A Bayesian approach to the argument from ignorance

Can J Exp Psychol. 2004 Jun;58(2):75-85. doi: 10.1037/h0085798.


In this paper, we re-examine a classic informal reasoning fallacy, the so-called argumentam ad ignorantiam. We argue that the structure of some versions of this argument parallels examples of inductive reasoning that are widely viewed as unproblematic. Viewed probabilistically, these versions of the argument from ignorance constitute a legitimate form of reasoning; the textbook examples are inductive arguments that are not unsound but simply weak, due to the nature of the premises and conclusions involved. In an experiment, we demonstrated some of the variables affecting the strength of the argument, and conclude with some general considerations towards an empirical theory of argument strength.

Publication types

  • Clinical Trial

MeSH terms

  • Bayes Theorem*
  • Humans
  • Logic*
  • Models, Psychological
  • Persuasive Communication*
  • Thinking*