Logical Fallacy Friday: Argument from Ignorance or Burden of Proof

The Colbert Report had a fantastic example of argumentam ad ignorantium last night, in which Colbert confronts the head of Consumer Reports claiming that because the interviewee cannot prove that certain things are harmful in a way that the interviewer will accept, the interviewee is therefore wrong:

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This is also known as the “Burden of Proof” fallacy.  The effect is to insist that Person A’s premise is wrong if Person A cannot prove that premise beyond a shadow of a doubt.  Sometimes this demand is entirely appropriate.  Our justice system places the burden of proof on the prosecution in order to prevent innocent people from being punished (I’m not saying it’s always effective).  Similarly, in an argument, the burden of proof is usually placed on someone making a new, radical, or improbable claim in the face of established principles, but the argument from ignorance becomes a pernicious debating tactic when Person A essentially declares victory on the issue because Person B has not proven their premise in terms that Person A will accept.  Let’s look at some examples:

“It’s just a theory.”

When I went to Evangelical High, I often heard this one get thrown about with reference to evolution.  “Evolution is just a theory,” they would say, the implied conclusion being that without further evidence, we should just go ahead and accept that the entire universe was created in six twenty-four hour days by an omnipotent being  as it is described in the Book of Genesis.  Of course, the problem with this logic is that scientific theories are usually based on something, like empirical evidence or inductive logic.  Furthermore, as my biology-teacher partner frequently says, when people talk about the theoretical nature of evolution, they are usually talking about macro-evolution, the process that took us from amoebas to primates, a phenomena that we cannot directly observe because it takes gazillions of years to occur.  Micro-evolution, or mutation, is something we observe all the time.  If you believe in cancer, you believe that some form of evolution occurs.

“We need to conduct more tests.”

This one is a perennial favorite of the tobacco lobby, which has historically insisted that until we do random-assignment, double-blind, longitudinal studies of smoking, we cannot know for sure that it causes cancer and emphysema.  The thing is, randomly assigning some people to engage in a behavior we’re pretty sure will kill them, especially over a long period of time,  presents something of an ethical conundrum.  This is equivalent to Colbert’s insistence in the video clip that we conduct studies on whether or not electrocution makes people immune to electricity before we place warnings on electrical devices.

My father, a physician who works on the cutting edge of a particular surgical field, encounters a similar problem related to the insistence on “evidence-based medicine.”  Often, the sorts of protocols that one would use to prove that a pharmaceutical product is effective are not applicable to experimental surgery due to ethical or pragmatic concerns.  Surgeons frequently have to support their techniques with evidence based on physiology and case studies rather than RCTs (randomized controlled trials), the gold standard of evidence-based medicine.

“You need to present evidence from sources I will accept.

Returning to Evangelical High for a moment, I had a Bible teacher who used to say, repeatedly, that if we wished to argue with him about any premise, we had to use evidence from the Bible.  Now, just about any theologian (or person with an ounce of common sense) will tell you that the Bible is not a Magic Eight Ball.  The Bible is silent and/or extremely vague on any number of issues, including immigration reform, universal health care, String Theory and what I should have for breakfast in the morning.  In fact, I believe the Bible has nothing to say on the subject of whether or not the US government created the AIDS virus, a theory that he espoused on our very first day of class.  (But I’m pretty sure this guy thought God was personally giving him answers on those issues as well.)  Furthermore, what it does say has been the subject of two millenia of exegetical arguments, so what he was really saying is “you must be able to cite the Bible in a way that is consistent with my interpretation of it.”  Essentially, this was code for “you can never, ever argue with me and must accept–as God-breathed truth–every utterance that passes my lips.”

But probably everyone’s favorite variant of this fallacy is the Birthers, who, when presented with Barack Obama’s Hawaiian birth certificate, declared with a straight face that this particular birth certificate did not convince them.  As in the previous example, the rhetorical effect of this move is to insist that you will only be convinced if presented with evidence that does not or cannot exist.

“I can’t imagine how that could be true.” (Trigger warning)

A favorite of The Defendant’s Mom, this one asserts that incredulity carries more weight than actual evidence.  We hear this one a lot when a Nice Middle Class White Boy physically assaults or rapes some girl, or when a valued family member is exposed as a serial molester.  This is not to say that evidence based on personal experience with a person is invalid.  It is only fallacious when one uses beliefs about a person’s goodness to counter other forms of evidence. For example, in the clip, Colbert asserts that his “consumer testing” is based on faith rather than science.

“It hasn’t been disproven.”

This fallacy insists that because a premise has not been disproved beyond a shadow of a doubt, it may or must still be true.  An extreme example would be someone who insists that because no one can prove that he was not abducted by aliens, his claim that he was abducted by aliens must be accurate.  But the “no one has disproved this” fallacy is quite common in the way people talk about null studies that relate to commonly held beliefs about scientific topics like nutrition.  Sandy Swarzc of the blog Junkfood Science sums up the importance of null studies thus:

Beliefs and ideologies can be stronger than the science, especially when it comes to our diets. Sadly, so can our fears. Millions of Americans take vitamins and worry about what they eat, fearing that if they fail to eat loads of antioxidants, free radicals will lead to heart disease, cancers and other chronic diseases of aging. Yet, the strongest studies continue to show these concerns to be unsupported.

Remember, science can never prove something beyond all doubt, but it can disprove an hypothesis or scary claim. That’s why sound clinical trials, designed to be fair tests of hypotheses, that fail to support a belief, and show us there is nothing to worry about, are the most important of all. But for those null studies to help us, we first have to hear about them.

Swarzc uses the example of a null study that showed no relationship between taking vitamin supplements and a reduced risk of cancer or hypertension, and perhaps more importantly, no relationship between not taking vitamin supplements and an increased risk of cancer or hypertension.  Null studies do not technically prove anything, but by subjecting a premise to the most rigorous tests demanded by science and failing to find that premise true, they show the chances of that premise being true to be incredibly slim, slim enough to consider the premise debunked.

Previous LFF posts:  straw man, ad hominem, reductio ad hitlerum


5 thoughts on “Logical Fallacy Friday: Argument from Ignorance or Burden of Proof

  1. This is on of my favorite logical fallacies, second only to the appeal to nature fallacy. And by favorite, I mean most rage-worthy.

  2. This is a great post, with great examples. Thanks for writing it.

    “You need to present evidence I will accept.” This is the most maddening one for me. Very, very few of those who use this can be convinced of their errors if you reason on their level. Yet, people continue to attempt it all the time, especially online. Once I see a discussion headed in this direction, I bow out. They may think that they have won, but some are beyond reasoning with.

    1. Is this also like, “You need to use websites with my bias because you’re just giving me all kinds of liberal websites with this information.” Yeah, ’cause the FRC is going to have the true stats on gay adoption.

  3. I love this post! I’ve often thought something along these lines but never properly formed the thought in my own mind. Especially, the evolution arguement. How can people possibly compare Genesis and evolution?! No it can’t be fully proven, but at least it has some kind of reasoning behind it and some scientific example. Nothing of the sort for the bible! It makes me want to wrap every bible up in Tamper Evident Tape so that no poor unknowing children get taught that the stuff in it is truth rather than moral guidance!

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