The Great Debate: Does God Exist?

It became known as “The Great Debate.” In 1985 the University of California at Irvine hosted a public debate between philosopher Greg Bahnsen and atheist Gordon Stein on the topic “Does God Exist?”


Stein came prepared to cut down traditional apologetic arguments for the existence of God, but the philosopher’s approach was unexpected. Bahnsen went on the offensive and presented the Transcendental Argument for the Existence of God: the God of the Bible must exist because no other worldview makes rational sense of the universe and logic, science, and morals ultimately presuppose a theistic worldview. He explained:

The transcendental proof for God’s existence is that without Him it is impossible to prove anything. The atheist worldview is irrational and cannot consistently provide the preconditions of intelligible experience, science, logic, or morality. The atheist worldview cannot allow for laws of logic, the uniformity of nature, the ability for the mind to understand the world, and moral absolutes. In that sense the atheist worldview cannot account for our debate tonight.

Remembering the debate, philosopher and theologian John Frame writes,

I was there, having driven up with several students from Westminster in Escondido. It was in a large lecture hall at U. C. Irvine, and the place was packed. The atmosphere was electric. I don’t know how many were Christians, but it was evident as the debate progressed that the audience became convinced that Bahnsen won the debate.


Bahnsen’s approach focuses on the “presuppositional conflict of world views” between atheism and Christianity. In the debate he shows that his opponent has a precommitment to the rule that logic or reason is the only valid way to prove any statement. The atheist can’t prove this rule by using logic (that would be circular reasoning), or by any other method (that would be disproving the rule by using something other than logic). This is a presupposition, a fundamental belief held ahead of time that cannot be proved, but that grounds all your other beliefs. Bahnsen argues that the atheist is actually borrowing logic from the Christian worldview in order to make his claims.

In his book Van Til’s Apologetics, Bahnsen gives a formal definition of a presupposition:

A ‘presupposition’ is not just any assumption in an argument, but a personal commitment that is held at the most basic level of one’s network of beliefs. Presuppositions form a wide-ranging, foundational perspective (or starting point) in terms of which everything else is interpreted and evaluated. As such, presuppositions have the greatest authority in one’s thinking, being treated as one’s least negotiable beliefs and being granted the highest immunity to revision.

Presuppositions can be exposed and used to show that non-Christian worldviews are not rationally coherent:

The presuppositional apologist makes an internal critique of the non-Christian’s espoused presuppositions, showing that they destroy the very possibility of knowledge or ‘proof.’ He maintains that only Christianity is a reasonable position to hold and that unless its truth is presupposed there is no foundation for an argument that can prove anything whatsoever. Thus it is irrational to hold to anything but the truth of Scripture. The truth of Christianity is proved from the impossibility of the contrary (Presuppositional Apologetics: Stated and Defended).


He also explains further about arguing from the impossibility of the contrary:

The unbeliever attempts to enlist logic, science, and morality in his debate against the truth of Christianity. Van Til’s apologetic answers these attempts by arguing that only the truth of Christianity can rescue the meaningfulness and cogency of logic, science, and morality. The presuppositional challenge to the unbeliever is guided by the premise that only the Christian worldview provides the philosophical preconditions necessary for man’s reasoning and knowledge in any field whatever.

This is what is meant by a ‘transcendental’ defense of Christianity. Upon analysis, all truth drives one to Christ. From beginning to end, man’s reasoning about anything whatsoever (even reasoning about reasoning itself) is unintelligible or incoherent unless the truth of the Christian Scriptures is presupposed. Any position contrary to the Christian one, therefore, must be seen as philosophically impossible. It cannot justify its beliefs or offer a worldview whose various elements comport with each other (Van Til’s Apologetics).


This is the famous formal debate between Dr. Bahnsen and atheist promoter Dr. Gordon Stein held at the University of California (Irvine) in 1985. Hear how hard it is to deny God’s existence and how intellectually rigorous the Christian position really is.

Here is Part 1:


Here is Part 2:


Here is the transcript of the debate: Bahnsen-Stein_Transcript