L2. Errors that were not attributable to L1 interference were often dismissed as random or performance-related. However, research began to show that many errors were universal across learners from different L1 backgrounds, suggesting systematic, internal cognitive processes at play rather than just external transfer. Researchers like William Nemser coined the term ‘approximative systems’ (1971), paving the way for the formal introduction of the concept.

Larry Selinker formally introduced the term ‘interlanguage’ in a seminal 1972 paper, establishing the interlanguage hypothesis as a major paradigm in SLA research. Selinker defined interlanguage as a unique linguistic competence separate from both the L1 and the L2, positing that this system possesses psychological reality. He argued that the interlanguage system develops through five central cognitive and learning processes: language transfer (L1 influence), transfer of training (influence of instructional materials), strategies of second language learning, strategies of second language communication, and, critically, fossilization. Selinker’s framework provided a powerful theoretical explanation for the widespread observation that adult learners rarely achieve perfect native-like competence, attributing persistent errors not to lack of effort, but to the stabilization of the interlanguage system itself.

Building upon Selinker’s framework, Stephen Krashen further popularized and integrated the interlanguage concept into his influential theories of SLA, particularly the Monitor Model introduced in 1978. Krashen viewed interlanguage as the natural product of subconscious acquisition driven by exposure to comprehensible input (i+1). He argued that the learner constantly uses this transitional system to form and test hypotheses about the target language structure. The historical shift toward the interlanguage paradigm thus represented a cognitive revolution in SLA, fundamentally changing how researchers and educators viewed learner errors—from viewing them as deficits to recognizing them as evidence of the learner’s creative, systematic construction of a new linguistic system, aligning SLA research more closely with developmental psychology and generative linguistics.

Key Characteristics of the System

The interlanguage system is characterized by several intrinsic qualities that distinguish it from both the L1 and the fully realized L2. One of the most salient features is its systematicity. Despite containing forms and structures considered “incorrect” by native speakers, the interlanguage is not chaotic; it operates under its own consistent, albeit evolving, set of rules. For example, if a learner consistently fails to invert the auxiliary verb in question formation (“Why you are leaving?”), this is a systematic feature of their current interlanguage grammar, reflecting a temporary rule they have established based on perceived input patterns. This internal consistency is crucial because it demonstrates that the learner is actively constructing a mental grammar, using input to formulate hypotheses and test them through production. Errors, therefore, are systematic deviations, predictable based on the learner’s current internal rule set.

A second defining characteristic is dynamism or permeability. Interlanguage is inherently unstable and constantly in flux, especially during the early and intermediate stages of acquisition. This dynamism means the system is highly susceptible to modification based on new linguistic input and communicative demands. This state of constant restructuring involves not just adding new rules but also re-evaluating and discarding old, incorrect rules. However, the systematic nature of the interlanguage means that changes often occur across entire classes of structures simultaneously. For instance, the acquisition of a complex aspect marker might trigger a temporary disruption in the usage of simpler markers before the new system stabilizes. This dynamic quality is often nonlinear, and learners may exhibit temporary backsliding—a U-shaped developmental trajectory—as they attempt to integrate complex linguistic features that challenge their existing structural hypotheses.

Finally, interlanguage is fundamentally variability-prone. This variability manifests in two primary ways: internal and external. Internal variability refers to the learner producing different forms for the same linguistic function within a short span of time, even under identical conditions. For example, sometimes the learner might say “He goes there” and other times “He go there,” reflecting uncertainty regarding the correct morphological rule. External variability, conversely, relates to the differences in language use based on the communicative context or interlocutor. A learner might use a more complex, accurate form when consciously monitoring their speech during a formal test (the careful style), but revert to a simpler, error-prone form during rapid, spontaneous conversation (the vernacular style). This contextual dependency highlights the interplay between the learner’s internalized competence and their performance capabilities, confirming that interlanguage is best viewed as a continuum of styles rather than a monolithic linguistic structure.

