What is Comprehensible Input (CI)? Comprehensible input means that listeners should be able to understand the essence of what is being said or presented to them despite them not understanding all the words and structures in it. Comprehensible input is a critical concept for second-language development for students with and without learning difficulties. Comprehensible Input, or CI , is the best way to acquire a language naturally. CI refers to the target language that students hear in class and even though they may not be understanding each and every word, they begin to recognize certain structures through repetition. You might have slightly understood what CI is by seeing these definitions. Let's experience CI from directly from the master.