This document discusses different types of language input that can contribute to second language acquisition (SLA). It examines pre-modified input, interactionally modified input, and modified output as three potential sources of comprehensible input according to some researchers. Pre-modified input involves modifying language before learners see or hear it. Interactionally modified input refers to modifications made during interaction with native or proficient non-native speakers. Modified output occurs when learners modify their language in response to input through interaction. The document also discusses other potential types of input like incomprehensible input and comprehensible output that may enhance SLA. It concludes that while language input is important for SLA, different types of input beyond just comprehensible input can support