Interlanguage

Definition:

Interlanguage is the internally consistent, evolving linguistic system that a second language learner constructs and uses at any given point during the acquisition process. It is neither the learner’s first language (L1) nor a faulty approximation of the target language (L2) — it is a distinct, rule-governed system in its own right. The learner’s interlanguage contains unique forms, rules, and structures that may not exist in either the L1 or the L2, and it evolves systematically over time as the learner acquires new input and revises their internal grammar. The concept was introduced by Larry Selinker in 1972 and fundamentally changed how SLA researchers and language teachers understand learner errors.

Also known as: Learner language, approximative system, transitional competence

In-Depth Explanation

Before interlanguage: contrastive analysis and error analysis.

Prior to Selinker’s formulation, second language learning was dominated by contrastive analysis — the hypothesis that difficulty in L2 learning is directly predictable from structural differences between L1 and L2. Errors were viewed as interferences from the L1 and were to be minimized through pattern drills and error correction. A learner’s non-target-like utterances were simply “mistakes” — failures to perform correctly.

Error analysis in the late 1960s (Corder, 1967) began to challenge this view: many learner errors could not be attributed to L1 interference but appeared to be developmental — systematic errors also made by learners with different L1s, suggesting they reflected internal cognitive processes rather than cross-linguistic transfer.

Selinker synthesized these observations and proposed a fundamentally different frame: learner language is a system, not a set of errors with reference to a target. The learner is constructing a grammar, not failing at a grammar.

Properties of interlanguage.

Systematicity: Interlanguage is rule-governed. Learners apply consistent rules — even if those rules differ from target-language rules. A learner who consistently applies a wrong rule is demonstrating a grammar, not random errors.

Dynamism: Interlanguage evolves over time. As learners receive new input, encounter feedback, and engage in practice, they revise their internal rules and their interlanguage progresses toward the L2 target (though not always linearly).

Permeability: Interlanguage rules can be revised — unlike a fully acquired native language system, which is largely fixed. This permeability is what makes learning possible.

Transfer: Elements from the L1 are incorporated into interlanguage — phonological, lexical, syntactic. This transfer is not merely “interference” but a strategy the learner uses when their current interlanguage does not have resources to handle a communicative demand.

Simplification: Learners often adopt simplified rules that cover many cases rather than the full complexity of target-language rules. “Overgeneralization” (applying a rule beyond its proper scope — e.g., “I goed” for “I went”) is a form of simplification that reveals the learner’s internalized grammatical rule.

Fossilization (potential): Under some conditions, interlanguage development can stop before reaching native-like competence. Certain non-target forms become stable and persistent despite further input and instruction — a process Selinker called fossilization. This is one reason many adult learners plateau before achieving native-like fluency.

Interlanguage and SLA theory.

The interlanguage concept has implications for every major theory in SLA:

For Krashen, interlanguage is the learner’s current state of their acquired system — what has been unconsciously internalized through comprehensible input. Instruction adds to the learned monitor but the acquired interlanguage develops from meaningful input.
For interaction theorists (Long), interactions provide feedback that specifically targets interlanguage features causing communication problems, driving revision of the internal system.
For Swain, forced production reveals gaps in the interlanguage and pushes learners to notice and address them.

Interlanguage and Japanese.

Japanese presents rich interlanguage phenomena for English-speaking learners:

Phonological interlanguage: English speakers often transfer English phoneme categories to Japanese, producing non-native pitch accent, vowel length distinctions, and consonant sounds. The geminate consonant system (long consonants in words like “kitte” vs. “kite”) is a frequent interlanguage challenge — English interlanguage typically simplifies the distinction.
Particle interlanguage: Japanese particle usage (?, ?, ?, ?, ?…) follows complex rules with no English equivalent. Learner interlanguage for particles typically involves simplification — overuse of ? as a default topic/subject marker — before full native-like discrimination is achieved.
Verb-final syntax: English-speaking learners must restructure their interlanguage at a deep syntactic level (SOV word order, verb-final sentences, pre-nominal modifiers) rather than simple lexical substitution.

Interlanguage in SRS contexts.

Understanding interlanguage explains why SRS alone does not guarantee acquisition of complex grammar: SRS efficiently builds declarative knowledge (vocabulary items, facts) but does not automatically trigger revision of implicit interlanguage rules. Interlanguage revision requires noticing a gap between current production and target forms — which typically happens through meaningful interaction, focused input, or pushed output rather than repeated flashcard review. Effective language study combines SRS (for vocabulary and formulaic chunks) with communicative practice (which stresses and develops the interlanguage).

Common Misconceptions

“Interlanguage errors are just mistakes to be corrected.”

Interlanguage errors are data revealing the structure of the learner’s current internal grammar. Systematic errors in a learner’s output are evidence that they have internalized a rule — the wrong rule, perhaps, but a rule nonetheless. Effective feedback targets the rule, not just the surface error instance.

“A good learner has less interlanguage.”

Every learner has an interlanguage at every stage below native-like proficiency. Having an interlanguage is not a failure state — it is the acquisition process. The goal is an evolving, progressing interlanguage, not the absence of one.

