In 1982, linguist Stephen Krashen published a work that turned the language teaching world upside down. He proposed that the way human beings acquire a second language is fundamentally different from what traditional schools teach — and that most conventional methods were wrong.
Decades later, science continues to prove him right. Understanding his 5 hypotheses can completely change the way you learn English.
Hypothesis 1: Acquisition vs. Learning
This is the foundation of everything. Krashen makes a clear distinction between two different processes:
- Acquisition: an unconscious, natural process, similar to what a child does when learning their mother tongue. You absorb the language without thinking about it.
- Learning: a conscious process involving studying rules, memorization, and formal grammar.
The crucial point is that acquisition and learning are separate systems in the brain. And only acquisition produces natural, fluent speech. Conscious grammar learning may help with formal writing, but it’s not what makes you speak without freezing.
Practical implication: if you spent years studying English grammar but still can’t speak, it’s because you studied — but didn’t acquire.
Hypothesis 2: The Natural Order
Krashen observed that grammatical structures of a language are acquired in a predictable order, regardless of how and when they are taught. This means you can’t force the acquisition of a grammatical structure before the brain is ready for it. Teaching too early doesn’t work — the brain registers it, but doesn’t incorporate it.
Hypothesis 3: The Monitor
The Monitor is the conscious grammar system you activate when editing what you’re about to say or write. It only works when you have time to think, know the rule, and are focused on form — not meaning.
In real conversations, the Monitor is almost useless. There’s no time to activate it. Fluent speakers aren’t conjugating verbs in their heads — they’re simply speaking. The problem is that many students use the Monitor as a crutch all the time, which freezes speech.
Hypothesis 4: Comprehensible Input (i+1)
This is Krashen’s most famous hypothesis — and the most powerful.
You acquire a language when you are exposed to input (content: speech, text, audio) that is slightly above your current level of understanding. Krashen calls this i+1: your current level (i) plus one step beyond (+1).
- Input that’s too easy (i-1): no learning. You understand everything, but don’t advance.
- Input that’s too hard (i+5): you understand nothing. Also no learning.
- Comprehensible input (i+1): you understand most of it, and context helps you infer the rest. This is where acquisition happens.
In practice: a show you understand 80% of is more useful for your learning than a course you understand 40% of.
Hypothesis 5: The Affective Filter
The affective filter is the emotional barrier that blocks acquisition. When you’re anxious, afraid of making mistakes, or in a high-pressure environment, the filter rises — and even if comprehensible input is right there, the brain doesn’t absorb it effectively.
Safe environments, encouraging teachers, and low-pressure situations lower the filter. That’s why children learn languages faster: they’re not ashamed to make mistakes.
What This Changes in Practice
- Replace some grammar study time with consuming content in English.
- Choose content you understand ~80% of, not 40%.
- Create practice environments where you feel safe to make mistakes.
- Stop using the Monitor as a filter in conversations — trust what you’ve already acquired.
The book “Unlocking Language,” by the Nicola Valone Method, is entirely built on Krashen’s principles — translated into the reality of the Brazilian learner.