Dr. Krashen explains that this idea, The Monitor Hypothesis, shows how language learning (grammar) affects language acquisition. This is, according to Krashen, the useful outcome of learning grammar. It acts as a “monitor” of spoken language. Krashen postulates that this monitor brings refinement and correctness to speech. It acts to correct errors in speaking the second language.
He also suggests there are three kinds of people who use The Monitor Hypothesis to one degree or another. There are those who consistently use the monitor to correct their speech. There are those who never learned grammar or choose not to use grammar to monitor their speech. Then, there are those who use their deliberately learned grammar in an appropriate manner in the monitoring of their speech.
An extrovert, for example, tends not to use his deliberate learning of the grammar of the second language in actual communication events. Introverts, on the other hand, tend to be perfectionists in how they use what they know about the language (grammar) in the monitoring of their communication in the second language.
Academics tend to debate the issue of whether grammar...