In this chapter, I aim to address the nature and conceptual foundation of comprehensible input (CI), namely existing views about and definitions of CI. Firstly, I focus on what the concepts input, comprehensibility, output and CI entail. Secondly, I examine what input's linguistic (e.g. phonological, morphological), cultural (e.g. practices, perspectives), semiotic (e.g. semiosis, indexical) and stylistic (e.g. register, formality) elements are. Then, I explicate how CI pertains to processing and output production. I conclude the chapter with a brief section that offers a broad perspective of CI in light of the cumulative wisdom accrued as a result of many theoretical and practical innovations in related fields.

Comprehensible Input

Human beings use language not only to construct concepts and metaphors but also to communicate reason, emotion and ideas (Lakoff & Johnson, 1980). If to communicate is to understand and be understood in different contexts of situations, successful communication depends largely on possessing and effectively using commonly shared units of language. Even the most common everyday communicative acts have an underlying assumption of shared understanding of linguistic forms and meanings. For instance, at the most basic communicative level, a child and a parent have to agree on the meaning of the utterance 'I'm hungry' to result in the parent giving the child food. In the academic world, for instance, technical terms (register) constitute a commonly shared basis for scientific communication among professionals in closely related fields. Without them, mutual intelligibility is impossible and the future of scientific advancement is in jeopardy. Indeed, the practical value of an innovative idea or a technical term resides in the adoption and dissemination of its shared understanding in the scientific community. In this sense, technical terms help researchers to label scientific phenomena and establish commonly shared roadmaps for communication. Conventionally, before a technical concept is added to a professional registry, it must undergo an adoption process. This could occur in two different ways. In the first way, the term is operationally defined by the theorist and the field adopts this definition.