Six Principles of Second Language Development

1. Interlanguage Principle

The interlanguage principle posits that second language learners create their own unique linguistic systemneither their first language nor the target language. This evolving system, called "interlanguage," contains elements from both the native language and the target language, along with invented rules and patterns.

Interlanguage develops over time as learners hypothesize about how the target language works and test these hypotheses through communication. Errors are not merely mistakes to be corrected but evidence of the learner's active construction of the language system. Understanding interlanguage helps educators view "errors" as developmental steps rather than failures, informing more effective teaching approaches that build upon the learner's current stage.

2. Natural Order Principle

Research has shown that learners acquire grammatical structures in a predictable order, regardless of their native language or teaching methods. This natural sequence means certain features of the language are acquired before others, regardless of formal instruction focus.

For example, in English, the "-ing" progressive form is typically acquired before the "-s" third-person singular present tense marker, which comes before possessives and articles. This principle does not imply that teaching sequences are futile, but rather suggests that instruction should align with natural acquisition orders when possible and understand that some structures may require more time and exposure to be internalized.

3. Comprehensible Input Hypothesis

Stephen Krashen's input hypothesis proposes that learners acquire language primarily when exposed to input that is slightly beyond their current level of competencetermed "i+1," where "i" is their current ability. This comprehensible input allows learners to understand messages while encountering new language elements in context.

Input that is too difficult cannot be understood, while input that perfectly matches current proficiency doesn't challenge the learner enough to promote progress. The optimal learning environment provides rich, understandable language through listening, reading, or interaction that contains new elements within accessible context. This principle emphasizes the importance of exposing learners to meaningful language at the right level of complexity.

4. Interaction Hypothesis

Michael Long's interaction hypothesis emphasizes the crucial role of meaningful interaction in second language development. When learners engage in interactions where meaning must be negotiatedthrough clarification requests, confirmation checks, or comprehension checksthey create optimal conditions for language acquisition.

Interaction provides learners with opportunities to notice gaps in their knowledge, receive modified input from conversational partners, and test hypotheses about how the language works. Collaborative tasks that require exchanging information, solving problems, or discussing topics enable this negotiation of meaning, making interaction a powerful catalyst for second language development.

5. Output Hypothesis

Merrill Swain's output hypothesis suggests that producing language (through speaking or writing) is essential for acquisition beyond what input alone can provide. When learners produce language, they must move beyond semantic processing (understanding meaning) to syntactic processing (using correct form).

Output serves three key functions:

• The noticing/triggering function: As learners attempt to express ideas, they notice gaps in their linguistic knowledge.
• The hypothesis-testing function: Using language allows learners to experiment and receive feedback.
• The metalinguistic function: Producing language helps learners reflect on the language system itself.

6. Affective Filter Hypothesis

The affective filter hypothesis recognizes that emotional factors significantly impact language acquisition. High anxiety, low motivation, and low self-confidence create a "filter" that blocks input from reaching the language acquisition mechanism, regardless of how comprehensible the input might be.

Conversely, learners who feel motivated, confident, and relaxed have a low affective filter that allows input to be more effectively processed. This principle underscores the importance of creating positive learning environments where learners feel comfortable taking risks, making mistakes, and engaging with the language without excessive anxiety or fear of failure.