Monitor Hypothesis (Stephen Krashen)
Explanation of Main Features
As second language learners are in the process of acquiring and learning a language, they are also learning the rules of how to use it. The Monitor is a tool learned by students to implement during the process of sending a message orally or as written language and “detects errors and repairs them before or after attempted communication” (Diaz, Rico, 2006, p 57-58). As the language learner is producing language, orally or in writing, they Monitor their output to insure that it is grammatically correct, making it easier for the listener or reader to comprehend the message. Krashen believes that language learners are more capable of implementing their monitors if they have time to think about their message, are able to focus on language form, but most importantly, know and understand the grammar rules that they are trying to use to correct themselves (Krashen, 16). A language learner is more likely to use the monitor when all three of the previously conditions are met, but it does not mean that they will always be used. Also, it is much easier for a language learner to learn and use the monitor when the grammar rules that they are learning are simple in nature.
In Krashen’s works, he states that there are three types of language learners who use the monitor, monitor over-users who speak hesitantly, without fluency, and self correct often; monitor under users who correct without using their knowledge of grammar rules and only when an error doesn’t “feel” right; and the optimal monitor user who makes corrections appropriately and the corrections do not interfere with communication. In writing and in a planned speech, optimal users will make corrections as necessary.
Classroom Implications
Teachers of language learners need to make sure that the classroom environment for their learners is comfortable and safe for the learners to use their newly acquired language. When this is the case, students will be able to produce more language and slowly develop their monitor with guidance from their teacher and classmates. Over correction of the language learners as well as inauthentic language, and a large quantity of grammar activities will make it difficult to develop a monitor.

Teachers should:
--encourage students to be "optimal monitor users" (to use the monitor when appropriate and when it doesn't interfere with communication).
--teach grammar through meaningful activities in the context of authentic communication
--model proper grammar use.
--not over-correct learners
--create a low anxiety atmosphere and allow beginning learners time to go through their "silent period."

Critique
The successful results of the Canadian students in the French immersion program caused Swain to question Krashen’s “argument that comprehensible input was ‘the only true cause of second-language acquisition’ (Krashen 1984: 61)” (2008) Swain proposed that instead of language being a “medium of data collection,” (2008) it is its own source of language learning. When students recognize that their output is incorrect, seek feedback on their output, and imitate others they are forming a new understanding of their language skills and seeking an improved way to communicate their meaning. The process of “creating comprehensible output facilitates their language acquisition.” (Wright, 2010, p. 41)
References
Diaz-Rico, L. T., Weed, K. Z. (2006) The crosscultural language and academic development handbook. Boston, Massachusetts: Pearson Education INC.

Krashen, S. D. (n.d) Principles and practice in second language acquisition.
Swain, M. (2008). The output hypothesis: its history and its future. A keynote speech in The 5th Annual International Conference on ELT in Beijing. Retrieved May 11, 2011 from http://www.celea.org.cn/2008/keynote/ppt/merrill%20Swain.pdf.
Wright, W. E. (2010). Foundations for teaching English language learners: Reseach, theory, policy, and practice. Philadelphia: Caslon Publishing.