Some of the most interesting things to study when it comes to logic are the arguments for the existence of God. They come in all shapes and sizes. There is the Ontological Argument, which argues from the very idea of God to His real existence. There is the Cosmological Argument, which argues from the fact that everything in the world is dependent upon something else for its existence to the fact of a being who makes sense of it all. And there is also the Teleological Argument, the Moral Argument, and others.
But there are other arguments that never make it into the pantheon of the so-called “classic” arguments for God’s existence, even though they are just as interesting and, some of us would say, just as effective logically.
One of these is C. S. Lewis‘ so-called “Trilemma,” or “Lord, liar, lunatic” argument. This argument is not a straightforward argument for the existence of God. It approaches the issue of God’s existence indirectly.
The argument appears in Lewis’ Mere Christianity. Lewis introduces the argument by observing how most people who don’t believe that Jesus is God are still attracted to Him as a moral teacher. While He is not God, these people say, He was a great moral teacher.
Lewis presents the argument as a sort of minor digression, a throw off. Here it is, in one paragraph:
I am 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 the 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. You can shut Him up for a fool, you can spit at Him and kill Him as a demon; or you can fall at His feet and call Him Lord and God, but let us not come with any patronizing nonsense about His being a great human teacher. He has not left that open to us. He did not intend to …. Now it seems to me obvious that He was neither a lunatic nor a fiend: and consequently, however strange or terrifying or unlikely it may seem, I have to accept the view that He was and is God.
Stated a little more formally, the argument goes like this:
Jesus claimed to be God. His claim is either true or false. If it is true, then, ipso facto, He is God. If the claim is false, then either He said it knowing it was false, in which case He is a liar, or He said it not knowing it was false, in which case He was mad. Therefore, we are left with three logical options: He is either God, or a liar, or a lunatic.
To say Jesus was a liar will seem quite a stretch for most people (even unbelievers), particularly if they think He was a great moral teacher. A great moral teacher would not, by definition, lie, and certainly not tell a lie of such magnitude as to claim to be God when He wasn’t.
To say Jesus was a lunatic is also a stretch, since His teaching would appear to be the quintessence of sanity—and, of course, a great moral teacher is, again by definition, sane.
So if He was not a liar and not a lunatic, the only other logically possible conclusion is that He is God.
Notice that, among the three logical possibilities, great human moral teacher is not one of them. That Jesus was merely a great human moral teacher is, literally, not logically possible.
It is, though, logically possible to hold that Jesus was dishonest or insane. But for the vast majority of people these are just not acceptable options. This argument doesn’t logically force anyone to accept that Jesus is God, but its logic forces those who don’t want to believe He is God to reject the idea that He was a great moral teacher. Lewis constructs the argument in such a way as to either force atheists to accept Jesus is Lord, or to accept that this moral teacher is either mad or mendacious, insane or insidious, demented or duplicitous.
An unbeliever must say, well, then Jesus must be either mad or a liar. But it won’t sit easy with him.
It is important to note that, although the argument is called “Trilemma,” such a title is a little misleading. It seems to suggest that the argument is just a dilemma, an argument with two lemmas (two propositions used to prove other propositions), with an additional lemma.
A dilemma looks like this:
If P, then Q; and if R, then S
Either P or R
Therefore, either Q or S
This is not strictly the structure of the Trilemma. The structure of the Trilemma is more like this:
Either P or Q or R
Not Q or R
P being Jesus is God, Q that He was a madman, and R that He was insane. The Trilemma is really a disjunctive syllogism with three disjuncts (P, Q, and R).
However, what this Trijunctive argument does is put the unbeliever in a dilemma:
If Jesus claims to be God and the claim is true, then He is God; and if He claims to be God and the claim is false, then He was a liar or a lunatic
Either His claim is true or false
Therefore, either Jesus is God, or He was a liar or a lunatic.
Does the Trilemma logically prove God’s existence? No. But what it does is to cancel out the possibility that Jesus was simply a great moral teacher, and put the person who denies His deity in a dilemma from which there is no easy escape.