The past month I have run across an extremely powerful argument for the Christian God's existence and I want to share it with you all in an easy and accessible manner. 

It is called the Transcendental Argument for the Existence of God, or TAG for short.  It is also filed under Presuppositional Apologetics, but these big words don't really matter.  What matters is the meat of the argument:

Logic, science, and morality make no sense except in the light of the Christian worldview.  Stated differently, only Christianity offers a rational, non-arbitrary basis for logic, science, and morality.  What this means is that before the skeptic can even present his logical arguments against Christianity, he must first justify his use of logic, because the Christian using TAG is saying that by the skeptic using logic, he is assuming the truth of Christianity, which makes utter nonsense of all his arguments against this truth!  

That is a taste of the power of the argument.  Here is a bit on how the argument works:

Logic:

Why should the materialist believe the laws of logic?  They are not material, therefore they do not exist, according to his worldview.  He might respond that they simply work, but that does not answer the question.  The existence of immaterial laws of any kind refute his worldview that matter in motion is all there is.  He could say that laws of logic exist as abstractions in the mind, but again, this is nonsensical in the worldview that asserts that there is no such thing as abstractions or minds. 

On the contrary, laws of logic like the Law of Noncontradiction (Canada cannot be both north of the United States and not north of the United States) flow from the very nature of the Christian God.  The Bible states that the all-powerful God cannot deny Himself (2 Tim 2:13) and cannot lie (Num 23:19, Heb 6:18).  Further, Jesus, His Son, is described as the Logic of God (John 1:1, "Word" = logos, mind, reason, logic).  Christianity provides a very firm foundation for trusting the Laws of Logic, for God is a logical God.

Science:

Why should the atheist trust the basic assumptions of science, such as the Law of Uniformity, which states that an experiment performed today will behave identically tomorrow (given the same starting conditions).  Why cosmos instead of chaos?  If the atheist says that things have always behaved this way and there is great statistical chance that it will behave this way tomorrow, he is begging the very question asked, which is illogical!  

On the contrary, the Bible states that God sovereignly upholds His creation in an orderly fashion.  There exist laws of science because God has placed them there when He created the universe.

Morality:

On what basis can an atheist declare something is right or wrong?  Is it morally wrong that a lion kills an antelope?  According to atheists, we are just animals, a blip in the universe that is here now but soon will not be.  Yes, atheists can be moral; good atheists do exist.  But they borrow from the Christian worldview when they do so, meaning their own worldview is inconsistent.  

On the contrary, the Christian worldview offers a robust foundation for morality.  God is good and sovereign.  Morality flows from His very nature.

Summary:

A good analogy for this argument is like a guy who denies the existence of air:  "I don't believe air exists!"  You can reply back, "Well, you had to use air to tell me that."   Just as speaking words across a room requires air, communication and arguments require logic.  Which brings me to the title of this blog:  if you can read this sentence, God exists.  

Resources and Background:

TAG is a newcomer to arguments for the existence of God.  It began with Cornelius Van Til in the 1970s and 1980s.  He presented the argument, but died before he could flesh it out.  This task was left to his followers.  Greg Bahnsen developed the argument further in the 1980s and 1990s before he too died.  John Frame also contributed.

TAG was used by Bahnsen in the historic 1985 debate with Gordon Stein (atheist), which you can listen to here and read along with this transcript (PDF, HTML).  (Warning, the YouTube playlist is out of order near the end.)  Eleven years later, Gordon Stein admitted that he was unprepared for this new argument.  He claimed to have developed a rebuttal but as of 2009 I am unable to find it.  Stein died in 1996.  

Michael Martin (atheist) took the task of dismantling TAG seriously.  In 1996 he presented TANG, which is supposed to show TAG to be false.  What shocked me was that I was able to show two of his three main points to be false in the first reading!  Michael Martin is supposed to be a world-class atheist!  How am I able to take him on myself?!  John Frame and Michael Butler responded and confirmed what I had already caught, while dismantling the third point I wasn't able to.  

Internet Infidels page on TAG.  Note that this is 2009 and their latest document is from 2001.  Also note after reading them that atheists have yet to dismantle TAG.  My sense is that they even knew this when writing those documents; they don't sound confident.

My takeaway point from this is that TAG is extremely powerful and it still has a choke-hold on atheists.  I suggest Christians learn the basic points of this argument.

A good link:  http://butler-harris.org/tag/

Martin-Frame debate on Internet Infidels

Brief comment about other worldviews:

In this blog I pretty much focused on atheists.  I did this out of simplicity.  TAG is very distinctly a Christian argument, not a generic theistic argument.  Also, in order for this argument to work, it must be contrasted with another worldview/religion, as you saw above.  I did not show how TAG stands up against other worldviews/religions, but this is possible.  It comes down to whether any worldview or religion has built within itself any explanation for these three items:  logic, science, morality.  If a worldview or religion is internally or systemically contradictory, they can be eliminated outright, for how can a worldview or religion account for logic when it violates logic? 

I invite the curious to study this topic further.  I am not a professor and I feel I can only give an overview without introducing falsehoods on this topic.