Free download of : Principles and Practice in Second Language Acquisition – Stephen D Krashen
The first area we will discuss will be the central focus of this volume, second language acquisition theory. As developed today, second language acquisition theory can be viewed as a part of “theoretical linguistics”, i.e. it can be studied and developed without regard to practical application. As is the case with any scientific theory, it consists of a set of hypotheses, or generalizations, that are consistent with experimental data. These hypotheses can be arrived at using any of a variety of means (a brilliant insight, a dream, etc.). They must, however, be able to predict new data. In other words, hypotheses are not summaries or
categories for existing data and observations, but must pass the test of accounting for new data. If our current hypotheses are able to predict new events, they survive. If they fail, even once, they must be altered. If these alterations cause fundamental changes in the original generalizations, the hypotheses may have to be totally abandoned.
Note that according to this way of doing science, we can never really prove anything!
We can only look for “supporting evidence”. When we do not find supporting evidence, or when we find counter-evidence, our hypothesis is in trouble. Even when we do find supporting evidence, when the hypothesis makes the correct prediction, a critic can always say that we have not found “enough”. Thus, a scientist, professionally speaking, is never able to state that anything has been “proven”. All the scientist can do is have a current hypothesis that he or she is interested in testing ……..