Editing Second-language acquisition (section)

=== Learnability and teachability ===
Learnability has emerged as a theory explaining developmental sequences that crucially depend on learning principles, which are viewed as fundamental mechanisms of interlanguage language acquisition within learnability theory.<ref>{{Cite web|url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/38613/1/Parker%20%281989%29_WP8%281%29.pdf|title=Learnability Theory and the Acquisition of Syntax|last=Parker|first=Kate|date=May 1989|website=University of Hawai'i Working Papers in ESL, Vol. 8, No. 1, pp. 49-78.}}</ref> Some examples of learning principles include the uniqueness principle and the subset principle. The uniqueness principle refers to learners' preference for a one-to-one mapping between form and meaning, while the subset principle posits that learners are conservative in that they begin with the narrowest hypothesis space that is compatible with available data. Both of these principles have been used to explain children's ability to evaluate grammaticality despite the lack of explicit negative evidence. They have also been used to explain errors in SLA, as the creation of supersets could signal over-generalization, causing acceptance or production of ungrammatical sentences.<ref name=":3">{{Cite web |last=Yip |first=Virginia |date=Aug 1990 |title=Interlanguage Ergative Constructions and Learnability |url=https://files.eric.ed.gov/fulltext/ED335903.pdf |website=CUHK Papers in Linguistics, No. 2. p45-68}}</ref>

Pienemann's [[Teachability Hypothesis|teachability hypothesis]] is based on the idea that there is a hierarchy of stages of acquisition and instruction in SLA should be compatible with learners' current acquisitional status.<ref>{{Cite journal|last=Pienemann|first=Manfred|date=1989|title=Is Language Teachable? Psycholinguistic Experiments and Hypotheses|url=https://eric.ed.gov/?id=EJ385570|journal=Applied Linguistics|language=en|volume=10|issue=1|pages=52–79|doi=10.1093/applin/10.1.52|url-access=subscription}}</ref> Recognizing learners' developmental stages is important as it enables teachers to predict and classify learning errors. This hypothesis predicts that L2 acquisition can only be promoted when learners are ready to acquire given items in a natural context. One goal of learnability theory is to figure out which linguistic phenomena are susceptible to fossilization, wherein some L2 learners continue to make errors despite the presence of relevant input.