Teachability Hypothesis

The Teachability Hypothesis, proposed by Manfred Pienemann (1984), states that instruction can only promote second language acquisition when the learner is developmentally ready to acquire the target structure. A structure from stage 4 cannot be taught to a learner who is still at stage 2 — no amount of drilling, correction, or explanation will override the developmental sequence.

Origins

Pienemann's hypothesis grew from psycholinguistic research on German word order acquisition by migrant workers in Germany (Meisel, Clahsen & Pienemann, 1981). The researchers identified a fixed sequence of stages in the acquisition of German word order rules. Pienemann (1984) then tested whether instruction could alter this sequence and found that it could not: learners who received instruction on structures beyond their current stage did not acquire them. A formal statement appeared in Pienemann (1985) and was later elaborated in his 1989 paper "Is language teachable?"

Core Claims

1. Stages cannot be skipped — developmental sequences are fixed and instruction cannot reorder them
2. Instruction is beneficial when targeted one stage ahead — teaching structures at stage n+1 (where the learner is at stage n) can accelerate progress through that stage
3. Premature instruction is not merely useless — it can be counterproductive — it may confuse learners or cause avoidance of the targeted structure

Relationship to Processability Theory

The Teachability Hypothesis was the precursor to Pienemann's more comprehensive Processability Theory (1998), which provides the psycholinguistic explanation for why stages are fixed. Processability Theory argues that each stage requires specific speech processing procedures (e.g., category procedure, phrasal procedure, S-procedure) that must be acquired in a fixed sequence because each builds on the previous one. The Teachability Hypothesis describes the pedagogical implication; Processability Theory supplies the cognitive mechanism.

Connection to Other Hypotheses

The hypothesis shares ground with Krashen's Natural Order Hypothesis — both claim that acquisition follows a predictable order — but differs in a crucial respect. Krashen argued that instruction has no effect on the natural order at all. Pienemann's position is more nuanced: instruction can accelerate development, but only within the constraints of the developmental sequence. This makes the Teachability Hypothesis more useful for teachers, as it does not dismiss instruction but rather constrains its timing.

The concept also connects to Interlanguage theory (Selinker, 1972), since the developmental stages represent successive interlanguage systems that the learner constructs on the way to the target language.

Teaching Implications

• Diagnostic assessment matters — teachers need to identify where learners are in the developmental sequence before selecting instructional targets
• Sequencing syllabuses by developmental readiness, rather than by perceived grammatical simplicity, may produce better outcomes
• Form-Focused Instruction is most effective when it targets structures at the learner's next stage of development
• The hypothesis challenges structural syllabuses that impose an arbitrary grammatical sequence without regard for learner readiness