Learning and teaching Second language is not easy and is not simple case. It takes many variables of the learners when they must think, feel and act in the second language; when they must leave their first language and come into the new language, and demand teacher to know and understand every variable that is taken from the learners. That is why only few people are able to success in learning the second language well.
Here, I will simply talk about the variables; including some theories had been created by many linguists since a century ago.
What is language?
It is impossible to teach something when we do not know what we will teach. So, when we will teach a language,