Dear Dr. Jamshid
To your statement nr.3 - "when children start speaking it is lexis, not grammar, which dominates..."
My question is: dominates what - the brain, the learning?
Children are born with a remarkable language expertise: they have the grammar already in their brain (not the conventional notion of Grammar as we use it in textbooks). All they need is words to define their world.
Noam Chomsky wrote a very controversial theory, namely that there is a so-called "universal grammar" (common to all human languages) that argues that "the human brain contains a limited set of rules for organizing language. In turn, there is an assumption that all languages have a common structural basis. In other words, with a limited set of grammar rules, humans are able to produce an infinite number of sentences, including sentences no one has previously said". That explains how children, when hearing grown-ups speak faulty English (grammatically), they don't immitate or reproduce these errors, but put the sentence the right way. In other words, grammar is the frame of language - you figure out on your own that smth is wrong with it, or else it will collapse.
Also, the presence of creole languages is cited in his work as further support for this theory. These languages were developed and formed when different societies came together and devised their own system of language. Originally these languages were pidgins and later became more mature languages that developed some sense of rules and native speakers.
Such languages all share certain features. Each language, syntactically, uses particles to form future and past tenses and multiple negation to deny or negate. Another similarity among these languages, that Chomsky highlights, is very important: that by changing inflection rather than changing words, a sentence or a question can be implemented. You said previously that meaning is mostly being made with the help of vocabulary, not grammar, but here you have an example that grammar, too, plays an important role in the establishing of meaning, not only words.
Now to some history of English grammar:
The original Old English (or Anglo-Saxon) language was fully inflected in the 9th c. A.D., but its grammar has changed. Why this loss of the noun endings? Because of the Norman Invasion of the 11th century, when English as a language came under the influence of French, not only in terms of words and manners of speech, but also in terms of French grammar functions. French does not have case forms for the noun.
So, English grammar has changed greatly across the centuries, not only its lexis. Now, with all the Englishes around the world, and the need for speed of communication, will E grammar survive as we know it today? Will they devise their own system of an English language? Or will their impact on E grammar NOT be so strong as French was centuries ago?