Does Santa Exist is easily the funniest philosophy book of the year. Not that it isn't serious. The book is a straight-ahead discussion of the nature of reality, posing as its central question not whether or not Santa Claus actually lives and walks among us but instead in exactly what ways does he -- and by extension, everything else -- live?

Sounds like a real barrel of laughs, right? Well, Eric Kaplan, a doctoral candidate in philosophy at Berkeley, is also a top-gun comedy writer who has written for David Letterman, The Simpsons, Malcolm in the Middle and other shows. He is currently a writer and co-executive producer for The Big Bang Theory. Clearly, here is a man capable of coming at the question from more than one perspective.

The issue event that led to his investigation of Santa's reality was a conversation with a friend, Tammi, whose son and Kaplan's son were scheduled to go to the zoo together. Tammi called to cancel the trip because she'd discovered that Kaplan's boy did not believe in Santa Claus and her son still did; she didn't want her son to be told that Santa didn't exist because she wanted to protect his innocence a little longer.

Searching for an explanation for Tammi's behavior, Kaplan generated two possible theories. First was the liar's theory, which states that somewhere along the line people made up the idea of Santa, probably to control the behavior of their children. When they grew up and no longer believed, those children lied to their own children, keeping the lie about Santa alive. As a result, we all belong to one of two classes of people: the liars and the lied to.

The second explanation, the crazy theory, declares that our minds are disassociated, capable of holding two contradictory ideas at once. When Tammi is around her child, she believes in Santa; when she is not, she does not. The crazy theory, then, says belief is conditional, depends on what the circumstances are at the time.

From there, Kaplan goes on to discuss how things can be real and not real simultaneously, looking a the question from three perspectives: logic, mysticism and comedy. Each, he says, has strengths and weaknesses; none can totally solve the problem by itself. At one point, he even goes into neuropsychology, discussing brain research to see how it contributes to the question. The right brain, Kaplan declares, is mysticism, while the left is logic.

Of course, considering what he does for a living, Kaplan believes comedy is the strongest approach, coming closest to explaining the paradox for several reasons: comedy is comfortable with -- and, in fact, deals in -- paradoxes, and comedy blends logic and mysticism.

Does Santa Exist is a serious book. Kaplan explores huge questions in depth and he knows his material. What makes it funny is his approach and his use of language. Even as he writes about abstract philosophical issues, he recognizes that there's a certain surface absurdity, a sense that humor is our only salvation in the face of questions that we can't really answer.

Kaplan makes a potentially difficult idea accessible and delightful. Anyone with an interest in the nature of reality or philosophical questions in general will love this book.