So, what exactly is comprehensible input? The concept comes from one of my favorite linguists, Dr. Stephen Krashen. In his Theory of Second Language Acquisition, he states that students are able to acquire new language when instruction is delivered in language just beyond students’ current level of proficiency. Comprehensible input is simply an instructional shift when teachers provide input where students understand most, but not all, of the language.
BICS and CALP are both language acquisition skills, but of very different calibers. BICS is the Basic Interpersonal Communication System that second language learners use in any conversational setting, making it making a very contextualized form of the language. CALP is the Cognitive Academic Language Proficiency skills that second language learners use in setting such as the classroom. It is considered a very abstract and decontextualized form of the language.