- Jesus was either a liar, a lunatic, or God.
- Jesus was not a liar or a lunatic.
- Therefore, Jesus was God.
Liar and Lunatic
I'll tackle the second premise first. Lewis hugely exaggerates the implications of Jesus being mistaken or making a false claim to divinity. In these two cases, Lewis says in Mere Christianity, Jesus is either "on the level with the man who says he is a poached egg—or else he would be the Devil of Hell."
|Mmm, poached egg...|
and on toast, no less.
Then comes the "liar" prong of the Trilemma. Would falsely claiming to be God necessarily make someone on par with "the Devil of Hell," as Lewis claims? Certainly not. For example, perhaps Jesus was a great moral teacher, but told a single lie in the hope that it would help spread his moral teachings far and wide. Doing a little evil to achieve a much greater good seems like a perfectly plausible rationalization for a moral teacher to make. And even if this lie did imply that Jesus was evil, so what? Maybe his teachings were a charade put on for the purpose of gaining widespread fame, in the style of some modern televangelists. These scenarios may not be likely, but they're much more probable than the "God" conclusion, and they demonstrate why the blanket assumptions made in the Trilemma are problematic.
The Other Options
The first premise is even flimsier than the second. There is no reason to limit one's options to Lord, liar and lunatic. We can instead question the entire basis of the claims, and even consider the possibility that Jesus never existed at all (a topic that I plan to do more research on in the future). We'll call this the "fabrication" view. To be sure, most historians think he existed. But due to the startling lack of reliable evidence both inside and outside the Bible, there seems to be a small but nevertheless very real chance that this theory is correct.
And then we have the view that a man named Jesus existed, but never claimed to be God—the divinity claims found in the Bible were invented by later writers. We'll call this the "legend" view. This is the actual position of many New Testament scholars today. Some believe that he only thought of himself as an agent of God, or a kind of apocalyptic prophet warning the world of impending judgment. Once we drop the unnecessary and question-begging assumption that the gospels provide an accurate portrayal of Jesus, the Trilemma completely falls apart.
In the first section I showed that the two prongs of the Trilemma that Lewis wants us to deny are actually fairly plausible. In the second, I added two more prongs to create a "Pentalemma." Now we must choose between liar, lunatic, legend, fabrication, or God—and any of the first four labels are more likely to describe Jesus than the latter one. In light of the current Biblical scholarship, the legend viewpoint seems most probable.
Lewis' Trilemma is flawed on multiple levels: it takes the reliability of the gospels for granted, it throws out two valid options, and it completely ignores the other options available to us. In a way I hope that apologists continue to use this argument, because it's so transparently awful that it should instantly make people skeptical of any other claims that they make.