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Fallacy Friday: Ad Ignorantiam (Arguments from Ignorance)

April 8th, 2011 by Matt

In the discussion following last week’s Fallacy Friday topic, Ad Populum, LJ asked about the ad ignorantiam fallacy. In particular she wanted to know about its relationship to creationism. I suspect LJ was being sarcastic but despite this it is worth exploring this issue a bit.

First, we should recall that a fallacy is not simply a false position on some subject. The fact that someone expounds a mistaken view in theology, philosophy, science, law, ethics or any other subject does not necessarily mean that that person has committed a fallacy. A fallacy is a common mistake in reasoning. A fallacy occurs when one attempts to infer a conclusion from a premise in an invalid manner. I noted in Assessing Arguments that an argument can be valid even if it has false premises and false conclusions. So the fact that someone believes in or propounds contemporary evolutionary theory or creationism or something else does not, in and of itself, mean that that person has committed the ad ignorantiam fallacy.

What is an Ad Ignorantiam?
"Absence of evidence is not evidence of absence" Carl SaganSo what exactly is the mistake being made when one commits an ad ignorantiam fallacy and how does one commit it? The ad ignorantiam fallacy is as an argument from ignorance. It occurs when a person argues that a conclusion is false because no one has shown it to be true or when a person argues a position is true because no one has shown it to be false.  Applied to evolution, the argument has the form:

1. No one has shown that evolutionary theory is true;

Therefore:

2. Evolutionary theory is false.

Similarly, with creationism:

1. No one has ever shown creationism is true

Therefore:

2. Creationism is false.

What the person who makes this inference fails to appreciate is that the failure to provide a reason for affirming a conclusion is not the same as providing a reason for thinking the conclusion is false. It is possible, and probably actual, that there are many things that are true which we do not yet know about. In such situations, no one will have shown these things to be true and no one will be able show them to be false yet they are true; we simply will not know that they are.

An example from history might illustrate this; consider the heliocentric hypothesis, the claim that the sun is the centre of the solar system and the planets, including the earth, orbit the sun. There was a time centuries ago when no one had shown this was true; was it false? Obviously not. It was true but people simply did not know it was. All that the absence of reasons for thinking something entails is that we have no reasons for affirming that thing.

What  is Not an Ad Ignorantiam
There is an interesting line of argument that is sometimes used in debates which is not an ad ignorantium. This is the argument that a particular position cannot be rationally accepted because no one has shown it to be true.  Suppose someone argues that:

  1. If we have no compelling proof for a position then it is irrational to accept that position as true;
  2. We have no compelling proof for  X;

Therefore

3. It is irrational to accept X as true.

This argument is not an ad ignorantium; it is clearly valid. It is such that if the premises 1 and 2 are true then the conclusion 3 cannot be false. Of course this does not mean that the argument is sound. It could be that the premises are false. I  think there are some serious problems with the claim asserted in 1. for example, and wether 2 is true will depend on what one replaces the variable X with. But the point is, regardless of the truth or falsity of the premises, the argument is valid. It does not infer that a position is false from the premise that no one has shown it to be true. It infers that the position is irrational from two premises; the first is that the position has not been proven but there is also a second premise: that beliefs need to be compellingly proven to be rational.

Application: The Creationism/Evolution Debate
Suppose we then apply this to the creationist/evolution debate. Creationism itself does not commit the  ad ignorantium fallacy. Creationism is, after all, a conclusion. Likewise, Evolution does not commit the fallacy either as Evolution is a conclusion. Particular protaganists of these positions commit this fallacy only if they offer certain types of arguments for their positions.

If a creationist argues that creationism is true solely on the basis that evolution has not been proven then he commits the fallacy. Most creationists that I am aware of, however, do not argue this way. They believe there are good reasons from scripture and good empirical research for thinking that the world was created in 6 x 24 hour days. Their belief that evolution has not been proven exists alongside this belief. Similarly, most evolutionists I know believe there are good reasons from empirical research for believing evolutionary theory is true. They do not, as far as I can tell, commit the fallacy either.

Of course, the fact that they do not commit one particular fallacy tells us little; it could be that the arguments they offer commit other fallacies or it could be that the arguments are valid but have false premises. It is not given that when someone says something that is false that they have committed a particular fallacy. Sometimes the problems with a mistaken position lie elsewhere. It is simply not the case that when someone puts forward a view that I think is mistaken that he has to be committing a fallacy. Part of learning and gaining understanding is gaining an accurate understanding what one’s opponent’s reasons are for disagreeing and then working out where exactly, if anywhere, the mistake actually lies.

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4 responses so far ↓

  • Thanks Matt, all too often I think that someone just saw a fallacy described somewhere, and then decided that whoever holds a position they disagree with must be committing said fallacy.

    The philosophical equivalent of “to a man with only a hammer, every problem looks like a nail.”

    It is perfectly possible for every side in an argument to have completely valid arguments, yet for one (or both) to be completely wrong.

  • This is good stuff. Are we raised to argue from a position of ignorance? The creationism/evolution debate is a great example.

    “Part of learning and gaining understanding is gaining an accurate understanding what one’s opponent’s reasons are for disagreeing and then working out where exactly, if anywhere, the mistake actually lies.”

    This is dead on. If we realize that we don’t know everything we can learn a lot more from each other. I always say that the more I know, the more I realize I don’t know.

  • There are more forms of creationism than the “literal 6-day” creationism. Old Earth Creationism is a valid view of creationism, a la http://reasons.org/

  • Matt, I was listening to these over the weekend while I was piling firewood and really enjoyed them. However, what “good empirical research” is there to support the suggestion “that the world was created in 6 x 24 hour days”? TAM.