Presuppositional apologetics is an approach to apologetics which aims to present  a rational basis for the Christian faith and defend it against objections by  exposing the logical flaws of other worldviews and hence demonstrating that  biblical theism is the only worldview which can make consistent sense of  reality.

Presuppositional apologetics does not discount the use of  evidence, but such evidences are not used in the traditional manner—that is, an  appeal to the authority of the unbeliever’s autonomous reason. Presuppositional  apologetics holds that without a theistic worldview there is no consistent basis  upon which to assume the possibility of autonomous reason. When the materialist  attempts to refute Christianity by appeal to deductive reason, he is, in fact,  borrowing from the Christian worldview, hence being inconsistent with his stated  presuppositions.

The presuppositional approach to apologetics calls for  the Christian and non-Christian to engage in an internal examination of their  respective worldview and thus determine whether or not they are internally  consistent. The essence of presuppositional apologetics is an attempt to  demonstrate that the non-Christian’s worldview forces him to a state of  subjectivity, irrationalism, and moral anarchy.

Since the unbeliever’s  worldview is objectively false, it of necessity contains demonstrable  contradictions (e.g., he makes moral judgments, but he cannot account for moral  absolutes without the theistic worldview). The believer, within the Christian  framework, can account for things like rationality, logic, uniformity of nature,  morality, science, etc., because the Christian worldview conforms to a  transcendent reality.

In summary, the presuppositional apologist engages  in an internal critique of a given worldview in order to demonstrate that it is  arbitrary, inconsistent within itself, and lacks the preconditions for  epistemology. The presuppositional apologist can thus take a given value which  is held by the unbeliever and demonstrate to him that if his own worldview were  true, that very belief would be incoherent and/or meaningless. Presuppositional  apologetics seeks to prove Christianity with reference to the impossibility of  the contrary. In other words, unless the Christian worldview is  presupposed—whether at a conscious or subconscious level—there is no possibility  for proving anything.