The Cat in the Hat was written in 1957. When Teddy wrote this book, he laced it with political jibes and subtle details portraying the major social issues of the time.
On a very basic level, let's take a look at the mother in the story. When we see the mother's room, she is sleeping in a twin-sized bed. There is no mention of a father at any point in this book.
The mother is apparently a single mom, and at the time, both illegitimate children and divorce (the two most likely causes of single parenthood), were controversial issues and looked upon with disdain.
The Fish from The Cat in the Hat Copyright © 2010 Random House LLC
On a deeper level, Dr. Seuss introduced religion and government. The children in the story represent us, the people. The fish is the metaphorical voice of morality and conscience, or Christ, depending on whether you choose to look at the book politically or religiously. In fact, some biographers believe he chose the fish because of its Christian symbolism. Seuss himself compared the fish to Cotton Mather, strict Puritan prosecutor during the Salem Witch Trials.
Throughout the story, the fish is the small voice nudging the children to do the right thing and stand up against the cat.
The Cat from The Cat in the Hat Copyright © 2010 Random House LLC
This brings us to the cat. The cat could represent Satan or society at large. He brings in many shiny exciting things, which he tells the children are fun. He tells them to look at this or that, all the while dazzling them with things that appear to make them happy and even mocking the fish's protests. Meanwhile, all of his "fun" is wreaking havoc around them.
Thing One and Thing Two from The Cat in the Hat Copyright © 2010 Random House LLC
The cat introduces Thing One and Thing Two, who represent sin and immorality. They seem new and exciting at the moment, but the whole time, the kids can see that something is not quite right about them.
Thing One and Thing Two escaping from their box. The Cat in the Hat Copyright © 2010 Random House LLC
Some people have gone so far as to claim the box from which Things One and Two come represents Pandora's box. Whether or not Dr. Seuss intended this representation is unclear, but the resemblance leaps off the page.
In the end, the children make their decision, put their foot down, and kick out the cat, his toys, and Thing One and Thing Two, thus removing the sin and immorality from their lives.
All illustrations are the work of Theodor Seuss Geisel. Copyright © 2010 Random House LLC