Presuppositional apologetics is an internal analysis of worldviews. The goal is to show the Christian worldview is consistent, while the non-Christian worldview is inconsistent.
Presuppositional apologetics is an approach to defending the Christian faith that analyzes a person's presuppositions, or worldview. Everyone has presuppositions -- ideas or assumptions they take for granted. Worldviews can be defined as the fundamental perspectives through which we perceive and interpret reality. Worldviews encompass our beliefs, values and assumptions. Our worldview influences our thoughts, emotions, behaviors, and decision-making processes.
The starting point for presuppositional apologetics is acknowledging the Bible as God's inerrant Word, and hence the authoritative standard by which all truth claims are evaluated. The Bible is the ultimate standard of truth on any matter on which it touches. The two goals of presuppositional apologetics are first, to internally analyze the Christian worldview and show how it is consistent. Secondly, to internally analyze the non-Christian's worldview and show how it is contradictory or inconsistent. To avoid straw-man fallacies (false assumptions) a worldview must be analyzed internally, by the person holding it, and not from the outside.
Presuppositional apologetics makes a defense for the Christian faith by showing that a biblical worldview allows one to make better sense of the world than other, non-biblical worldviews (or presuppositions). In this sense, the presuppositional approach differs significantly from the classical and evidential approaches to Christian apologetics, which take a more "first principles" approach to demonstrating the superiority of Christian faith. Another way of saying this would be that, whereas classical and evidential apologetics focus on demonstrating the truth of Christianity, presuppositional apologetics focuses on demonstrating the internal consistency of Christianity. And of course, all three approaches do ultimately encourage belief in orthodox Christian teaching. Overall, we must be able to defend our faith with gentleness and respect, speaking the truth in love, and with a life that matches what we say we believe. The defense of the Christian faith starts with our heart attitude. What we preach must be lived out in our lives.