***** NOT A TEACHER *****
Hello, Teacher Yasmein:
1. Your students are very lucky to have such a well-informed teacher (in my opinion).
2. According to one of the greatest grammarians ever to live (in my opinion), the possessive (or actually so-called
"genitive") progressed through hundreds and hundreds of years of development and change.
3. IF (a big "if") I understand him correctly, here is how the English people have expressed your sentence:
Jack
es shirt is gray.
Jack
s shirt is gray.
Jack
his shirt is gray.
(About the year 1680) Jack
's shirt is gray.
*
's became "widely used" because "doubtless" (this esteemed scholar tells us), many people felt that it was a
contraction of
his. (It was
not -- as I understand it.)
* Here are some examples given by the scholar:
Mary
her books.
The boys
their books
.
(The scholar says that
's cannot be a contraction for "her" or "their," of course. He says that it spread "by analogy.")
*****
Today in 2012, most teachers, I think, do not want to confuse their students with the history of the possessive.
So they tell their students to use
's correctly to indicate possession.
P.S. The great scholar reminds us that although today we write "This is Mr. Jones's house," we still pronounce it
as if
it were written "Jones
es."
That fantastic scholar was Professor Dr. George Oliver Curme. His 1931 two-volume masterpiece is called
A Grammar of the
English Language. (I have a 1983 reprint. I consulted page 71.)
HAVE A NICE DAY,
James