How do you write a thesis statement for an essay on "Seize the Day" by Saul Bellow?

Before writing your thesis statement, you need to
determine what will be the purpose of your essay.  Ask yourself, "What will my essay set
out to prove?"  If your teacher has given specific instructions or a prompt, your thesis
statement will essentially answer the question in the prompt.  If not, then you need to
determine an area on which you wish to concentrate.  Most often, the easiest thing to do
is to write about a theme of the story, and show what message the
author wishes to send, and how he accomplishes his
message.

In "Seize the Day," there are a few themes on
which you could write.  The most prominent is probably the idea of isolation.  Consider
that the story takes place in an urban setting just after WW2, when America's economy is
on a major upswing.  Certainly the main character experiences isolation and loneliness
living in this modern world in which he struggles to find his place.  On a bigger scale,
consider the message about all humans and how progress (economic or otherwise) often
comes at the cost of such isolation.  In times of struggle (like the Great Depression)
humans depend on one another.  When things are financially and otherwise more
comfortable, humans tend to race towards success
alone.

Other themes which stem from the above idea include
the pursuit of the "American Dream," the comparison of success and failure, and the
overall notion of how an individual finds his place in a society, especially one which
does not immediately appear to need
him.

As you explore the themes of the short story and begin
brainstorming ideas, eventually you should come up with a theme
statement which essentially answers the question: what is the author
trying to say about [selected theme subject] and how does he accomplish this?  Answering
this "what" of this question will give your essay one overall focus.  Then, you
establish your mode of organization and development by answering the
"how."