Careful with the Argument from Ignorance

I’m in a group that encourages honest, respectful conversations about what people believe to be true and why.

My latest conversation, with Mike, is providing a great lesson in what is called the argumentum ad ignorantiam or argument from ignorance fallacy. It relies on there being a lack of contrary evidence.

The fallacy basically goes something like this: something must be true if it has never been proven false.

Mike started the conversation by saying:

I believe that philosophical naturalism is false.

This should already raise a couple of flags.

One is this phrase, “philosophical naturalism.” So first I got clarification from Mike on what he meant by that. His answer was that for him, philosophical naturalism is the belief that the natural world is all there is.

Second, he is saying that he has a belief that another belief is false. We’re already getting into “negative” territory. After some prodding, I suggested that we should be talking about his belief that the supernatural world exists, rather than his issue with the claim that the natural world is all there is. But he was a bit unwilling to commit to an affirmative claim here so after a bit of back and forth, I’ve left him with this comment:


I’m still not entirely sure about your process for arriving at the belief that naturalism is false. I don’t want to put words in your mouth here, but let me try to rephrase where we are at, and you let me know if I’ve got it right.

1. You have a belief that the “belief that the natural world is all there is,” isn’t true.
2. That language is a bit convoluted, since we’re not really talking about something you believe to be true, but rather, something you disbelieve.
3. So let me rephrase a bit. You disbelieve the natural world is all there is, because no one has ever proven that the natural world is all there is.
4. Which is another way of saying you believe that the supernatural world must exist. And since the supernatural world has never been proven not to exist, you believe that naturalism can’t be true.

I’ve never been a big fan of saying something is true, because it has never been proven false. I like to say that something is true, because we have good reasons to believe it to be true. Conversely, I like to say that one explanation is likely false, because we have good reasons to be believe that another explanation is true.

So I think we can go one of two ways here:
a) Using Street Epistemology, you can try convincing me that my belief that the natural world is all there is, might not be based on good methods or
b) Using Street Epistemology, I can try convincing you that your belief that the supernatural exists, might not be based on good methods.

Does that sound reasonable?


That’s where we are at the moment. So stay tuned.

Beware the slothful induction


If ever there was a logical fallacy which seemed to epitomize intellectual dishonesty, it is slothful induction.

Slothful induction, sometimes called “ignoring the evidence,” is the fallacy whereby an inductive argument is denied its proper conclusion, despite strong evidence for the inference.  If that still doesn’t quite make sense, allow me to explain.

First, what is an inductive argument?  Simply stated, an inductive argument is one made from the available facts. In other words, like a detective at a crime scene gathering clues about the crime, an inductive argument builds to a conclusion by piecing together the details, the evidence, that support it.  It’s the “most likely” conclusion – or inference –  based on what has been collected, observed, tested, measured, and analyzed.

One exhibiting slothful induction, either willfully or through an absence of aptitude, refuses to accept what is most likely true despite the evidence presented.  It is a forgiving name in that this fallacy gives the benefit of the doubt to the denier, by chalking up their unwillingness to acknowledge evidence to their laziness, not their confirmation bias.

However, more often than not, the denier committing this fallacy is not lazy, but rather simply does not like the direction the evidence is heading.  She chooses to ignore it.  I sometimes call this the “head in the sand” defense or to use more colorful language, the “head up one’s own ass” defense.

A very good essay discussing the slothful induction fallacy can be found at The Illogic Primer.  Within that essay, there is a key phrase that I want to point out,

“Usually it (slothful induction) is a red flag that someone is not principally interested in the truth of a matter. And, because inductive arguments are at best probabilistic, not definitive, someone can always hold out against the preponderance of evidence.”

So if you find yourself in a debate where the evidence you are presenting is being ignored, what is your recourse?  You have very little to be honest.  You are in a debate with an individual who does not value evidence and reason, therefore you will not be able to use evidence and reason to influence the argument.

In the words of the great philosopher/poet Kenny Rogers, you have know when to hold ’em, know when to fold ’em, know when to walk away, and know when to run.  When faced with slothful induction, sometimes your only option is to walk away (or run).

No ad hominems you big dummy!

As elementary school students, we very likely, in a fit of playground rage, shouted a derogatory name at one of our classmates. Perhaps someone had just purposefully blasted our four-square ball to the other side of the street or maybe someone had just said that his dad was tougher than your dad.  Either way, we didn’t want to get sent to the principal’s office for fighting, so calling this person a name was the only recourse we felt we had in our state of paralyzed impotence. We wanted to make sure that we sent a clear message, so being young and unable to form a cogent argument, we exploded with the best our young minds could muster at the time.  “Oh yeah, you’re a big fat stupid head!”

