Reading Comprehension Success in 20 Minutes a Day, 3rd Edition

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S u b j e c t v s . M a i n I d e a
There’s a difference between the 
subject
of a piece of
writing and its 
main idea
. To see the difference, look
again at the passage about the postal system. Don’t
skip over it! You read it in Lesson 1, but please read it
again, and read it carefully.
Today’s postal service is more efficient and reliable
than ever before. Mail that used to take months to
move by horse and foot now moves around the
country in days or hours by truck, train, and plane.
First-class mail usually moves from New York City
to Los Angeles in three days or less. If your letter or
package is urgent, the U.S. Postal Service offers Pri-
ority Mail and Express Mail services. Priority Mail is
guaranteed to go anywhere in the United States in
two days or less. Express Mail will get your package
there overnight.
You might be asked on a standardized test, “What
is the main idea of this reading?”
For this passage, you might be tempted to answer:
“the post office.”
But you’d be wrong.
This passage is 
about
the post office, yes—but
“the post office” is not the main idea of the passage.
“The post office” is merely the 
subject
of the passage
(
who
or 
what
the passage is about). The main idea
must say something 
about
this subject. The main idea
of a text is usually an 
assertion
about the subject. An
assertion is a statement that requires evidence (“proof”)
to be accepted as true.
The main idea of a passage is an assertion about
its subject, but it is something more: It is the idea that
also holds together or controls the passage. The other
sentences and ideas in the passage will all relate to that
main idea and serve as “evidence” that the assertion is
true. You might think of the main idea as a net that is
cast over the other sentences. The main idea must be
general enough to hold all of these ideas together.
Thus, the main idea of a passage is:
■
An assertion about the subject
■
The general idea that controls or holds together
the paragraph or passage
Look at the postal service paragraph once more.
You know what the subject is: “the post office.” Now, see
if you can determine the main idea. Read the passage
again and look for the idea that makes an assertion
about the postal service 
and
holds together or controls
the whole paragraph. Then answer the following
question: