Taken from the book "Principles and practice in second language acquisition" wrote by Stephen Krashen.
Principles and Practice in Second Language Acquisition
I. Introduction: The Relationship of Theory to Practice
There are three different ways of arriving at answers in methodology and materials:
1. Theory of second language acquisition. THEORY
Theoretical linguistics, it consists of a set of hypotheses that are consistent with the experimental data.
2. Applied linguistics research. PRACTICE
2. Applied linguistics research. PRACTICE
It’s not aimed at supporting or attacking any coherent theory but rather at solving practical, real problems that confront society.
3. Ideas and intuitions from experience. INSIGHT
It doesn’t rely on experimentation at all but on the insights and observations of experienced languages teachers and students of foreign languages, it doesn’t need any empirical support, the word of the teachers is sufficient evidence.
In an ideal world, information should be flowing between all the three areas. Today, there is very little interaction between and among the three areas.
Some failures have been: Direct application of the principles of behaviorist psychology in the classroom, audio-lingual method, or when theoreticians insisted that “dialogue and pattern drill” was the way to teach language.
What current theory implies, quite simply, is that language acquisition, first or second occurs only when comprehension of real messages occurs, and when the acquirer is not “on the defensive”. It doesn’t occur overnight, it develops very slowly and speaking skills emerge significantly later than listening skills, even when conditions are perfect.