If you’ve ever been told that the key to language learning is exposure to material that’s just a bit harder than what you already know, you’ve met i+1.

It’s an idea that has a lot of currency in polyglot and language pedagogy circles; it’s a key concept in Stephen Krashen’s Comprehensible Input theory, and it has informed all manner of language courses. Quite simply, i+1 encapsulates the idea of microprogression:

i = your current level
+1 = a small, manageable stretch

It’s a simple idea. Read texts you mostly understand. Listen to language that’s familiar on the whole, but challenges you to understand new material from context. Do this often enough, and acquisition of rules and vocabulary will happen naturally, without heavy grammar instruction or constant correction.

It’s such an elegant, easily applied idea, and it’s shaped language teaching for decades. But a new paper has started asking whether input on its own is really enough.

A newer view: the brain doesn’t just absorb language

A recent article, Beyond comprehensible input: a neuro-ecological critique of Krashen’s hypothesis, doesn’t reject comprehensible input outright. Instead, it argues that it’s based on a too-passive view of learning. It’s something that’s dogged pragmatic language learners all along – does all that material really just work its way in via osmosis, and settle into neat patterns in our brains?

Drawing on neuroscience and embodied cognition, the paper’s authors suggest that the brain doesn’t, in fact, learn language by quietly soaking it up. It learns through interaction, action, and feedback.

In other words, understanding language matters. But doing things with it matters just as much, if not more.

From “input” to opportunities to act

A key concept in the paper is affordances: the opportunities an environment gives you to use language competencies (like listening, reading, writing).

• A podcast affords listening.
• A conversation affords responding, repairing, negotiating meaning.
• A task affords choice, intention, and consequence.

The argument is that input without action is weak. Learners may understand plenty, but without chances to respond or adapt, progress can stall.

This also explains a familiar polyglot experience: massive input can lead to excellent comprehension, yet hesitant or fragile speaking. If you’re a shy polyglot (not an oxymoron, I can assure you!), then you’ll know this practice gap – you can have great passive understanding, but lack practical confidence.

So what changes in practice?

Not as much as you might fear.

Comprehensible input still matters — but it works best when it’s embedded in interaction:

• reading and then reacting
• listening and then responding
• input that leads somewhere, rather than stopping at understanding

For teachers, this means designing tasks with feedback loops. For self-directed learners, it means pairing input with use: shadowing, retelling, chatting, or writing back.

A small shift with big implications

Krashen made a huge contribution to language pedagogy in helping move language learning away from drills and fear of mistakes. This newer perspective builds on that legacy, but nudges us from receiving language towards acting with language.

In other words, i+1 is still central to progression in language learning. It just turns out that +action is its vital partner — something we should all be mindful of, whether designing courses or working through our own language-learning projects.