Logical Fallacy Lesson 10: Argumentum ad Ignorantiam

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Logical Fallacy Lesson 10: Argumentum ad Ignorantiam
Category: Religion and Philosophy


Samuel Thomas Poling, Blog 138, Logical Fallacy Lesson 10, Argumentum Ad Ignorantiam

LFL1: Argumentum Ad Hominem
LFL2: Red Herring
LFL3: Non Sequitor
LFL4: Bald Assertion
LFL5: Ad Hoc
LFL6: Argumentum Ad Nauseum
LFL7: Appeal to Faith
LFL8: Appeal to Emotion
LFL9: Shifting the Burden of Proof
And Now LFL10: Argumentum Ad Ignorantiam

My original source of logical fallacy knowledge, Glen Whitman's "Logical Fallacies and the Art of Debate" essay, misspelled Ignorantiam as Ignorantium - so I consequently misspelled it as well in my last blog. Sorry. It's with an "a" not a "u." Well, according to most internet sources. I got 922 google hits for "Ignorantium" and 128,000 for "Ignorantiam," so I'm going to go ahead and bet on "Ignorantiam" as the correct spelling - although it really doesn't matter.

Anyways, it is important you read my last blog before reading this one, for this fallacy is almost identical to the "Shirting the Burden of Proof" fallacy. As a matter of fact - most of the time they are identical. Shifting the Burden of Proof is the most common form of Argumentum ad Ignorantiam and I go into detail about it in my previous blog. For that reason I am personally considering this blog a continuation of my previous one, Logical Fallacy Lesson 9.

So I shall skip the Shifting the Burden of Proof form of this fallacy and move on to the other forms of this fallacy.

Argumentum ad Ignorantiam is any appeal to ignorance. Appealing to ignorance is not fallacious in and of itself. Like all logical fallacies, the just committing the "title" of the fallacy isn't fallacious. It's how, when, why, and for what purpose you intend to us the appeal which determines whether or not it is fallacious.

If you are in the negative, for example, and you say "you haven't proven the side of the debate yet, we still don't know whether or not there is a God," you are technically appealing to ignorance, but you are not guilty of anything illogical.

If you say, "We don't know if there is a God, therefore we know there isn't one," or if you say, "therefore we know there is one" you are being illogical and making the fallacy argumentum ad Ignorantiam. The second example, of which, is the Shifting the Burden of Proof fallacy. Just because something isn't proven false doesn't mean it is proven ture. Like in court, someone is innocent until proven guilty.

Although, to be fair, something isn't disproven just because it isn't proven.

No one can aver something as disproven unless they can prove that as well. Appealing the ignorance their is just as illogical as appealing to it to prove something.

If you don't know, ladies and gentlemen, then guess what?

It isn't proven.
It isn't disproven.

You don't know.


It is fallacious to say you do know one way or the other just using "we don't know" as your excuse. As a matter of fact, it's contradictory. We don't know means we don't know, not "therefore my side is proven." It's like saying one plus one equals two, therefore it equals three, or "the chip in that had could be either red or blue, we don't know, therefore it's blue."

It's insanity. If you don't know the color of the chip, then it isn't yet proven to be red or blue. Appealing to your ignorance, your lack of knowledge on what color the chip is, doesn't mean it's proven to be either color.

Finally, a type of Argumentum ad Ignorantiam is an argumentum from personal incredulity. Appealing to your personal ignorance on the subject by the means of saying, "you just don't understand" or you "fail to grasp" it. Just because you don't understand something doesn't mean it isn't true.

"I just don't see how a cell can become a human over 4.5 billion years..."
"Well, good for you."

Anyways, here is what infidels.org has to say about Ignorantiam in their logical fallacy section:

Argumentum ad Ignorantiam
Argumentum ad Ignorantiam means "argument from ignorance." The fallacy occurs when it's argued that something must be true, simply because it hasn't been proved false. Or, equivalently, when it is argued that something must be false because it hasn't been proved true.

(Note that this isn't the same as assuming something is false until it has been proved true. In law, for example, you're generally assumed innocent until proven guilty.)

Here are a couple of examples:

"Of course the Bible is true. Nobody can prove otherwise."

"Of course telepathy and other psychic phenomena do not exist. Nobody has shown any proof that they are real."

In scientific investigation, if it is known that an event would produce certain evidence of its having occurred, the absence of such evidence can validly be used to infer that the event didn't occur. It does not prove it with certainty, however.

For example:

"A flood as described in the Bible would require an enormous volume of water to be present on the earth. The earth doesn't have a tenth as much water, even if we count that which is frozen into ice at the poles. Therefore no such flood occurred."

It is, of course, possible that some unknown process occurred to remove the water. Good science would then demand a plausible testable theory to explain how it vanished.

Of course, the history of science is full of logically valid bad predictions. In 1893, the Royal Academy of Science were convinced by Sir Robert Ball that communication with the planet Mars was a physical impossibility, because it would require a flag as large as Ireland, which it would be impossible to wave. [Fortean Times Number 82.]

See also Shifting the Burden of Proof.

Alright, that's it for this blog. I might do the next one specifically on the argumentum from personal incredulity.

Samuel Thomas Poling, Blog 138, Logical Fallacy Lesson 10, Argumentum ad Ignorantiam