RazorsKiss poses an interesting question over at Vox Apologia: "The Trilemma: Useful or Useless?"
Since this apologetic argument is (most?) often associated with C.S. Lewis, of whom I am an unabashed fan, I thought it a very good topic to tackle.
In general terms, a trilemma is a logical construct containing three options. Either something is X, Y, or Z. In the case of Christian apologetics, the trilemma states that Jesus Christ was either a liar, a lunatic or Lord. In other words, He was either who He said He was, or we shouldn't follow Him because He's insane or a liar.
So is this a useful tool in the apologist's toolbox? I will state unequivocally that it might be. Or it might not. There. Problem solved.
Well, not quite. There are a couple of main reasons I think it may not be a helpful tool, at least not at all times or places. First of all, the argument presupposes that the historicity of the Gospels are not in question. That is, to argue the trilemma assumes that Jesus did actually, historically, make these very claims. If He did not, then evaluating the trilemma becomes an interesting intellectual exercise, but really not applicable to anything real. If you wish to use the trilemma, you need to ensure the listener is already in agreement with the idea that Jesus actually made the claims described in the Gospels.
A second problem is that there may be alternatives not encapsulated by the trilemma, which turns the argument into a logical fallacy, specifically a type of"false dilemma". An example would be that Jesus was sane, but really thought He was God when He wasn't. In other words, He was wrong, but not intentionally so. I'd put this under the "liar" category, but if the listener doesn't, the argument loses its force because the listener is distracted. Regardless of whether the listener is correct in categorizing the options, the argument isn't going to be very helpful if the listener doesn't buy that these are the only three options.
The final problem is that, well, we cannot "prove" any part of the trilemma is an invalid option. We do not have psychiatrist's notes from ca. 30 A.D. demonstrating that Jesus was psychologically healthy. We don't possess hundreds of pages of Roman Senate Committee reports on the question of whether Jesus was a truth-teller. We have reasonable evidence that Jesus was sane, and that he told the truth, but it is not definitive. If it were, we'd have far fewer skeptics! For many skeptics, the suppositional nature of the trilemma is an insurmountable problem. They need more evidence to decide that He was neither liar nor lunatic, so they cannot yet concede that He is Lord.
That being said, there is some power in this argument. As Lewis used it, he was arguing against one specific claim: that Jesus was merely a good teacher. While it may be true that the trilemma says nothing definitive about Christ's deity, it at the very least points out that Jesus could not have been just a "good teacher." A good man tells the truth. It doesn't make sense to revere Jesus as "a good man who taught some good things" if any but the "Lord" option in the trilemma is held to be the case.
The argument could also be useful in bringing an unbeliever to the point of realizing he or she has to make a decision on Christ, as long as it is used with other apologetic evidences. That is, if the apologist has brought the unbeliever to the point of acknowledging the Bible is historically reliable, or at least that it is reasonable to believe it is, then this argument can bring the unbeliever to a point where they have to accept or reject the next plot point in the story.
Finally, for the believer, it is useful in our self-evaluation. It forces us to examine our beliefs to determine if we're really following a liar or lunatic, or if we're following our Lord. Anything which makes us think more deeply on who Jesus really is has a great deal of value. And for that alone, if for nothing else, we should keep this particular trilemma in the toolbox.