Mini rant about "learning through comprehensible input" and the many situations it's used to mean somewhat different things:
In traditional language learning, using classrooms and textbooks, grammar guides and flashcards: comprehensible input are the dialogues/paragraphs in your textbook that you get a vocabulary translation list for and grammar explanations for so you can comprehend it. It can also be tutoring sessions, where you talk with the tutor and they use translations and gestures and visuals to make sure you can understand them. Once you reach a decent level of understanding the language, comprehensible input becomes any regular material for native speakers you can understand the main idea of (or more). So if someone who took classes for years is telling you to immerse in materials for native speakers, they probably assume you have some prior knowledge about the language and can understand the materials for native speakers to a degree. If a teacher is recommending you immerse in the language, they probably mean to immerse with content that uses words/situations you've studied in class at some point. These people do NOT mean for a brand new beginner, who knows nothing, to just go sit and watch movies for adults in the target language and magically learn over time.
In Refold/Mass Immersion Approach community, online communities where the study method involves a lot of flashcards/anki/SRS/apps with vocabulary/making word or sentence lists with translations: when they say comprehensible input, they mean material you can understand the main idea of, with the help of looking up word translations and grammar! They usually expect you will at least look up some key words once in a while, or immerse with stuff that uses words you've recently studied (in anki). When they say "immerse a lot and often" sometimes they do mean to immerse with input you do NOT understand, but when they're saying to get mostly comprehensible input, they mean either stuff made for learners to be understandable OR you using tools like word translation to be able to understand the material. There are people who did try to immerse with input they did not understand (maybe because they didn't understand the advice to immerse in materials for native speakers), without looking up words or using any tools to help them understand, and thousands of hours later they still were beginners. The people who successfully have used anki and immersion to learn a language, usually mean using immersion material that you can comprehend the main idea of (with tools/aids if necessary like word translations or word definitions in the target language). Notice that for these learners, comprehensible input MAY NOT BE comprehensible if you're relying on ONLY what you already know, and may require TOOLS to be comprehensible. They're expecting you to USE TOOLS to make the input comprehensible! (Flashcards, definition lookups in target language, word translation lookups, grammar explanation lookups).
Comprehensible Input Method/Automatic Language Growth/Nature Method Learners: By comprehensible input, they mean only materials you can understand the main idea of (without needing tools/aids). This will initially be materials MADE FOR LEARNERS, like the Nature Method textbooks with illustrations to explain the meaning, and Comprehensible Input lessons on youtube where the teacher shows you pictures and uses gestures to communicate the main idea. Then the materials may be graded readers made with a vocabulary a learner is expected to know, and possibly a vocabulary list in the back. And podcasts for learners, that use a limited number of words they expect the learner to know and define new words. Eventually, this can mean cartoons for toddlers where the visuals about what is being said, in addition to the words you already know, makes the main idea understandable. Then eventually cartoons for older kids, and shows, novels for kids, and novels for adults, etc as you learn more words and understand more (without needing tools/aid). So the key here, is this kind of learner usually means MATERIALS you can understand without any tools! This is a huge difference from the Refold learners, who often mean comprehensible input as ANY input if you're using enough tools TO comprehend it.
ALL of these learners usually mean, by comprehensible input, materials you can understand the main idea of - with or without tools. If you cannot understand the main idea - use tools! If you can understand the main idea, cool, you comprehend it enough to learn from it! None of these learners are trying to suggest beginners trying to learn a target language just listen to adult radio in the TL for 2000 hours and somehow 'learn.' All of these learners think a beginner NEEDS either a lot of visuals to allow for understanding (comprehensible input lessons, nature method), so the learning aid is built INTO the materials initially. Or these learners think beginners NEED to use tools to make materials understandable (translations, dictionary entries, anki to memorize words, textbooks), to be able to learn from materials. In either case, the advice to use comprehensible input assumes you are comprehending the main idea being conveyed in the material, and if needed you're using additional tools/aids/resources to figure out the main idea being conveyed.
There's a guy on youtube who keeps making these videos about using input to learn japanese, and I overall agree with him. But he only mentions a few times he uses anki to study (so uses tools to understand more), and he learned a decent number of words before using audio-only as input to study with (so he could comprehend the main idea to a degree), and the impression I get from comments is that some people sincerely think he's saying to listen to regular japanese materials for adults for thousands of hours and that itself will be enough to learn. I don't think he necessarily makes it clear how much initially VISUAL input is better if someone is going to just watch materials in japanese, how much his explicit study with anki may be increasing what he can comprehend, and how much using materials-made-for-learners works better in the beginning (he does recommend learner podcasts like Nihongo Con Teppei and Learn Japanese with Shun). I think the guy's heart is in the right place, and he's got good advice. I just get frustrated with how MANY people are misunderstanding his advice. Especially beginners, who may think when he says immerse in content you only understand 10% of... he is assuming the beginner is looking up key words, and making new anki cards of words they're hearing to study more.
As a learner... please don't bash your head into content you don't understand the main idea of for hundreds of hours. I am begging you, do something like look for materials MADE FOR LEARNERS to be understandable (comprehensible input lessons, graded readers, textbooks, sentences with translations, dialogues, or even cartoons with clear visuals about what is going on), or USE SOME TOOLS to make things understandable to you! Please...
