Sunday, January 22, 2012

ad populum fallacy

The ad populum fallacy is the appeal to the popularity of a claim as a reason for accepting the claim. The number of people who believe a claim is irrelevant to the truth of the claim. Fifty million people might believe the Sun revolves around the Earth, but how many people believe or don’t believe something is not relevant to whether what they believe is true. The ad populum fallacy is also referred to as the bandwagon fallacy, the appeal to the mob, the democratic fallacy, and the appeal to popularity.

It is not always irrelevant to identify how many people make a claim. When the majority of experts in a technical field such as climate change agree on something that the average citizen does not understand, it is not a fallacy to accept the consensus viewpoint. Of course, the majority of scientists could be wrong about an issue, but it is not irrelevant to cite the consensus viewpoint of experts in a technical field as a good reason for accepting a claim. Presumably, the scientists agree because of the overwhelming evidence for their position. This is quite different from the case where non-experts agree on something traditional, such as the existence of devils or ghosts. Claiming that ghosts or devils must exist because millions of people believe they exist would be an ad populum fallacy.

Advertisers are fond of this fallacy. So are defenders of alternative health practices or CAM, complementary and alternative medicine. Apparently the National Center for Complementary and Alternative Medicine (NCCAM) thinks that CAM becomes more respectable if large percentages of people use one or more of its modalities. NCCAM claims that 38% of American adults used some form of CAM in 2007. The problem is that some of the modalities it considers as CAM are a bit odd. The NCCAM lists dieters, exercisers, and people who practice Yoga as using CAM. At one time, NCCAM included prayer as a CAM modality. The fact is that CAM is not that popular: most American adults don’t use acupuncture, energy healing therapy, reiki, naturopathy, Qi gong, Tai chi, or homeopathy. NCCAM exaggerates the popularity of CAM to validate not only the various modalities it lists, but to validate its own existence. The fact that nothing worthwhile has issued from NCCAM despite the 2.5 billion tax dollars it has spent in its more than two decades of existence might make a citizen question the continued funding of the agency. The fact is that CAM modalities do not become validated by how many people use them, but by whether they have been shown to have a positive effect on health that is superior to doing nothing or to placebo effects. 

Politicians are also fond of the ad populum fallacy. They love to point out that their views are popular or to point out that their opponents are out of step with public opinion. The fact is that public opinion is often out of step with reality.


  1. Hi,

    I'm really enjoying this series, thanks so much!

    Just FYI, though, I use google's RSS reader, and it renders your text with many of the spaces deleted. Don't know why.

    Again, thanks for the info.

  2. Thanks. I don't know why Google's RSS reader would delete spaces, though.

  3. You write that public opinion is often out of step with reality. Moreover, this is regarded as a FACT.

    This is close to an intellectual's wording for the opinion that common folks are stupid. Please rephrase if it's not what you intended to communicate.

    1. It actually means the public at large is ignorant. That's an important distinction as well as a demonstrable claim.

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