In Krashen's theory of second-language acquisition he claims that there is distinction between language acquisition and language learning, a distinction which other second-language acquisition researchers have called “perhaps the most important conceptualization” in the field and which has made possible the most productive models of SLA. According to Krashen, acquisition is a subconscious process, while learning is conscious. Although both play a role in developing second-language competence, acquisition is far more important, since the competence developed through it is responsible for generating language and thus accounts for language fluency. The second-language student can use learned rules to "monitor" or correct his language either before or after the moment of production. Monitoring serves a limited function, however, since it can operate only when there is sufficient time, when the focus is on form, and when the necessary rule has been learned. According to Krashen, learned competence and acquired competence develop in very different ways. In his view, language learning occurs through the formal study of rules, patterns, and conventions, a study which enables one to talk about and consciously apply the knowledge gained. Language acquisition, however, occurs quite differently, for it develops exclusively, Krashen believes, through "comprehensible input." That is, secondlanguage students acquire language competence by exposure to language that is both understandable and meaningful to them. It is in this context the present study is undertaken, to validate Krashen's theory, and the article has conducted an extensive review of literature from Google scholar, Scopus, ERIC and other sources.