Processes and Mechanisms Driving Interlanguage

The construction and evolution of interlanguage are driven by several key cognitive and linguistic processes, many of which involve simplifying the complex task of language mastery. One primary mechanism is Language Transfer, which occurs when the learner relies on the structures, rules, or vocabulary of their native language (L1) to produce utterances in the L2. This can result in either positive transfer (where L1 and L2 structures align, aiding acquisition) or, more commonly studied, negative transfer or interference (where L1 structures clash with L2 structures, leading to systematic errors). For example, a learner whose L1 places adjectives after nouns might produce the non-target-like construction “car red” in English, a clear case of negative structural transfer. While transfer is most visible in early stages, its influence can persist throughout the developmental trajectory of the interlanguage, particularly in areas highly divergent between the L1 and L2.

A second crucial mechanism is Overgeneralization. This involves the learner applying a target language rule too broadly or extending it to contexts where it does not apply, often mirroring the systematic errors observed in first language acquisition. Since language acquisition is fundamentally a process of hypothesis testing, the learner often identifies a pattern (e.g., forming the past tense by adding ‘-ed’) and applies it universally, leading to forms like “buyed” or “rided.” This mechanism is highly systematic and demonstrates the learner’s cognitive capacity to infer rules from limited input. Overgeneralization errors are essential diagnostic tools for researchers because they show that the learner has successfully internalized a target language rule, even if they have not yet mastered the exceptions to that rule. These errors are distinct from L1 transfer errors because they are entirely L2-internal, reflecting the learner’s independent construction of L2 rules.

Other significant processes include Simplification and the use of communication strategies. Simplification occurs when the learner reduces the complexity of the target language structure to make production easier, often leading to the omission of function words, auxiliary verbs, or complex syntactic embeddings, resulting in forms that resemble ‘telegraphic speech.’ For example, simplifying complex relative clauses or substituting a single verb form for multiple tenses. Communication strategies, conversely, are conscious attempts by the learner to bridge a gap between their communicative goal and their current linguistic knowledge. These strategies might include paraphrasing, lexical approximation (using a known word for an unknown concept), or appealing for help. While these strategies serve immediate communicative needs and promote fluency, their repeated use can feed back into the interlanguage system, potentially stabilizing or reinforcing non-target-like forms if the learner does not receive appropriate feedback.

The Phenomenon of Fossilization

One of the most complex and debated aspects of interlanguage theory is the concept of fossilization. Introduced by Selinker, fossilization refers to the permanent cessation of learning specific target language features, despite continued exposure to input, practice, and motivation. When fossilization occurs, certain errors or non-target-like structures become permanently entrenched features of the learner’s interlanguage system. This phenomenon is particularly characteristic of adult L2 learners, providing a strong theoretical explanation for the fact that complete, native-like proficiency is rare in post-pubescent acquisition. Fossilization confirms that the development of interlanguage is not always destined for convergence with the target language norm.

The mechanisms underlying fossilization are still subject to extensive investigation, involving a mix of neurobiological, cognitive, and affective factors. Cognitively, fossilization may be related to the permanent establishment of strong neural pathways corresponding to the interlanguage rules, making restructuring extremely difficult once automaticity is achieved—the learner’s system defaults to the L2 structure that has proven communicatively adequate. Affective factors, such such as high levels of Language Ego, low levels of integrative motivation, or perceived social distance from the target language community, have also been implicated, suggesting that the learner may unconsciously stop striving for nativeness. Furthermore, it has been proposed that the systematic use of communication strategies, while effective for fluency, can inadvertently reinforce erroneous forms, making them resistant to change. Once a learner is communicatively successful using a fossilized form, the necessary cognitive pressure to correct it diminishes significantly.

Fossilization is not typically absolute across the entire language system; rather, it tends to affect specific linguistic subsystems. The most common areas for fossilization include phonology (leading to persistent foreign accents, often solidified early in the acquisition process), morphology (e.g., persistent misuse or omission of articles, prepositions, or verbal inflections), or certain challenging syntactic structures (e.g., embedded clauses or complex aspect marking). The pedagogical challenge presented by fossilization is significant, as traditional instruction often proves ineffective against deeply ingrained interlanguage forms. Researchers sometimes differentiate between ‘pure’ fossilization (true cessation of learning) and ‘plateauing’ (a temporary slowing down of development), but the overall consensus is that the interlanguage, for many adult learners, represents a stable, non-native endpoint rather than a temporary stage.

