As for 'reasonableness', it is isn't necessarily a good criterion for whether a belief is true, but it can be an indication of how amenable someone is to empirical evidence. For example, to a 14th century peasant, a belief in god was more 'reasonable' than it is now because she wouldn't have had access to information about alternative explanations for the origin of life and of biodiversity. It is much less reasonable to hold the same belief today, after being exposed to the theory of evolution and the mountain ranges of evidence which keep clawing away at the claims made by religion. The point of calling a belief unreasonable is to point out how far someone is bending over backwards to hold onto that belief, despite all the evidence to the contrary.
The upshot of this is that religions, conceived of as (deductive or inductive) moral systems, may indeed have self-contradictions. But the existence of self-contradictions does not necessarily invalidate their truth value or usefulness. Moral systems are different, of course, from scientific models, because they are prescriptive and normative rather than descriptive and positive. Thus their bases for 'truth/falsity' are profoundly different. Whether this difference affects the significance of self-contradiction is unclear.
I don't claim to understand the Standard Model, or the oft-cited particle- and wave-like nature of light as it is understood today; but when a generalization in science encounters an exception, the generalization is scrapped or amended to fit the data. Previously the assumption was that Newtonian physics applied universally -- well that was not true, Newton's laws fail where special relativity and quantum physics become necessary to explain phenomena (right?). It doesn't mean that apples no longer fall from trees, but it does mean that the premise, 'Newtonian physics applies universally' is false. That's fine, the statement can be amended and most observations we based on the initial assumption will still be accurate under normal conditions. Oranges and lemons will still fall from trees.
These are not the kind of contradictions religion faces (like the problem of pain and suffering under a benevolent, omniscient, omnipotent god), which are fundamentally devastating because they disqualify a belief in god, the obedience to which is the foundation of Judeo-Christian moralities. More than the Standard Model, religion in this sense is more like alchemy.
The moderately religious will amend their belief system to shed the more obvious falsehoods, but once a person does this, she can't honestly cite faith over reason as the foundation of her beliefs -- her beliefs become vulnerable to empirical arguments.
I don't think I'm clear on what you mean by 'truth value' then. If we accept that the empirical evidence suggests that the existence of god is either impossible or only minutely probable depending on how god is defined, what truth value is left in Christianity?
Religion definitely is useful in establishing moral systems. But the moralities it has created so far have serious and obvious flaws -- flaws which are the logical extension of the original premises of the religion. I'd even go as far as to say that in general, they do more harm than good, keeping in mind that even those who profess to be religious do good for reasons independent of their belief in god. This must be true especially of Christians who don't believe in hell.
What are some other things by which religion would still have truth value, even if its premises were false? Liar was necessarily vague about this, and I just don't see how religion as a model of the universe can be useful to a society with secular alternatives in theories of morality, ethics, and every other field of thought and endeavor over which religion previously had a monopoly.
Reason itself commits a kind of epistemological Original Sin in that it can't be used to justify its own supremacy over reason, but it is what we use, usually successfully, to determine the nature of reality; and when we fail, typically we have missed data. I don't see why the methodology should change, to the arbitrariness of faith based on tradition, when we address the Most Important Questions; and how it isn't hypocritical for the religious to claim they value faith over reason but then proceed to live their lives using the rules of logic.
When you say that "if society can act successfully over the long term on the basis of a conceptual model, then that model is at the very least 'justified' if not 'true.'", I don't really disagree. I just cannot see how religion is that successful model, or at least how it could be more successful than a moral system which equates good with life and productivity, evil with pain and suffering; without any need for cog diss, dogma, divinely mandated exceptions for jihad and other theological loopholes which the powerful can exploit and have exploited thousands of times before to establish theocracies or to justify atrocity.
I'm not asking you to defend religion, but I guess I just want to say that accepting the pragmatist model of 'truth', religion is still a poor model to hold onto.
But you are still accepting the same criterion of truth: usefulness in prediction and action. Liar may just find the perspective more useful than you do.
I'm not sure that I do. My criterion was correspondence to reality, and the hypothesis - confirmation cycle was merely evidence. I think our model of the solar system is both true and useful, but I don't accept that they are the same thing. (I'm not well read in positivism, but conflating usefulness and truth still seems like a rhetorical trick to me.)
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