Wednesday, January 5, 2011

Historical Fallacy of Negative Proof

Paul Newall writes:
The fallacy of negative proof occurs when the lack of evidence for something is taken to justify the conclusion that it did not exist. The logical error involved becomes obvious when shown as a syllogism:

P1: No evidence has so far been found for A;
C: Therefore A did not exist/happen.

This is a formal fallacy: what is needed is an additional premise, to the effect that no evidence for A will ever be found subsequently.

A good example of this fallacy is found in studies of historical figures or events, especially religious ones, such as the debate over the historicity of Jesus or the existence of Atlantis. Where a person is referred to in stories or sagas, say, but no other evidence of their actual existence is found, should we conclude that the person is fictional? Notice that there is a considerable difference between claiming that the lack of evidence proves that the person did not exist (i.e., the negative proof fallacy) and asserting that the likelihood of their historicity is small; however, an elaboration of how such probabilities are assigned is still required.

Paul Newall, "The Logical Fallacies of the Historian" in A Companion to the Philosophy of History and Historiography (Blackwell Companions to Philosophy), pp.270-1.


  1. I would agree that we can not say the person is fictional. But at the same time we can not affirm that the person is real.

    In order to place someone historically we need independent sources to provide reliable facts, and hopefully physical evidence. I can assure you my great-great-grandfather existed even though I do not know his name or how he looked liked as I am physical evidence. But can we prove/disprove that he had a brother? We would need some evidence to prove or disprove that.

    Anyway, interesting blog, hopefully I'll get to read more of it.


  2. Hey! The existence of a great-great-granduncle would be dealt with in probabilities based on the evidence we have available. Did you just make it up? The probability is quite low. Did you know from a reliable witness or chain of witnesses? Substantially higher, etc. Without physical evidence (we could do DNA tests world wide:p) we can still establish a high probability. Conversely, if you did not know that you had a great-great-granduncle it would not mean there never was a great-great-granduncle. Without good reason (hypothetical parent died after birth of earlier sibling) or sources (a diary lamenting only one child, a will document), it would be difficult to definitively conclude that it is probable that someone did not exist, especially if the reason we are investigating is because for some reason or another they exist in someone's mind.

    I don't think I want to re-read what I just said in case I just committed a logical heresy. Thanks for the comment!