Dr. Greg Bahnsen was one of the greatest Christian apologists of the twentieth century. He adhered to an apologetics method known as “presuppositional apologetics.” This apologetic method was formulated by theologians such as Cornelius Van Til, and seeks to expose the presuppositions of the atheist or unbeliever. It is based off of verses such as Romans 1:18-23, Proverbs 1:7, Psalm 14:1, John 14:6, and others. Pressupositionalism essentially states that without the Christian God, your worldview is reduced to absurdity.
The following notes are based off a lecture given by Dr. Bahnsen on how to evangelize to atheists and unbelievers using the presuppositional method. He provides four points that the Christian must look for when engaging with an unbeliever: prejudicial conjecture, un-argued philosophical bias, dialectical tension, and the inability of the unbeliever to provide for the preconditions of intelligibility.
When talking to unbelievers, 80% of what they say will be prejudicial conjecture. This is simply opinion or arbitrary statements. An example of this would be an unbeliever saying that, “The Bible is a bunch of fairytales” without providing evidence why it is false. Christians must point out that statements like this are not factual, but mere opinions.
The second point Christians must look for in apologetic discussions is un-argued philosophical bias. Un-argued philosophical bias is a fancy term meaning that the beliefs one has have not been proven to be true, but rather are assumed as true. For example, an unbeliever may say, “Jesus didn’t walk on water because people don’t walk on water.” The un-argued philosophical bias here is that miracles are impossible. However, the unbeliever has not proven that miracles are impossible. In order for them to be able to, they would have to have almost all knowledge to show that there are no exceptions to any natural laws anywhere. And, of course, since God is the Lawgiver of these laws, He may choose to intervene and break them to make His presence known.
Third, the Christian must expose the unbeliever’s dialectical tension, or show the incoherency of the unbeliever’s philosophical bias. For example, when witnessing to a naturalist (someone who thinks only the natural world exists) you could point out that they are assuming that people have free will when their worldview doesn’t allow for it. In naturalism, free will is a type of “allusion” since our decisions are determined by the laws of biology, chemistry, and physics acting on us. Therefore, you should not tell people to do things if they have no choice in the matter. The naturalist is borrowing from the Christian worldview, which states that humans have free will, when they assume others can make a free choice.
Lastly, Christians must point to the failure of the unbeliever to provide for the preconditions of intelligibility. Apologists must show how the unbeliever’s worldview cannot account for the basis of logic, reasoning, morals, and science. Then, they must demonstrate how when they utilize these principles, they are borrowing from the Christian worldview. For example, when an atheist uses moral language such as “You shouldn’t do that,” “Stealing is evil,” he is borrowing from the Christian worldview. Atheism provides no objective standard for morality, but Christianity does. Morality is based on God’s unchanging nature. Since we are made in God’s image and are not evolved cell scum, all humans know when they act contrary to God’s nature because of their God-given conscience. Another example of this would be the laws of logic. Everyone uses laws of logic, otherwise nothing would make sense. Logic is not a human construct, because A=A even if there are no humans. Logic reflects the mind of God. Thus, atheism can’t account for even the most basic philosophical principles.
Now what about other world religions and philosophies? You should still use these four principles when engaging with any unbeliever, but also bring in the authority of God’s Word. With the Mormon or Jehovah’s Witness, demonstrate how the Bible contradicts thier cultic doctrines. With Muslims, show how Muhammad’s revelations are contrary to both the Old and New Testaments. If you are dealing with someone of a Near Eastern religion, point out how their worldviews are illogical and cannot account for the preconditions of intelligibility.
If the Christian follows these four principles, they will have a much easier and more effective witnessing encounter with the unbeliever. When in doubt, remember that Christianity is the only worldview that is true and makes sense of the world. Like any method, presuppositional apologetics and evangelism takes practice. But fear not! Jesus will be with you always and the Holy Spirit will guide you (Matt 28:20, Luke 12:12).
Here is the lecture by Dr. Bahnsen that these notes are based off of.