Quote:
Originally Posted by John21
I’m doing so because my point is about logical necessity and logical impossibility. If something is logically impossible, it’s physically impossible. So there’s no point in looking for empirical evidence for something like a plane figure that is both round and square to raise or lower the probability it exists.
Your mistake here is that you are conflating an a priori claim with a metaphysically necessary claim. These are conceptually separate ideas - one refers to an
epistemic characteristic while the other is a claim about the nature of reality. For instance, an identity claim like:
Mark Twain (if he exists) is Samuel Clemens.
is plausibly a metaphysically necessary claim (true in all possible worlds) since it is an identity statement with two proper names, but this is not an a priori truth of the world, but rather something we discover empirically.
The claim that p is evidence for a necessarily true (if true) claim d should be understood as an epistemic claim, as updating our Bayesian prior of the probability that a necessarily true (if true) claim d is actually true. For instance, if someone announces a new math proof, we often initially do not believe it is true until it has been checked by experts, while still acknowledging that if true it is necessarily true. A second announcement that it is sound after being checked by independent experts would still function as evidence for it being true.
Last edited by Original Position; 11-04-2018 at 03:52 PM.
Reason: clarity