As I mentioned in part one of this article, C.S. Lewis used abductive reasoning to argue that the Christian explanation of reality — the Christian worldview — is more reasonable and probable than the alternatives. (Recall that abductive reasoning is similar to reasoning used by scientists in that it uses reasonable evidence to come to the best explanation.)
Now I'll take a closer look at two of Lewis' key arguments that use abductive reasoning:
Jesus once asked his disciples, "Who do people say I am?" After hearing a few replies, he put forth a more pointed and personal question: "'But what about you?' he asked. 'Who do you say I am?'" (Mark 8:27-29).
In exploring the alternatives regarding the claims of Christ, Lewis used abductive reasoning to conclude that the most probable explanation is that Jesus is who He said He was. In Mere Christianity, Lewis provides a brief presentation of his argument: "I'm trying here to prevent anyone saying the really foolish thing that people often say about Him: 'I'm ready to accept Jesus as a great moral teacher, but I don't accept His claim to be God.' That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic — on the level with a man who says he is a poached egg — or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God: or else a madman or something worse." 1
Beyond some biblical hints at such reasoning (John 8:48-49 and John 10:33), the core of this argument goes back to Eusebius of Caesarea (c. 263-339), who outlined it in Demonstratio Evangelica ("Proof of the Gospel"). Lewis popularized the argument in Mere Christianity. Since then, several apologists have expanded it to include other alternatives beyond the traditional "Lord, Liar, or Lunatic?" options. 2Based on the evidence and the truth of the Bible, these apologists, like Lewis, conclude that the most reasonable explanation is that Jesus is who He claimed to be.
Another line of reasoning Lewis used is called the argument from longing or desire. In it, he not only makes the case for God, but also the case for heaven.
Lewis believed that everyone experiences sensations of desire and longing. We may spend a lifetime trying to fulfill these desires by pursuing earthly pleasures such as taking vacations, moving from one sexual partner to another, or trying different hobbies — "always thinking that the latest is 'The Real Thing' at last — yet always ending up disappointed."
Our experience tells us, Lewis continues, that "Creatures are not born with desires unless satisfaction for those desires exists. A baby feels hunger: well, there is such a thing as food. A duckling wants to swim: well, there is such a thing as water. Men feel sexual desire: well, there is such a thing as sex." 3
How, then, can we explain deep inner longings that we have that nothing in this world seems to satisfy? Of course, it would make sense to begin by demonstrating that human beings do indeed have these longings. Some might argue that not everyone does have these desires or that they really do not point to God. Lewis disagreed, though, arguing that our longings for the 'other' — even though they may manifest themselves in different ways, such as material pursuits — are really longings for the transcendent joy that is found in God alone. 4
The fact that we have this longing, combined with the fact that nothing on earth can truly satisfy it, led Lewis to this reasonable conclusion: "If I find in myself a desire which no experience in this world can satisfy, the most probable explanation is that I was made for another world." 5
In The Lion, the Witch and the Wardrobe, the professor concludes that a little girl named Lucy is telling the truth about her claims to have visited a world called Narnia. He does this by using abductive reasoning. The professor rationally explores the alternative explanations and concludes that they are unlikely. "For the moment then and unless any further evidence turns up," argues the professor, "we must assume that she is telling the truth." 6
In making the case for Christianity, we, too, can use logic such as abductive reasoning. If we can provide arguments and evidence that Christianity is more reasonable and probable than other explanations of reality, then it is rational to conclude — "for the moment and unless any further evidence turns up" — that Christianity is, as the apostle Paul said, "true and reasonable" (Acts 26:25). 7