Comprehensible input for Mandarin, practically
Stephen Krashen's input hypothesis says you acquire a language by understanding messages just above your level — input at 'i+1': everything you know, plus one step. Four decades of classroom results and a thriving corner of the internet back the intuition. The catch is that Chinese is unusually good at making input incomprehensible: an alphabetic language leaks meaning to a beginner through cognates and spelling; Chinese text is a wall until characters are learned, and Chinese speech runs on tones your ear hasn't built yet.
What i+1 actually requires
The definition is strict: you should understand nearly everything, with the new material inferable from context. Reading at 70% comprehension is not comprehensible input — it is decoding practice. The practical bar sits near 95–98% known words, which is far tighter than most 'just watch native shows' advice admits. Getting Chinese input to that bar at every stage of your level is the entire game.
The ladder that exists
Graded readers rewrite stories inside fixed word lists; learner podcasts speak slowly inside a controlled vocabulary; comprehensible-input YouTube channels act meaning out visually. All of it works, and the honest ranking is by how close each source gets to YOUR 98% — a 'beginner' story using two hundred words you don't know yet is native content in disguise.
The limit of every pre-made source is the same: it is leveled for an average learner, not for you. Your known-word inventory is specific — it includes the food words you binged and lacks the transport words you skipped — and the mismatch is exactly where comprehension breaks.
Input at exactly your level, generated
This is the problem OptimalChinese was built around. The app tracks every word and pattern you know and generates review sentences from precisely that inventory, plus the single item being taught — i+1 made literal instead of approximate. Every review is input you can read; every new word arrives with nowhere to hide; and the sentence changes on every encounter, so you rehearse the language rather than the card.
Input is necessary, not sufficient
Krashen's strongest claims — that study contributes nothing — have not aged as well as the core insight. For Chinese in particular, some deliberate work on tones, characters and high-frequency grammar demonstrably speeds up how fast input becomes comprehensible. The productive frame: study exists to unlock input, and input does the acquiring. Spend your study minutes where they open the most input — frequency-ordered vocabulary, the grammar patterns you meet everywhere — and your input hours anywhere you enjoy enough to stay.
Everything above is built into the app: i+1 sentences, three faces per word, FSRS timing. Try it on your own vocabulary.
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