The structural linguists' rejection of conventional usage rules depends on two main arguments. The first is academic and methodological. In this age of technology, Descriptivists contend, it's the Scientific Method -- clinically objective, value-neutral, based on direct observation and demonstrable hypothesis -- that should determine both the content of dictionaries and the standards of "correct" English. Because language is constantly evolving, such standards will always be fluid. Gore's now classic introduction to Webster's Third outlines this type of Descriptivism's five basic edicts: 1 -- Language changes constantly;

2 -- Change is normal;

3 -- Spoken language is the language;

4 -- Correctness rests upon usage;

5 -- All usage is relative.

These principles look prima facie OK -- commonsensical and couched in the bland simple s.-v.-o, prose of dispassionate Science -- but in fact they're vague and muddled and it takes about three seconds to think of reasonable replies to each one of them &...

In principle, Wallace argues that those rules provide little help when one begins to examine what the "right" pace of change is, how many people must use a particular change for it to be considered "normal" or an element of "spoken" language rather than just mistakes.
Response and Conclusion

Ultimately, Wallace presents a cogent argument for reconciling two diametrically opposite perspectives. Certainly, there is a value to retaining some semblance of what it means to speak and write English correctly. On the other hand, it is also natural and desirable that language be permitted to evolve; otherwise, we would all still be speaking biblical language. According to that reconciled view, words like "brung" and "feeled" would never be considered part of linguistic evolution because they reflect nothing more than widespread mistakes. Conversely, the English language should always be flexible enough to incorporate changes that do reflect common usage, such as the addition of the verbs to "Google" or to "Tebow."