Interlanguage, and why your Spanish 4 student stopped improving.

Larry Selinker named one of the most useful constructs in second language acquisition in a 1972 paper. The construct is interlanguage. Its consequence is fossilization. Together they explain the student who has been studying for four years and still says no me gusta los gatos.

What interlanguage is

Larry Selinker's 1972 paper (Interlanguage, International Review of Applied Linguistics) proposed that L2 learners do not move along a single track from no Spanish to native Spanish. They build a third system of their own at every point. The system has rules. The rules are influenced by the L1, by the L2 input, by what has been explicitly taught, by what the learner has noticed, and by general cognitive constraints.

The system is not random error. It is structured. A Spanish 2 learner who consistently says el problema as feminine is following a rule of their interlanguage: nouns ending in -a are feminine. The rule is wrong for problema. It is right for most of Spanish. The interlanguage has internal logic, and that logic is what produces the errors.

Selinker's argument changed how the field talked about errors. Before interlanguage, errors were treated as deviations from the target. After interlanguage, errors were treated as evidence of a system in development. The teacher's job is not to eliminate errors. It is to nudge the system toward the target.

The five processes that shape interlanguage

Selinker identified five processes that build the interlanguage system.

1. Language transfer

Rules from the L1 carry over into the L2. The English speaker who says yo soy quince años (instead of yo tengo quince años) is transferring the be-construction from English. The transfer is often invisible to the learner. It feels like the natural way to say the thing.

2. Transfer of training

Rules accidentally created by how we taught. The learner who insists that ir a + infinitive is the only way to express future is following a rule the textbook created. The simple future form was introduced later or not at all. The training has become the rule.

3. Strategies of L2 learning

The learner's general approach to learning the language. Some learners over-rely on memorization. Some rely on inference from context. The strategy shapes which forms get noticed and which get processed.

4. Strategies of L2 communication

How the learner copes when their interlanguage is insufficient. Avoidance (do not use the form you are unsure of). Approximation (use a related word). Code switching. Asking for clarification. Each strategy keeps the conversation moving but freezes the underlying gap.

5. Overgeneralization

The most prolific source of interlanguage rules. The learner notices that -ar verbs in preterite go é, aste, ó, and extends the pattern to verbs that do not work that way. Yo sabé instead of yo supe. The rule is sound. The application is wrong.

The existence of a separate linguistic system based on the observable output which results from a learner's attempted production of a target language norm.

What fossilization is

Selinker's second key claim was that some interlanguage features stop developing. The learner plateaus on those features and never moves past them. This is fossilization. The student who has been studying Spanish for six years and still says no me gusta los gatos instead of no me gustan los gatos has fossilized the gustar agreement.

Fossilization is not the same as a gap. A gap can be filled by exposure and practice. A fossilized form has been exposed to corrective input and instruction many times and still does not move. The form has become part of the interlanguage system.

Han (2004, Fossilization in Adult Second Language Acquisition, Multilingual Matters) is the standard book on the construct. The research base has confirmed that some features in some learners do stop developing even with continued exposure. The mechanism is not fully understood. The phenomenon is widely observed.

Why fossilization is depressing and important

It is depressing because it pushes back against the teacher's assumption that exposure plus instruction eventually fixes everything. Sometimes it does not. A fossilized form will resist correction for years.

It is important because it forces us to prioritize. Not every interlanguage error is fossilizing. Some are developmental and will resolve. Some are stable and will not. The teacher who treats every error as equally urgent misses the ones that are actually about to lock in.

Han identifies risk factors. Late onset of acquisition (consistent with the critical-period article). Low input volume. Reduced motivation. Specific features that lack salience in the input. Forms that have a usable L1 translation that is wrong but communicates. All raise the risk that a developing error will fossilize.

The most common fossilizing features in Spanish for US learners

Gustar agreement

Me gusta for both singular and plural objects. The English transfer (I like + noun) hides the Spanish structure (it pleases me). Once it locks, it is hard to move.

Ser versus estar with adjectives

Especially for state-temporary versus inherent-trait distinctions. Many adult learners settle on a ser-everywhere or estar-everywhere strategy and freeze.

Preterite versus imperfect for non-prototype verbs

The state verbs that flip meaning in preterite (covered in the aspect-hypothesis article). Many learners fossilize the imperfect-only pattern for these verbs.

Gender agreement on -e and consonant-final nouns

The clear -a and -o nouns are usually fine. The harder cases (la calle, el café, la ciudad, el reloj) often fossilize as the wrong gender.

Subjunctive in adverbial clauses

The contingency-based subjunctive (cuando, hasta que, en cuanto with future reference) is one of the latest-to- develop and most-likely-to-fossilize features.

How to push fossilization back

The pure-input camp argues that fossilization is reduced by more input. They are partly right. More input does slow fossilization for developmental forms.

The focus-on-form camp argues that explicit attention is required for the features at highest risk. They are also partly right. The features that fossilize are often the ones that lack salience in input. They need the form focus to get noticed.

The defensible practice is: high input volume to fuel general development, plus deliberate form focus on the specific features at risk for the specific student. The recasts-versus-prompts article covers the corrective feedback move that helps. The processing-instruction article covers the input intervention that helps.

What this means for your Monday

Pull out the errors your Spanish 3 and 4 students made on their last writing assignment. Sort them into two piles: errors I have not yet taught the form for (developmental gaps) and errors I have taught the form for and the students keep making (fossilization risks).

For the developmental pile, plan instruction. For the fossilization pile, plan targeted intervention. Pop-up form focus on the specific feature, prompts instead of recasts when it comes up in conversation, and processing instruction items that force the form-meaning connection the student has been avoiding. Track over the semester. Some forms will move. Some will resist. The diagnosis is the first step.