As I understand it, the notion that religious truth-claims (such as "the gods exist", etc) need to be justified by some rational means dates all the way back in Western thought to Thales of Miletus, who lived around 600 BCE in what is now Asia Minor.
As with most things, the details are sometimes disputed, but it seems most scholars agree that Thales began the Western tradition of assuming that all natural events have causes which can be discovered by reason.
An alternative view would be that the causes of natural events are known only to authorities -- such as priests -- or revealed only by traditions. That was the view that seems to have prevailed before Thales. It should be easy to see how the notion that natural events have causes that can be discovered by reason can morph over time into a demand that even religious truth-claims make rational sense. Indeed, the rise of theology in the West is almost certainly a consequence of Thales' revolutionary idea that the nature of things can be discovered by reason for theology is basically an attempt to figure out rational reasons for religious truth-claims (whether it succeeds in doing that is up to you to decide).
Do you think it's a good idea to demand a rational basis for religious truth-claims? Why or why not?
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