A theory, hypothesis or concept from the study of how people acquire a first or second language, spanning the generative and nativist tradition (the innateness hypothesis, poverty of the stimulus, the language bioprogram theory), the classic second-language-acquisition hypotheses associated with Stephen Krashen and his successors (the input hypothesis, the natural order hypothesis, the interaction hypothesis, comprehensible output), the bootstrapping family of theories explaining how children break into grammar (syntactic, semantic and prosodic bootstrapping), and terms describing a learner's developing language system and its limits (interlanguage theory, fossilization, the critical period hypothesis, multi-competence). This group gathers material specific to language rather than general cognition or literacy instruction.