The Presumption of Naturalism: Is it Rational?

[Haven]

Over on the "alleged resurrection of Jesus" thread, I posted this:

This post won't be popular here among my fellow atheists, but I think the Christians have a very valid point on one matter -- the circularity of atheists'/skeptics' arguments against the resurrection.

Almost every atheist I've talked to on [the subject of the resurrection of Jesus] (at least the ones who do not accept the Christ myth theory) uses circular logic to argue against the resurrection. We assume a priori that naturalism is true, and from there we reason that the resurrection did not occur, even when the evidence seems to go against our claim. This, of course, is fallacious, committing the logical fallacy of begging the question, but atheists -- nearly without exception -- use this method of argumentation against the resurrection. We won't even consider the evidence in favor of the resurrection, which, when approached from a truly unbiased perspective, is at least somewhat substantial, we simply handwavingly dismiss the possibility that a "magic zombie Jesus" is possible . . .

Debate question: Should one presume naturalism is true when evaluating a given proposition? Is it rational to automatically dismiss supernatural claims and/or explanations, or should such claims be seriously evaluated on their merits and the evidence for/against them? Is a presumption of naturalism a form of begging the question?

[Mithrae]

It almost sounds as if you're implying by contrast that 'natural' just means anything and everything we think we can explain, yes?

Not so much as I'm saying that in my observations, the supernatural may be invoked when one can't explain something through naturalistic means. This position doesn't deny the supernatural.

Once you've eliminated the impossible whatever is left, however improbable, must be the truth, right? Or alternatively, if there are no outstanding probabilities, there must be several valid possibilities. Some folk might say that 'invoked' is a somewhat loaded term to describe that reasoning process, and we've yet to discover what you mean by 'supernatural,' but fair enough I suppose.

Definitions are kinda subjective, where what is "cool" might even be "hot", so I won't refer, like I normally do, to Merriam-Webster, or other dictionaries on this'n. Some consider a god to be an otherwise "natural" part of nature / the universe / whatever. I don't.

The observer is asked to consider what they deem natural, and if my use of the term fits their understanding.

Of course Mithrae would be perfectly within his rights to offer a definition for us all to consider.

I can think of four, but as a basis for a useful concept of the 'supernatural' only one really seems to make sense: The one I gave above, essentially. 'Natural' basically means the normal way we see things happening and the 'supernatural' is how we describe stuff we don't see much (if at all). Merriam-Webster's definition 8:
8a : occurring in conformity with the ordinary course of nature. . . . c : having a normal or usual character


A second option, linked with your comments about explaining stuff through naturalistic means, essentially equates the natural with the scientific understanding of the world. This is philosophical naturalism, and obviously it's building somewhat on the first definition. There could be a problem though. Ever heard a Christian claim that science assumes atheism or the like? I think a lot of atheists suffer from the same confusion. Explaining something in a way which is not within the broad range of scientific understanding violates the principles of methodological naturalism used by science, but that's not actually forbidden to us plebians. It's hardly meaningful to say "You aren't following methodological naturalism, so you're invoking the supernatural!"

Seems to me that with this view of naturalism, in order to claim that something is 'supernatural' you'd need to show how it violates present scientific understanding of the universe - and that will usually mean showing (or assuming) how it occurred. For example, replacing or repairing organic tissue which had been crucified and buried for some 36 hours is well beyond the scope of 21st century medicine, but to my knowledge it would not actually violate any scientific laws and it may well be that in centuries to come we'll develop that technology. With this view of naturalism, it seems that a presumption of naturalism regarding a bodily resurrection of Jesus would be wholly irrational, because we'd first have to assume that it occurred in such a manner as to violate our scientific understanding. What about a god? While it's beyond the scope of science, can we assume that all concepts of a divine being actually violate our scientific understanding? I rather suspect not. With this view of naturalism, the term 'supernatural' seems to become either largely useless or (more frequently) is incorrectly associated merely with not applying metholodogical naturalism.


Avoiding that problem, a similar third definition of naturalism would be more or less equivalent with physicalism. Merriam-Webster's definition 12 for 'natural':
12a : having a physical or real existence as contrasted with one that is spiritual, intellectual, or fictitious
Again, this builds on the first definition - we apparently see a physical world every day of our lives - and it does clearly delineate gods and ghosts as 'supernatural.' But that this view is essentially one giant assumption can be seen by comparison with the other philosophical monisms, idealism or neutral monism. It's also curious to note that things like vampires, being physical, might not be readily classed as 'supernatural' in this view.


So I reckon that as much as 'supernatural' is a useful term, essentially it has to come from that first definition: Stuff that lies considerably outside the range of normal human experience. If we phrase it as extraodinary claims require extraordinary evidence, a presumption of 'naturalism' might be reasonable with that view. But I think a lot of people don't really think too much about what they mean when they describe or dismiss things as 'supernatural' - what particular definition are they working with, and how valid it may or may not be.

But personally, I agree with those folk you mentioned: If there's a god, he's obviously part of the nature of reality, as are his actions. While it seems to be the corollary of the most (perhaps only) useful definition of 'supernatural,' I wouldn't define 'natural' as the range of normal human experience. It would simply be the nature of reality, which short of assumptions like physicalism we really don't yet know enough about to start being dogmatic. As such, 'supernatural' really seems to be a biased or loaded term more than anything else.

