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Explore the idea. This entry explains one question; it is not a systematic review.
The idea
In Krashen's account, i represents current competence and i+1 represents a next step beyond it. Context and knowledge of the world can help a learner understand a message that contains unfamiliar language. The formula does not give a test for assigning a number to either part.
A worked example
A learner hears ‘El gato duerme’ while seeing a sleeping cat. If the learner already knows gato, the picture may help them infer that duerme means ‘sleeps’. This illustrates a possible use of context; it does not prove that the learner has acquired the verb.
Choose material without a formula
After a short passage, say what happened in your own words. If you cannot identify the people or the main event, add a picture, transcript or explanation, or choose easier material. If you can follow the story but still notice something new, continue. These are practical checks, not a validated measurement of i+1.
A limit
Do not assume that one unfamiliar word is exactly one developmental step. The formula is a theoretical proposal, and its practical boundaries are difficult to measure. Read the original alongside the objections in our evidence guide.
Sources
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Cite this page
Jibber Jabber. "What does i+1 mean?." What Is Comprehensible Input?, updated 2026-11-09. https://whatiscomprehensibleinput.com/i-plus-one/
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This guide is one of a collection published by Jibber Jabber. The sites share one publisher and are not independent endorsements. See the related websites.