“Native speakers don’t have interlanguage.”

Interlanguage is a learner language concept. Native speakers have fully acquired L1 grammars, which are by definition not interlanguages. However, native speakers learning L2s have interlanguages just like any other learner — and L1 transfer appears in their systems just as in anyone else’s.

History

1967: S. Pit Corder publishes “The significance of learners’ errors” (IRAL), arguing that learner errors are systematic, not random, and reflect the learner’s current knowledge state. This reframes errors as evidence of internal grammar rather than performance failures, laying groundwork for interlanguage theory.

1971: William Nemser publishes “Approximative systems of foreign language learners” (IRAL), independently developing a similar concept — the “approximative system” — that a learner uses as a transitional system en route to full L2 acquisition.

1972: Larry Selinker publishes “Interlanguage” (IRAL) — the paper that names and formally defines the concept. Selinker describes five central processes operating on interlanguage: language transfer, transfer of training, strategies of second language learning, strategies of second language communication, and overgeneralization of target language rules. He also introduces the concept of fossilization.

1970s–1980s: The interlanguage framework generates large research programs studying learner error systematicity, developmental sequences, L1 effects, and acquisition orders across different L2s. The “morpheme order studies” (Dulay & Burt; Bailey, Madden & Krashen) show consistent developmental sequences for acquiring English morphemes, supporting the interlanguage view that acquisition follows internal cognitive schedules.

Present: Interlanguage is the default framework for describing learner language in SLA research. Despite the replacement of some Selinker-era specific claims (e.g., the five processes) with more sophisticated models, the core concept of learner language as a systematic, evolving internal grammar remains foundational.

Criticisms

The interlanguage concept has been criticized for implying more systematicity and regularity than actual learner language data typically shows — real L2 learner production is highly variable, with the same learner producing both target-like and non-target-like variants of the same form within a single text or conversation. Variability researchers argue that this variability is not noise around a systematic interlanguage but is itself systematic (conditioned by task type, attention to form, discourse context), challenging the psycholinguistic reality of a stable interlanguage grammar. The term has also been questioned for implying that the goal is convergence toward the native speaker norm — a progressive “movement toward” the target language — rather than recognizing developmental paths that may diverge from native-speaker norms permanently.

Social Media Sentiment

Interlanguage is one of the most frequently referenced SLA concepts in language learning communities — the insight that learners have their own systematic grammar at each stage of development (not merely a deficient version of the target language) is widely used to interpret learner errors constructively rather than as simple mistakes. The idea that errors are evidence of active hypotheses about the L2 (not random failures) is a community-friendly reframing of error that reduces anxiety. Fossilization — the stabilization of interlanguage at a stage short of full target-language competence — is a common community discussion topic related to interlanguage theory.

Last updated: 2026-04

Practical Application

Understanding interlanguage means interpreting your current L2 production not as “bad target language” but as a systematic grammar at your current development stage — and using error patterns as diagnostic information about which rules you’ve overgeneralized or which form-function mappings you haven’t yet acquired. Deliberate attention to forms where your interlanguage diverges from the target (common learner error patterns for your L1-L2 pair) is more efficient than general practice.

Related Terms

Research

Selinker, L. (1972). Interlanguage. International Review of Applied Linguistics in Language Teaching, 10(3), 209–231.
Summary: The foundational paper introducing interlanguage as a theoretical construct. Selinker describes the learner’s developing language system as neither L1 nor L2 but a distinct rule-governed system shaped by five central processes: language transfer, transfer of training, strategies of L2 learning, strategies of L2 communication, and overgeneralization. Also introduces fossilization. One of the most cited papers in SLA research.

Corder, S.P. (1967). The significance of learners’ errors. International Review of Applied Linguistics, 5(4), 161–170.
Summary: The precursor paper to Selinker’s interlanguage theory. Corder argues that learner errors are systematic rather than random and reveal the learner’s current internalized grammar — calling this the learner’s “idiosyncratic dialect” and treating errors as meaningful data about the acquisition process rather than performance failures to be eliminated.

Selinker, L. (1992). Rediscovering Interlanguage. London: Longman.
Summary: Selinker’s own comprehensive retrospective and expansion of the interlanguage framework, incorporating two decades of subsequent research and addressing critiques. Updates the original conception with developments in SLA theory.

Ellis, R. (1994). The Study of Second Language Acquisition. Oxford: Oxford University Press.
Summary: The most comprehensive single-volume treatment of SLA theory, dedicating substantial sections to interlanguage and its development. Covers acquisition orders, developmental sequences, variability in interlanguage, and the role of instruction in modifying learner grammar.

Tarone, E. (1983). On the variability of interlanguage systems. Applied Linguistics, 4(2), 142–163.
Summary: Addresses variability in interlanguage — the observation that learners use different forms in different contexts (formal vs. informal, careful vs. unmonitored speech). Tarone argues for a style-shifting model in which the learner’s interlanguage system encompasses a range of forms rather than a single uniform grammar, adding nuance to the systematicity claim.