Second language acquisition theory, developed through Krashen, Vygotsky, and their successors, distinguishes between acquisition (unconscious naturalistic development through meaningful input) and learning (conscious rule-focused study) — and establishes that acquisition is primary and more powerful. The comprehensible input hypothesis holds that language develops through exposure to material just beyond current competence — Vygotsky's zone of proximal development applied to language. These findings have profound implications not only for language pedagogy but for the design of any learning environment.
Each step builds on the last.