Science and Other Drugs

….maybe a little less wrong….

Logical Fallacies: The argument from silence

One of the principal reasons I moved away from fundamentalism was the overwhelming presence of fallacies. As a good Fundamentalist Homeschooler, I was taught to hunt down and identify fallacies as efficiently and ruthlessly as the heat-seeking missile shown below.

The AIM-9 Sidewinder missile uses an infrared heat-seeking module and a warhead that expands into a jagged spinning ring of metal death on impact. Image courtesy USAF.

Unfortunately, fundamentalism is home to some pretty egregious fallacies in its own right, ones that became rapidly apparent as I turned my abilities back on my own indoctrinated beliefs. Wait, why do we believe such-and-such? No good reason at all? Interesting.

And so we come to today’s fallacy: the Argument From Silence.

This post was prompted in part by the following comment over on Ark’s blog, where I found myself embroiled in a frighteningly controversial debate…if it could be called that.

The Romans were rather enthusiastic record keepers. We can find the names of the favorite wines, slaves and concubines of many third-level leaders of the Roman empire, but they didn’t bother to provide numerous references to this Jesus-fellow, allegedly a notorious troublemaker in their most troubled province? Ancient history happens to be one of the areas of my expertise, and all I have to say is: You have got to be kidding!

Officially, the argument from silence is a fallacy. But, surprisingly, it doesn’t have to be. An argument from silence can be entirely valid, provided it is presented in the right way.

There are two ways an argument from silence can go. I’ll start with the more common one—at least, the one more commonly seen in heated debates:

“If a particular piece of evidence existed, it would prove a certain point. That piece of evidence doesn’t exist, so that point must be false.”

In terms of semi-formal logic, it looks like this:

If P, S
∴ Not-S

An example might be a common creationist argument: “Where are the transitional fossils? We don’t have fossils showing creatures with both lungs and gills. So land animals must not have evolved from fish.”

Another more egregious example: “God never said gay marriage was okay, so it must be wrong.”

It’s easy to see why this is invalid. Just because a particular “if” statement is false doesn’t mean its corresponding “then” statement is false as well. If I call my wife to tell her I’m coming home for dinner, she knows I am….but just because I forget to call doesn’t mean I’m suddenly never going to return.

Even so, the argument from silence has an uncanny intuitive appeal. It’s a method of advancing suspicion; we wonder why that particular piece of evidence is missing. As it turns out, this is where the valid version of the argument from silence comes in.

Let’s go back to the original comment above that spawned this whole post (paraphrased). “The Romans kept records of a lot of stuff, but they didn’t mention Jesus, so Jesus must not have existed (or at least not as the Gospels depict).” The problem here is obvious: just because the Romans didn’t mention someone doesn’t mean they didn’t exist. There’s no mention of Paul in Roman records (to my knowledge), but no one seriously advances the theory that Paul didn’t exist. No sources (Roman or otherwise) mention the father of Pilate, but you don’t see anyone thereby concluding that Pilate was born of a virgin.

But the argument can be salvaged. Instead of saying:

If the Romans mentioned Jesus, he existed.
The Romans didn’t mention Jesus.
Therefore, Jesus didn’t exist.

we reverse the order of the major premise:

If Jesus existed, the Romans should have mentioned him.
The Romans didn’t mention Jesus.
Therefore, Jesus didn’t exist.

And, before your very eyes, we now have a valid syllogism! Just like magic.

This actually IS a valid syllogism:

If S, P
∴ Not-S

But our work isn’t done. Not yet. Making an argument from silence valid produces a new premise that has to be evaluated. In this case: “If Jesus really existed (as the gospels depict), should we expect the Romans to have mentioned him?” And that question can actually be studied and discussed; it’s an opportunity for further inquiry instead of just an unquestionable endpoint. That’s another good way to tell fundamentalism and bad logic apart from good reasoning. Good arguments invite examination; bad arguments silence it.

With a little work, it’s easy to figure out what questions need to be asked about the first two examples I gave. Just reverse the major premise and turn it into a question. To the creationist, you ask, “If land animals did evolve from fish, would we expect to see a fossil with both gills and lungs? Why, where, and how frequently?” To the traditional-marriage apologist, you ask, “If gay marriage is okay, should we expect the Bible to say something about it? When? What book and what chapter? Where would it have been a relevant statement at the time the Bible was written?”

When it came to the former comment from Ark’s blog, the complete question ended up being fairly simple: “If Jesus existed, should we really have expected the Romans to write about him in documents we currently have copies of? Which real-life surviving manuscripts should have mentioned Jesus but don’t?”

Easy. Of course, actually getting people to defend their premises might prove a tad more difficult. Especially if they aren’t used to doing so.


19 responses to “Logical Fallacies: The argument from silence

  1. Arkenaten 2013/04/13 at 18:47

    “Let’s go back to the original comment that spawned this whole post.
    ”The Romans kept records of a lot of stuff, but they didn’t mention Jesus, so Jesus must not have existed (or at least not as the Gospels depict).”
    Where in any part of my post or the comments does this line of dialogue appear?

    • physicsandwhiskey 2013/04/13 at 18:54

      That’s a paraphrase of the block quoted comment at the beginning of the post.

    • violetwisp 2013/04/14 at 10:14

      Hi Arky! Did you follow any of that? Do you not feel even slightly motivated to defend your point? Come on, just for fun between good blogging buddies!! “If Jesus existed, should we really have expected the Romans to write about him in documents we currently have copies of? Which real-life surviving manuscripts should have mentioned Jesus but don’t?” I’m waiting ….

      • physicsandwhiskey 2013/04/14 at 10:16

        Well, to be fair, it was TS’s comment, not his.

      • violetwisp 2013/04/14 at 10:18

        It’s still his post and it was a point he agreed with.

      • Arkenaten 2013/04/14 at 11:26

        LOL…you just want to see me bleed. I’m actually disappointed old Pontius Pilot didn’t have commemorative tea mugs made, or Barabbas-patterned Togas. Bloody Romans; at times,they had no sense of narrative convenience.
        Still, didn’t Constantine’s mum find the original cross they nailed poor old JC to?
        I believe the ”whole original cross” could at one time be found in at least three churches across the Levant,or so I heard, and no doubt she probably took another original back home …as a souvenir, of course.
        But there may may be one more post on this Nazareth issue…This one might cast aspersions on none other than the real founder of the Christian religion, but we’ll see how adventurous I am feeling.
        Only for the extremely thick-skinned, intellectually open-minded dickheads and truly snarky Argentinians.

      • physicsandwhiskey 2013/04/14 at 11:35

        I have no concerns about what names you call me, but I’ll thank you to leave off insulting my readers. At least here.

        Pilate clearly had no concept of merchandising.

  2. Arkenaten 2013/04/13 at 19:03

    Your mummy must be so proud!

  3. Arkenaten 2013/04/14 at 11:39

    Edit as you see fit…

  4. Arkenaten 2013/04/15 at 05:16

    Right up your street, I should think.

    “Thank you, Ark”
    “Your welcome…”

  5. Mark Hamilton 2013/04/23 at 00:21

    Yeah, I’ve never liked the transitional fossil argument myself, and I’m still a YEC! It mean, alright, maybe a lack of transtional fossils (though whether a fossil is transitional is not is mostly a matter of interpetation) means evolution might be a little less likely, but it’s no smoking gun proof there. Always bugs me when people trot that out at a central argument when it should be a tertiary one at best.

  6. Pingback: Red Flags Of Quackery | Illuminutti

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