This chapter introduced the xu-argument as a systematic theory of language learning emphasizing the integration of linguistic and non-linguistic factors to generate alignment effects. It highlighted the tight coupling of comprehension and production, creative imitation combining content creation with language imitation, and the principle of “Learn Together, Use Together” (LTUT), which stresses context-dependent learning and use, particularly through dialogic interactions with native speakers.

This chapter discussed the xu-argument’s relationship with mainstream frameworks such as usage-based theory, complex dynamic systems theory, and sociocultural theory. Unlike these macro-level theories, the xu-argument originated from classroom observations and focuses on language teaching efficiency through the mechanism of alignment triggered by creative imitation. It posits a cognitive ecosystem where the asymmetry between comprehension and production drives language proficiency development via continual reconciliation.

This chapter researched the distinctions between L1 and L2 acquisition within the xu-argument framework, emphasizing L1 transfer as a key differentiator that affects the speed and ease of L2 learning. It argued that successful acquisition in both cases depends on interactive experience facilitated by xu, while factors like age, context, and frequency influence the rate but not the fundamental process. It suggested the xu-argument provides a unified explanatory framework addressing longstanding SLA issues such as learnability and acquisition order.

This chapter described the challenges of bridging linguistic knowledge and language use in SLA research and pedagogy, noting limitations of existing frameworks like procedural vs. declarative knowledge conversion and focus on form. It presented the xu-argument’s solution centered on borrowing language patterns for creating personal expression. The approach arose from practical classroom insights aiming to overcome inefficiency caused by decontextualized practice by tightly linking learning and use in authentic contexts.