The history of language study illustrates widely divergent
attitudes concerning the relationship between writing and speech.
Written language was the medium of literature, and, thus, a
source of standards of linguistic excellence. It was felt to provide
language with permanence and authority. The rules of grammar
were, accordingly, illustrated exclusively from written texts.
The everyday spoken language, by contrast, was ignored
or condemned as an object unworthy of study, demonstrating
only lack of care and organization. It was said to have no rules,
and speakers were left under the illusion that, in order to “speak
properly”, it was necessary to follow the “correct” norms, as laid
down in the recognized grammar books and manuals of written
style.
There was sporadic criticism of this viewpoint throughout
the 19th century, but it was not until the 20th century that an
alternative approach became widespread. This approach pointed
out that speech is many thousands of years older than writing;
that it develops naturally in children (whereas writing has to be
artificially taught); and that writing systems are derivative —
mostly based on sounds of speech.
D. Crystal. How Language Works. London: Penguin Books, 2006 (adapted).