For example, assume these two propositions.
A.) My mother is real
B.) The earth is a sphere
How does one show, as a matter of fact that believing in A.) is more reasonable than B.)?
One may point to B.) as most would do intuitively and claim that A.) is possibly false and B.) doesn’t seem to be. But B.) can be conceived of as being false. It is possible that you’ve simply been lied to, and people have all coalesced together into fooling you that the earth is spherical when it is instead flat.
Of course, the response would be that the probability of that is very low. But what does this mean and how does one justify this? We don’t have a series of possible worlds in which to check how often people try to fool others into thinking that the earth is a sphere.
So again, as a matter of fact, how does one show that believing in B.) is more reasonable than A.)? Note that I am not asking about how one can come up with a system or model to represent comparative reasonableness. Nor am I asking about whether humans seem to feel, as a matter of psychological fact, more confidence in one belief over the other.
My question is moreso in what ontological sense do these degrees of reasonableness actually exist? Is there an objective level of reasonableness of belief A more than belief B? If not, as Russell would put it, is there no intellectual difference between people that we would consider sane vs insane?