Monitor Hypothesis
The monitor hypothesis is one of Stephen Krashen's five hypotheses of second-language acquisition, proposing that consciously learned grammar rules function as an "editor" or monitor that can check and correct output produced by the acquired system — but only when the learner has sufficient time, focuses on form, and knows the rule.
Krashen drew a sharp distinction between acquired language — language absorbed implicitly through comprehensible input, which drives fluent spontaneous production — and learned language, which consists of explicit grammar rules studied consciously. The monitor hypothesis states that learned language cannot directly produce fluent speech; it can only "monitor" output initiated by the acquired system.
Three conditions must all be met for the monitor to operate: the learner must have adequate time (impossible in fast natural conversation), must be focused on correctness (rather than meaning), and must know the relevant rule. In practice, all three conditions are rarely met simultaneously in real conversation, which is why Krashen concluded that conscious grammar knowledge has a very limited role in fluent communication.
The monitor is most useful in writing and careful prepared speech, where time is available. It is least useful in spontaneous conversation, where the time constraint alone prevents effective monitoring. Krashen advocated keeping the monitor at an optimal level: not so over-used that it inhibits fluency, not so ignored that errors pile up in formal written production.
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FAQ
What is the monitor in Krashen's theory?
It is the internal "editor" formed by consciously learned grammar rules. It checks output produced by the acquired system before the learner speaks or writes.
When can the monitor be used?
Only when three conditions are met simultaneously: the learner has enough time, is focused on form, and knows the relevant rule. This rarely happens in fast natural conversation.
Can grammar study replace comprehensible input?
No, according to Krashen. Conscious grammar learning feeds the monitor (editing), not the acquired system (fluent production). Fluency requires large amounts of comprehensible input, not more grammar rules.