In so doing, we committed our first logical fallacy, the ad hominem.

It is at its core a fallacy of irrelevance. In other words, it is a type of argument that even when true, doesn’t address the premise.  It is an attack of the person rather than of the position.  The argument bypasses substance and evidence and instead attacks characteristics of the opposition such as their appearance, their personality, what job they might have, their accent, their sexual preference, their race, their age, and so on.

And even among adults, sometimes the ad hominem is just old-fashioned playground name-calling.  Take the following fictional gun control debate:

Pro gun control: Guns kill people and need to be regulated.

Anti gun control: People kill people and gun ownership is a guaranteed right under the US Constitution.

Pro gun control: I would expect nothing less from a right-wing nut job.

Anti gun control: I would expect nothing less from a bed-wetting liberal.

And there it ends. Two ad hominem fallacies lobbed at each other, neither of which have moved either party closer to anything remotely resembling substance.

But ad hominem fallacies aren’t always as straightforward as playground name-calling. Sometimes attempts to discredit an argument by attacking the person are more nuanced and quite frankly, more “effective” in that they subtly link the person to a position that implies bias.  It is a common trap, therefore it is incumbent upon the clever critical thinker to recognize when this tactic is employed. Caveat emptor.

What follows is an example of this tactic from my own experience. In this case, the ad hominem was intended to cast doubt on my proposition by attacking the circumstances of my job.  I was discussing the importance of vaccinations with a friend of mine, who as it turned out, is an anti-vaxxer:

Me: Vaccines are highly effective at preventing many types of childhood diseases, such as measles, mumps, and whopping cough.

Anti-vaxxer: You worked at the Centers for Disease Control therefore you’re just regurgitating big pharma lies.

Me: My work at the CDC is irrelevant to the point.  I could be unemployed and that wouldn’t change the fact that scientific and medical evidence overwhelmingly illustrates the effectiveness of vaccines.

Anti-vaxxer: *promptly conceded the point and dashed out to get her child immunized*

If only the anti-vaccine argument ended that quickly and that successfully. That said, notice that rather than attacking my proposition by presenting evidence that would contradict it, the anti-vaxxer attacked my work history with the intention of casting doubt on my credibility – in this case by suggesting that my objectivity was compromised by my relationship with the CDC.

Also notice that part of the ad hominem in this case was actually true; that is, I did in fact work at the CDC.  As I stated in my retort however, the fact of my relationship to the CDC was irrelevant to my proposition.  After all, I understood the efficacy of childhood immunizations long before I started working at the CDC. What is relevant to my proposition with regards to the CDC, is published data regarding the public health successes of childhood immunizations, such as the data illustrated in the below graphic. But anti-vaxxers have no countervailing data to support their claims, therefore ad hominem is one of their only options.


Finally, not every charge of argumentum ad hominem is actually ad hominem.  Some people will claim they are victims of ad hominem arguments, when the arguments are in fact relevant.  In my previous example, I was calling my interlocutor an anti-vaxxer not to be mean, but rather because they are actually against vaccinations. This can be a particularly frustrating situation for someone trying to have an intellectually honest conversation. Take the following hypothetical example:

Person A: Did you see my Facebook post about those 2 million year old hominid fossils recently discovered in Ethiopia?

Person B: I don’t read lies concocted by science to trick us in to believing the earth is older than 6000 years.

Person A: Wow, I didn’t realize you were a young earth creationist.

Person B: Typical evolutionist resorting to ad hominem attacks!

Person A: Wait….you actually believe the earth was created 6000 years ago so that means you are a young earth creationist correct? How is that an ad hominem?

Person B: I just believe what’s true.

Person A: Umm, no you don’t. You just believe what you want to believe is true, not what’s demonstrably true.

Our hypothetical discussion is going nowhere fast and while intended to illustrate Person B’s false claims of ad hominem arguments, also shows us a glimpse of someone who isn’t really interested in the evidence. They have accepted a conclusion in the absence of any evidence to support that conclusion.

Stick to what’s true and try, as frustrated as you might feel, to refrain from using ad hominem attacks. Just as importantly, practice recognizing them so that you can, dare I say, inoculate yourself against them when they raise their big fat stupid heads.