No. 274 · Evidence · Fallacy
Appeal to Ignorance
No evidence of harm is not evidence of no harm, unless someone has really looked.
In the Almanac
“Thalidomide”, 1957–1961 · “Purdue Pharma”, 1996–2020
Both stories in full, three ways to use it and where it misleads.
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Questions
What is Appeal to Ignorance?
The appeal to ignorance treats a lack of evidence as if it were evidence. "No proof of harm" can sound reassuring, yet it often means nobody has looked properly.
How do you avoid Appeal to Ignorance?
When someone settles a question with "there's no evidence", ask how hard anyone searched, and whether that search would have found the answer if it existed. A careful search that finds nothing means something. Silence alone does not.
When does Appeal to Ignorance matter?
Appeal to Ignorance is one of the 68 mental models for evidence, the situations where you ask: Is this really true? Within that, it belongs to “Spotting a bad argument”, alongside Ad Hominem, Appeal to Authority and Appeal to Emotion.
What is an example of Appeal to Ignorance?
Two stories show it at work: Thalidomide (1957–1961) and Purdue Pharma (1996–2020). Both are told in full in The Mental Models Daily Almanac, which has two stories for each of its 365 models.
Which mental models are related to Appeal to Ignorance?
Unknown Unknowns, False Negative and Falsification. Appeal to Ignorance itself comes from fallacy.