Date: May 18, 2011 06:00PM
Thanks to RPackman for artfully pointing out the fallacy of the couplet, "Absence of evidence is not evidence of absence."
If one takes the Bayesian view of evidence, “evidence” would be any state of affairs the existence of which makes a given theory or claim more probable than it would be in the absence of such state of affairs. Upon this definition, the absence of a college record of Jack’s Phd is a state of affairs that makes the theory that Jack does not have such degree more probable than it would be in the absence of such a state of affairs. (And correspondingly, the alternative claim that he has such a degree more improbable) However, Jack’s assertion of his Phd status is itself evidence of such by the same principle, simple because such a statement makes the theory that he has such a degree more probable than it would otherwise be. The issue, then, is weighing the evidence, and assessing, intuitively or otherwise, the probabilities of a given theory or claim being true, given the evidence.
Note, however, we should be leery of any cute couplets used as rhetorical devices in either science or religion. Often they turn out to be false or nonsensical.
For example, the quote, “That which can be asserted without evidence, can be dismissed without evidence,” attributed to Christopher Hitchens, is also false. The fact of the matter is that a great deal of scientific theory is first asserted either without evidence, or with very weak evidence, offered merely as a possible explanation for a given phenomena, only later to be confirmed or disconfirmed, by evidence and discussion. Some scientific theories thrive for decades without any evidence beyond mathematical consistency. Much of modern theoretical physics and cosmology exists as mere mathematical theories without direct supportive evidence. Often such unsupported theories have great explanatory power, which make them attractive and worthy of pursuit, the lack of evidence notwithstanding. Einstein’s theory of special relativity is a case in point. When offered it had nothing more than great explanatory power. Later it was confirmed by direct evidence.
The couplet, “Extraordinary claims require extraordinary evidence," attributed to Carl Sagan, is also problematic. Again, extraordinary claims are often made in science without evidence, or minimal evidence. They do not require extraordinary confirming evidence, just ordinary evidence. Their viability is based upon their explanatory power, and their susceptibility to confirmation or falsification. There was nothing wrong with the extraordinary theory that the ancient Americans were descendants of the lost 10 tribes. As a theory, it had explanatory power, and was falsifiable, and in fact has been falsified. The implication of the above couplet is that extraordinary claims require extraordinary evidence, in order to warrant belief. But this is also false. Belief is sometimes warranted in the absence of any evidence, if the theory believed offers the best explanation for a phenomena in question, or if, as a practical matter, belief is more efficacious than disbelief. There was a time when the idea of God offered the best explanation for the complexities found in nature, particularly the existence of life. No extraordinary evidence was required to support this claim, it just seemed like the best explanation. Later, it was supplanted by evolution as the best explanation, much to the chagrin of theists.
Finally, it can be noted that it is false to claim that there is no evidence for ancient civilizations consistent with the descriptions in the Book of Mormon. The Book of Mormon itself is evidence for such claims, notwithstanding the fact that it is weak, and fails to be confirmed by modern archeology, anthropology, and genetics. As indicated above, like most controversial issues, whether in science or religion, the question is whether the proposed theory provides the best explanation for the phenomena in question. If the phenomenon in question is the existence of ancient American civilizations, the Mormon explanation is simply no longer viable. But this does not assume that it was always ludicrous, or that it required extraordinary evidence. Regular evidence could have confirmed it, the same type of evidence that falsified it.