There are several philosophical proofs for this fact. Ontological, Cosmological, Mystical and Theological proofs have been discussed in philosophical circles during last milleniums.

Charles Hartshorne in preface of his ontological book says: "I suspect that the future of the ontological problem lies largely in rather technical developments in formal logic. Only those who know the logic can promote or adequately judge. The stage of "talkitalk" about this matter is probably nearing its close." (1965)

Gödel worked on it and now mathematical proof based on the set theory and third order modal logic is available. Professor Melvin Fitting of mathematics department of The City University of New York formalized it in his book, Types Tableaus and Godel's God.

It is not easy to understand the proof for unskilled mind. In fact if one attempts to understand it finds it impossible if prerequisite mathematics and logical knowledge is not gained first.

But one who desires a rare jewel is prepared to travel to distant mountains.

Prerequisites

To understand the proof it is required to gain knowledge of the following subjects first. One can obtain the knowledge by reading books or choosing the easier path of going to the nearest University, Math or Philosophy departments and taking necessary logic courses. List of some necessary books that cover the prerequisites can be found in the reference section.

• Prepositional logic
• Predicate logic
• Proof trees
• Modal logic
• Possible worlds semantics
• Mathematical set theory

Familiarity with the following is also required but they are described in the first chapters of the book.

• Third order modal logic
• Classical logic basic tableaus
• Classical logic higher order tableaus
• Modal tableaus
• Schutte logic types