This paper attempts to review second language acquisition theory and some of the methods practiced in language classes. The review substantiates that comprehensible input as the crucial determining factor for language acquisition and consciously learned linguistic knowledge can be used only to edit the output of the acquired language sometimes before or after the production. It is also confirmed that the process of acquiring a second language is similar to the process acquiring L1 and, therefore, the teaching method that provides more input is more effective than the method that insists on conscious learning.