The field of Christian apologetics entails three major approaches. Classical apologetics, which employs a deductive argument in its apologetic method. Evidential apologetics, which employs an inductive argument in its apologetic method. And presuppositional apologetics (PA), which employs a transcendental argument in its apologetic method. Of the three, PA can be the most challenging to understand. But I believe that if the thinking Christian will take the time and spend the energy to understand PA, the dividends will be more than worth it.
As was stated above, PA employs a transcendental argument in its defense of the faith. You will very often see this argument referenced with the acronym TAG: The Transcendental Argument for God. A transcendental argument (TA) seeks to demonstrate the necessary preconditions for a particular state of affairs, and in this case, for all human predication. A TA takes on (roughly) the following form: For x to be the case, y must also be the case because y is the necessary precondition of x; since x is the case, y must be the case. PA employs this method of argumentation to demonstrate that Christianity is true.
For human predication to be the case, God must be the case since God is the necessary precondition for human prediction. Since human predication is the case, God must be the case. This is the basic shape of TAG. After all, one cannot deny human predication without engaging in human predication. In additional to this, PA presupposes and strongly emphasizes the epistemic authority of Scripture. This claim based on the clear teachings of Scripture about itself. So then, it follows that the God that PA contends exists, and is the necessary precondition of human predication, isn’t just any god, or some divine transcendent supernatural being. Such a conclusion is repudiated by PA not only as inconsistent, but as being unfaithful to the biblical text and the clear teachings of Christianity. Rather, the God who is the necessary precondition of the intelligibility of human experience is the God proclaimed and taught in Christian theism.
Cornelius Van Til rightly points out in his book on apologetics, “We must first ask what kind of a God Christianity believes in before we can really ask with intelligence whether such a God exists.” Since God is a transcendent being, it is necessary that he reveal himself to humanity. And in this revelation, we can know something about the kind of God that exists. According to Christian theism, God has revealed himself in nature, and more accurately in the Christian Scripture, what we call, the Bible.
PA begins with the Bible as its epistemic authority and proceeds from there. This is in direct contrast with the deductive (classical) or the inductive (evidentialist) approaches. The differences in the three approaches are epistemological in nature with metaphysical overtones to be sure. While classical and evidential approaches rely on rationalism and empiricism respectively, the presuppositional method emphasizes revelation as its epistemological starting- point. For this reason, there is a strong emphasis in PA on Christian theology. Not only is theology proper strongly emphasized, but so too are anthropology (doctrine of man), hamartiology (doctrine of sin), and the doctrine of Scripture. To be sure, PA sits upon the foundation of a strongly reformed theology of Christianity.
Presuppositional apologetics recognizes the antithesis that exists between Christian and non-Christian thought. It is not the sort of antithesis that arguments or evidence is capable of removing. The antithesis exists at the level of worldviews, at the very basic level of presuppositions or basic beliefs. For this reason, PA argues at the level of worldviews. The question PA asks is, “What are the necessary preconditions for the claims of x worldview?” The strategy is to place the claims of the non-Christian worldview under the scrutiny of its own claims to see if it can demonstrate internal consistency and coherence.
For example, one can turn to a famous claim of a famous atheist and see how PA would respond. “The God of the Old Testament is arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser; a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully.” Richard Dawkins is an atheist and as such denies that human beings were created or designed for any purpose whatsoever. Humans are simply by-products of natural processes, a freak of nature, if you will. PA will place the following demand on Dawkins: given your basic belief that human beings are essentially highly evolved slime, without significance or meaning, or purpose in life, what rational basis are you able to provide for your obvious claim of the existence of objective morality.
In order for Dawkins’ belief about God to be the case, objective morality must be the case. But in a world of natural processes, where human lives are no different than the life of an insect, no more valuable than the life of an ant, then it seems quite impossible for objective morality to be the case. And if that is true, Dawkins’ moral judgment where God is concerned has absolutely no rational basis whatsoever.
Presuppositional apologetics then takes a two-tiered approach. First, we step into the shoes of someone like a Richard Dawkins and ask them to provide a rational defense for their own worldview. One they have failed at every turn in their efforts to do so, we ask them to step into the Christian’s shoes and look at things from our vantage point to see if Christianity can do any better. And as a result, every non-Christian worldview is shown to reduce to skepticism and only the Christian worldview is left standing on the field of intellectual inquiry.
 There are less popular approaches, such as the cumulative case method which is closely related to evidential apologetics. And then there is the Fideistic approach which is not often encountered today. I limit this article to the main players for practice reasons.
 Steven M. Schlissel, The Standard Bearer: A Festschrift for Greg L. Bahnsen (Nacogdoches, TX: Covenant Media Press, 2002), 91.
 Van Til, Cornelius. The Defense of the Faith. Phillipsburg, NJ: Presbyterian and Reformed Pub. Co., 1985, 9.