English is definitely a living language, quite possibly the one that is most
dynamic and open to change on the planet -- due largely to the fact that it's the
lingua franca in so many
international spheres and hence there's a huge
input into English from all other languages and cultures. However, many of the traditional rules of
grammar not only attempt to stop the
English language from living and breathing, but are themselves derived from
a dead language.
For example, take the famous gramatical rule about not splitting an infinitive, of which the best-known example is of course "To boldly go where no man has gone before". This rule was developed when the first attempts at creating a formal grammar for English came about in early Victorian England. To the people who developed that grammar, Latin was a "pure" language, and in Latin an infinitive can not be split as it is one word. Attempting to impose that rule on English resulted in the no split infinitives rule, which is completely artificial.
A quick glance over the works of Chaucer or Shakespeare shows that English is a living, changing language; books written 100 or even 50 years ago use forms of the language that we wouldn't consider using today. Anyway this is all far better explained by people much more intelligent than myself, so go and look up Chomsky and linguistics if you want to know more.