Today I want to talk about a logical fallacy called false dichotomy or false dilemma, I will be drawing a bit from Wikipedia and iron chariots. I have been thinking about doing blog posts for various logical fallacies for a while, and this particular one came up a number of times this week when I was reading the problem of pain.
Before we talk about what a false dichotomy is, let me simply state what a dichotomy is. In the context that is relevant to us, a dichotomy is a situation where there are exactly 2 possibilities where there is no overlap. There are 2 conditions, say A and B, such that you have to have either A or B and you can't have both. An example of a dichotomy is my lights are either on or off, those are all of the possibilities, the light is either on or off and it can't be both on and off at the same time.
An example of something that is not a dichotomy is my glass of water is either full or empty, it does satisfy that you can't have both at the same time (clearly a glass of water can't be both full and empty at the same time) but full and empty aren't the only possibilities, it is possible for a glass to be neither full nor empty, there are other possibilities such as half full. A true dichotomy of the glass would have to be something like empty or non-empty instead of empty and full.
So now that we know what a dichotomy is, let's talk about false dichotomy, this is when it is claimed that there are only 2 possibilities that cover everything when in actuality there are alternatives. As far as I have seen, the common use of this is someone will claim that there are only possibilities A and B when there is really another possibility C. The person arguing will then show (or claim) that A is impossible and conclude that B must be true, but they never addressed the alternative C. That is really all there is to it, let's look at some examples.
We already have one example with the glass. Suppose I were to claim that the glass has to be either empty or full, if you believed me that those are the only 2 possibilities and I could show that there is some water in the glass you would have to conclude that the glass was full, which is absurd. Similarly, if I could show you that the glass was not completely full (if I could stick my finger into the top of the glass without getting water on it for example) then the glass must be empty, equally absurd. This example is obviously ridiculous, but the point is if you start with a flawed assumption you can use it to prove absurdities.
Back to the problem of pain, near the end of the first chapter Lewis says the following "Either [Jesus] was a raving lunatic of an unusually abominable type, or else He was; and is; precisely what He said." Both of lewis' possibilities have Jesus being truthful, it's just that in one he is correct and in the other he is wrong. What if he is lying or being deceptive? That is certainly a possibility.
Shortly thereafter Lewis says the following (he referring to a typical person) "He can refuse to identify the Numinous with the righteous, and remain a barbarian, worshiping sexuality, or the dead, or the life-force, or the future." Do I really need to explain why this is crap? He is saying you need to 'identify the numinous with the righteous' which basically means you need to think God is good. If you don't think God is good you absolutely must be a barbarian or worship sexuality, the dead, the life-force, or the future. There are plenty of people in the world who don't worship anything and they are not barbarians.
One more, he says the following in the same paragraph as the above "He can close his spiritual eyes against the Numinous, if he is prepared to part company...with the richness and depth of uninhibited experience." Here he is saying if you believe in the numinous (spirits and such) then you can have deep uninhibited experiences, if you don't believe in the numinous, then you cannot. I honestly don't see what one thing has to do with the other. If anything I might argue that religion makes you more inhibited, that certainly seems to be the picture Lewis is portraying when he says these people worship sex.
I hope my examples from the problem of pain demonstrate how the fallacy works. I wanted to add one more thing, a warning sign that this technique is being employed is that since the alternative is false, my way must be true. If it seems that someone is arguing against an opponent instead of arguing for their own point, it is quite likely they are using this fallacy.