Three language systems:
1. NL (native language): utterances in the learner’s native language
2. IL (interlanguage): utterances in the foreign language produced by the learner
3. TL (target language): utterances produced by native speakers of the target language
Interlanguage:

In most cases the utterances a second language learner produces are not identical to the utterances a native speaker would have produced in the same situation.

These different utterances in learner language Selinker calls
“interlanguage”.
Fossilization:

Fossilizable structures are items, rules, etc. which second language learners tend to keep in their IL even if they know how it would be correct in the TL.

Examples are well known errors like French learners pronouncing a uvular /r/ in English or the Time-Place order after a verb of German learners.

A lot of these errors seem to be eradicated when the learners advance in learning the language. But the errors often reappear when the learners feel nervous or when they are facing new and difficult things.

Five central processes:
1. Overgeneralization of TL rules:

Double marking of tense: What did he intended to say?

Overgeneralization of the possible combination of verbs with certain nouns: I drive the bicycle.
(use drive with all vehicles)

Overuse of contractions: Max is happier than Sam’s these days.
2. Transfer of training:

Textbooks and teachers often use certain structures or expressions again and again to explain things or in drills.
Learners tend to transfer these structures and expressions into their IL.
Example:

Serbo-Croatian Speakers of English were found to have difficulties with the he/she distinction .

They used he on almost every occasion where either he or she was needed and did not seem to care about gender distinctions.

Reason for this: Textbooks and teacher gave presented their examples and drills almost always with he and never with she
3. Language transfer:
 Items taken over from the learners’ NL into their IL

4. Strategy of second language learning:
One example of strategy is to reduce the TL to a simpler system:

Avoid articles: It was Ø nice, nice trailer, Ø big one

Avoid plural forms: I have many hundred carpenter my own

Avoid pas tense forms: I was in Frankfurt when I fill application
5. Strategy of second language communication:

Although learners might know the correct structures of the
TL they might not (always) care about them very much while having a conversation.

Reason for this: Learners feel that their speech is hesitant and disconnected when they think too much about correct structures while talking. To keep the conversation fluent they accept making mistakes.
Selinker, Larry. “Interlanguage.” Error Analysis. Ed. J.C. Richards. London: Longman,
1978, pp. 31-54