Grammar Puss

If language is as instinctive  to 
humans as  dam-building is to
beavers, if every 3-year-old is a grammatical genius, if the design of syntax
is coded in our DNA and wired into our 
brains,  why,  you might 
wonder,  is  the 
English language in such a mess? 
Why does the average American sound like a gibbering fool every time he
opens his mouth or puts  pen to


The contradiction begins in the fact that the
words “rule” and “grammar” have very different meanings to
a scientist and to a layperson.   The  rules 
people learn  (or  more 
likely,  fail  to 
learn) in school are called [prescriptive] rules, prescribing how one
“ought”  to  talk.   
Scientists  studying  language propose  [descriptive]  rules,  describing 
how  people [do] talk — the way
to determine whether a construction is “grammatical” is to find
people  who  speak the language and ask them. 
Prescriptive and descriptive grammar are completely different things,
and there is a good  reason  that 
scientists  focus  on 
the descriptive rules. Steven Pinker, The New Republic