Variability and Stages of Development

The developmental path of interlanguage is often described in terms of identifiable stages, although these stages are highly individualized and rarely strictly linear. Researchers often look for acquisition sequences, particularly concerning grammatical morphemes or the order of negation construction. Studies have shown that learners often acquire certain grammatical features in a relatively invariant order, regardless of their L1 background, suggesting a natural, internally driven sequence of development rooted in cognitive complexity. For example, acquisition research often finds that L2 learners master negation by moving through stages: first using ‘no’ externally (“No understand”), then internally (“I no understand”), and finally mastering the auxiliary verb structure (“I don’t understand”). This sequential consistency provides strong evidence that interlanguage development is guided by universal cognitive constraints related to linguistic complexity and perceptual salience.

Within these developmental stages, variability plays a critical mediating role. Linguistic production is not uniform; learners transition between stages gradually, often exhibiting high degrees of variability at the boundaries of emerging rules. Elaine Tarone (1983) proposed that interlanguage exists as a continuum of styles, ranging from a careful, monitored style used in formal settings to a vernacular, unmonitored style used in casual conversation. The careful style tends to be more target-like because the learner can apply conscious knowledge (Krashen’s Monitor), whereas the vernacular style is considered a purer, more automatic reflection of the acquired, internal interlanguage grammar. This conceptualization views interlanguage not as a single, homogenous entity, but as a set of interacting sub-systems that are activated depending on the situational demands and the attention paid to linguistic form.

Analyzing interlanguage variability helps distinguish between true competence and mere performance fluctuations. If a learner uses a target-like form inconsistently, it suggests the rule is still emerging and has not been fully integrated into the core grammar. Conversely, if a learner consistently produces a non-target-like form across all contexts, that form is likely systematized within the interlanguage. Researchers categorize variability into systematic variability (predictable variation based on linguistic context or social factors) and non-systematic variability (random slips or errors). The movement through developmental stages is characterized by the systematic reduction of non-target-like variability and the stabilization of target-like forms, until the point where the system either reaches near-native competence or stabilizes in a fossilized state.

The Role of Input and Interaction

The development and modification of interlanguage are heavily dependent on the quantity and quality of linguistic input the learner receives, as well as the opportunities for meaningful interaction. According to theories like Krashen’s Input Hypothesis, interlanguage progresses when the learner receives input that is slightly beyond their current level of competence (often termed ‘i+1’). This comprehensible input serves as the data necessary for the learner to test their existing hypotheses and restructure their internal grammar. Without sufficient exposure to target language forms, particularly those that are low in perceptual salience (like grammatical function words), the interlanguage system lacks the necessary evidence to correct overgeneralizations or transfer errors, leading to stagnation or potential fossilization.

Furthermore, interaction plays a crucial role, often mediated through the mechanism of negotiation for meaning. When communication breaks down due to a non-target-like interlanguage utterance, the interlocutors (whether native speakers or other learners) often engage in clarification requests, confirmation checks, or comprehension checks. This conversational negotiation forces the learner to recognize the gap between their intended meaning and the received form, thereby pushing them to modify their output. Theories like Michael Long’s Interaction Hypothesis posit that this negotiated interaction, which highlights structural deficiencies in the interlanguage through immediate feedback, provides optimal conditions for acquisition, converting general input into focused, salient linguistic data that aids in hypothesis revision and eventual rule restructuring.

Interaction not only provides corrective feedback but also offers opportunities for ‘pushed output,’ a concept arguing that learners must sometimes struggle to produce meaningful L2 utterances to move their interlanguage forward. Merrill Swain suggested that producing output compels learners to move from semantic processing (focusing only on meaning) to syntactic processing (focusing on form). When learners are pushed to use structures they have not yet fully mastered, they are forced to retrieve and process linguistic information more deeply, potentially leading to the internalization of new rules or the noticing of gaps in their interlanguage knowledge. Therefore, the interlanguage system is not solely shaped by passive intake; it is actively constructed and refined through a dialectical process involving exposure to rich input and active participation in communicative exchanges that demand continuous self-correction and revision of internalized rules.

