Not everyone is convinced that the Lewis trilemma is useful in apologetics, but it may be good to point out that Lewis was dealing with one specific issue -- the assertion that "Jesus was a great moral teacher, but not the Son of God."
As the Wikipedia article on the Trilemma points out, the three options that define a trilemma must be mutually exclusive and jointly exhaustive. In other words, choosing one option requires that the other two be rejected as false, and the three options must cover all possibilities.
So, assuming that Jesus made claims of divinity for himself (which Scripture leads us to believe), then either he is the Son of God or he is not the Son of God. If he is not, then he is either a liar or he is delusional.
Lewis' point was that if he was not the Son of God, then being a liar or crazy would not be consistent with being a "great moral teacher". This pretty much means that the two characterizations -- Son of God; Great Moral Teacher -- must be accepted together or rejected together.
Does this prove that Jesus was the Son of God? No. All it does is remove one of the arguments against his divinity.
It seems to me that trilemmas are only good for logically eliminating possibilities. What is left is not necessarily "proven".
Let's look at another claim that might lend itself to a trilemma: Did Jesus rise from the dead or didn't he?
Some have said that the disciples concocted this story, and that it was all a lie. Others have said that the disciples were under some sort of mass delusion. The Scriptures make the claim that Jesus rose from the dead.
So, given the underlying assumption that resurrection claims were in fact made, then we are left with the following possibilties:
- The apostles lied, and in turn convinced others of the lie, and this lie resulted in the Christian religion as we know it today.
- The apostles were victims of mass delusion and convinced others of the truth of their claims.
- The apostles saw the Risen Lord, and told the Good News to all who would listen.
The second option, mass delusion, is a little trickier. Jonestown comes to mind as does the Heaven's Gate sect. Both groups committed mass suicide as a result of mass delusion. It is hard for me though, to accept mass delusion as an explanation for the spread of the resurrection story. I'd have to believe that the women at the tomb, the eleven remaining disciples (including Thomas, who had to see for himself), and others who claimed to have seen the Risen Lord were all suffering from a common delusion. The apostles were accused by some of having had "too much wine", but as Peter pointed out, "It 's only nine in the morning". (Acts 2:13-16)
Occam's Razor suggests that when two competing explanations are made for a particular event, the simpler one is preferred. Both of the above options that deny the Resurrection require assumptions that are not supported by known facts. Another "explaining away" of the Resurrection is that Jesus was taken down from the cross in a comatose state. To believe this requires that one believe that the Romans (who were very good at crucifixion) bungled this one.
If the resurrection never happened, then the crucifixion should have been the end of it. So what made the apostles, and those who heard and believed the Good News, go out into the world and preach and teach what Jesus had taught them? What made them willing to suffer death for what they believed?
To use a well-known quote from Sherlock Holmes: "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." Or, in matters of faith, becomes easier to accept as the truth.
Does this trilemma prove that the Resurrection happened? No. But it goes a certain distance toward eliminating some common objections to the idea, and coupled with what we know of the way the early Church spread over the Middle East, and into Europe, it makes the Resurrection more plausible on an intellectual level.
It still remains a matter of faith -- but the more I think it through, the shorter the leap becomes.