created by AnEpiphanyTooLate on 07/08/2016 at 00:10 UTC
6 upvotes, 3 top-level comments (showing 3)
It's Carl Sagan's famous maxim and I've seen it spread like wildfire among Internet New Atheists, which is exactly why I'm skeptical of its veracity. What do philosophers in general think of this statement?
One objection I can think of and have heard somewhat by theists is that it fails to define what an extraordinary claim is, so anyone can just claim something is an extraordinary claim and then dismiss it because it doesn't have extraordinary evidence backing it up. This seems plausibly damning to this statement but I'm curious about someone properly fleshing this out or responding to it.
Comment by wokeupabug at 07/08/2016 at 00:29 UTC
10 upvotes, 1 direct replies
I'm not sure that the expression involves anything more than a colourful way of indicating the general maxim that if we advance a claim we expect others to agree to, we ought also to provide some support adequate to rationally motivating this agreement.
Comment by willbell at 07/08/2016 at 04:05 UTC
3 upvotes, 0 direct replies
I think one could conceivably - and I mean conceivably in the sense that would be beyond any measure of reasonable degree of charity to Sagan or atheists who advance that line - make it out to be about the morality of belief.
Take for instance the claim that I had eggs for lunch today, that's a claim with very low impact on your worldview, in fact it won't change much of anything about how you act ever again. Therefore, you could take it on my word and probably not have a problem with it.
A claim like "all morality is subjective" or "there are ghosts walking the Earth and I can put you in touch with your dead dad if you pay me well enough" has higher stakes on a moral scale. If I believe all morality is subjective, maybe I'll start acting like a worse person, lying, cheating, stealing, etc, then if I'm wrong I've done something terrible! If I start following a cultist around and commit to a suicide pact, or I get defrauded out of my money by a psychic then my beliefs were highly consequential. Thus for moral reasons I am required to take a higher standard before taking on a belief.
Just to reiterate, I doubt Sagan thought of any of these facts, and so this has no impact on the quality of the statement as expressed by him or others who take after him.
Comment by under_the_net at 07/08/2016 at 09:22 UTC*
2 upvotes, 3 direct replies
The claim (which is attributed to Marcello Truzzi[1], but can also be found in Laplace and Hume) can be made precise using Bayesian epistemology.
1: https://en.wikipedia.org/wiki/Marcello_Truzzi
Let *C* be your claim. *C*'s being extraordinary can be explicated by the idea that *C*'s prior probability *p(C)* is very low.
Let *E* be your evidence for *C*. *E*'s being evidence for *C* can be explicated by the idea that the probability *p(E|C)* of *E* given *C* is high; let's just say *p(E|C)* > 0.5.
Using Bayes' Theorem,
If we want *E* to to make *C* more likely than not, we need *p(C|E) > 0.5*. Given the above, this requires that *p(E)* =< *p(C)*, which, since *p(C)* is already low, means that *p(E)* must be *at least* as low. In other words, *E* needs to an extraordinary claim too.