Pedagogical Implications of Interlanguage Theory

The interlanguage concept has profoundly influenced Second Language Pedagogy, moving teaching methodologies away from rote memorization and towards communicative approaches that value the learner’s internal, creative contribution to the process. Recognizing interlanguage as a systematic entity means that educators must view learner errors not as failures to be punished, but as valuable evidence of the learner’s current stage of development and the hypotheses they are testing. This perspective shifts the focus from error eradication to error analysis, allowing teachers to diagnose the underlying rule system the learner is currently operating under (e.g., distinguishing between L1 transfer errors and L2 overgeneralization errors) and target instruction accordingly.

A key pedagogical implication is the acceptance of natural developmental sequences. Since acquisition follows inherent cognitive steps (e.g., acquiring negation or relative clauses in fixed orders), instruction should ideally align with these natural routes rather than forcing structures too far ahead of the learner’s developmental readiness. For instance, attempting to enforce the mastery of complex, low-salience grammatical morphemes too early may be futile if the learner’s interlanguage is not yet ready to incorporate them. Effective teaching, therefore, involves providing structured input and interaction that facilitate the natural progression of the interlanguage, ensuring that the target structures are comprehensible and meaningful within the communicative context, rather than relying solely on explicit grammatical explanations.

Furthermore, interlanguage theory informs decisions regarding error correction. Given the systematic nature of interlanguage, correction is most effective when it targets global errors that impede communication significantly, or when it addresses forms that are highly susceptible to modification at the learner’s current stage. Over-correction of errors rooted in deep-seated fossilization or developmentally premature structures often yields little benefit and can be demotivating. Modern communicative teaching often favors implicit corrective feedback—such as recasts (rephrasing the learner’s incorrect utterance correctly) or negotiation for meaning—which exposes the learner to the correct form without disrupting the communicative flow. This approach allows the learner’s internal mechanisms to notice the gap between their interlanguage and the target language, thereby facilitating gradual restructuring and internalization.

Critical Perspectives and Related Theories

While the interlanguage hypothesis remains central to SLA research, it has faced critical scrutiny and spawned several related theories that refine or challenge its original scope. One major critique centers on the vagueness of terms like ‘fossilization’ and ‘systematicity,’ particularly the difficulty in determining when a feature is truly fossilized versus simply being delayed in acquisition. Additionally, some researchers argue that the concept may overemphasize the uniformity of learner processes, potentially neglecting the significant influence of individual differences, socio-cultural factors, and context-specific learning environments, leading to the development of socio-linguistic models of interlanguage variability.

Related theories have emerged to provide more granular models of the interlanguage process. Processability Theory (PT), developed by Manfred Pienemann (1998), focuses specifically on the developmental stages of interlanguage syntax and morphology. PT posits that learners can only process and produce linguistic structures for which they have the necessary cognitive processing mechanisms (e.g., specific placement of grammatical information). This theory provides a highly detailed, predictive model of the acquisition order of grammatical features, essentially mapping the cognitive constraints that dictate the structure of the interlanguage at different points in time. PT thus offers a mechanism that explains why certain interlanguage errors persist and others disappear sequentially, based on the availability of necessary processing resources.

Another theoretical extension involves the integration of Usage-Based theories, which emphasize the role of frequency and pattern recognition in shaping the interlanguage structure. These perspectives suggest that interlanguage structures are built primarily on exposure to highly frequent linguistic patterns (constructions) rather than abstract, innate rules. Errors and non-target forms in the interlanguage might simply represent less frequent, less practiced constructions that have not yet reached automaticity. By integrating insights from cognitive psychology, neurobiology, and linguistic theory, the study of interlanguage continues to evolve, moving toward a more comprehensive understanding of how the human mind manages the complex task of acquiring and maintaining multiple linguistic systems, confirming interlanguage as the indispensable theoretical cornerstone of second language acquisition research.