But, as you've noted, there'll probably always be people who don't feel compelled to adhere to methodological naturalism in their forming of opinions - and thus there'll always be people who describe their opinions as 'supernatural.'

[Student]

Logical possibility and equal probability

It seems to me, and I think this deserves to be emphasised, that for all intents and purposes if anything is possible then everything is equally probable.

Perhaps I have misunderstood your hypothesis but it occurs to me that while anything may be possible, every “thing� does not have an equal probability of occurring, so everything cannot be equally probable.

For example, if I toss a coin, there is roughly an equal probability that the coin will land either heads up, or face up. However there is a third* possibility, i.e. that the coin will land on its edge. A coin landing in its edge is not impossible but highly improbable, significantly less probable than it landing either face or tails up. So a coin landing on its edge is not equally probable. (*and several more if anything is possible)

No doubt I’m mistaken, but I suspect that a system, where anything is possible and everything is probable, might require a phase space with infinite degrees of freedom / infinite dimensions. Every possible state of the system requires a combination of values of the system's parameters, so the system would have to be quite big. Not that infinity is improbable in a system where anything** is possible.

(**Even in a phase space with infinite degrees of freedom / infinite dimensions toast can only ever land jam side down.)

[Mithrae]

Logical possibility and equal probability

It seems to me, and I think this deserves to be emphasised, that for all intents and purposes if anything is possible then everything is equally probable.

Perhaps I have misunderstood your hypothesis but it occurs to me that while anything may be possible, every “thing� does not have an equal probability of occurring, so everything cannot be equally probable.

For example, if I toss a coin, there is roughly an equal probability that the coin will land either heads up, or face up. However there is a third* possibility, i.e. that the coin will land on its edge. A coin landing in its edge is not impossible but highly improbable, significantly less probable than it landing either face or tails up. So a coin landing on its edge is not equally probable. (*and several more if anything is possible)

No doubt I’m mistaken, but I suspect that a system, where anything is possible and everything is probable, might require a phase space with infinite degrees of freedom / infinite dimensions. Every possible state of the system requires a combination of values of the system's parameters, so the system would have to be quite big. Not that infinity is improbable in a system where anything** is possible.

(**Even in a phase space with infinite degrees of freedom / infinite dimensions toast can only ever land jam side down.)

lol True enough. Not a Terry Pratchett fan perchance? He even mentions the coin thing in one of his books.

I wouldn't be foolish enough to say it's a particularly well-developed hypothesis, and your question gave me plenty of food for thought on my walk home from work. But without straining my little head too much, I suppose the answer would be that it's true that there is not an equality of probability in our observations - even within the well-established parameters of human experience we know that people often see what they expect to see.

There is a hypothesis - identifiable in or extrapolated from (among others) Christian and Buddhist thought, Napoleon Hill's self-help classic Think and Grow Rich and even Star Trek: Next Generation - that the parameters by which we define our conception influences our perceptions. Or in more mundane terms, if you actually have the faith to do so you can move mountains. To no small extent, this could go back to whether the nature of the universe is physical, or mental, or some combination of the two (or even 'substances' which we can't really understand or define).

In short since we expect the coin to land on heads or tails, that's what it does. Is that view falsifiable? How much 'expectation' will weigh the possibilities in any given direction? Might a pair of scientists observing a test of the 'supernatural' constitute enough doubt as to tarnish the results? Doesn't really matter: That's just one of the possible reality-scenarios which might account for why a coin generally lands heads or tails and why it might not be a significant indicator of the actual nature or probabilities of that reality.

[Goat]

Logical possibility and equal probability

It seems to me, and I think this deserves to be emphasised, that for all intents and purposes if anything is possible then everything is equally probable.

Perhaps I have misunderstood your hypothesis but it occurs to me that while anything may be possible, every “thing� does not have an equal probability of occurring, so everything cannot be equally probable.

For example, if I toss a coin, there is roughly an equal probability that the coin will land either heads up, or face up. However there is a third* possibility, i.e. that the coin will land on its edge. A coin landing in its edge is not impossible but highly improbable, significantly less probable than it landing either face or tails up. So a coin landing on its edge is not equally probable. (*and several more if anything is possible)

No doubt I’m mistaken, but I suspect that a system, where anything is possible and everything is probable, might require a phase space with infinite degrees of freedom / infinite dimensions. Every possible state of the system requires a combination of values of the system's parameters, so the system would have to be quite big. Not that infinity is improbable in a system where anything** is possible.

(**Even in a phase space with infinite degrees of freedom / infinite dimensions toast can only ever land jam side down.)

Actually, there is a forth possibility for flipping a coin. You have a machine that very precisely controls the factor which influences which side it lands, and the landing of which side the coin lands on is predetermined.

[JoeyKnothead]

From Post 31:

Mithrae, I 'preciate your taking the time and offering me some great new data here. I hope to employ these new definitions and notions into my thinking, even if I may argue against some of what you say...

Once you've eliminated the impossible whatever is left, however improbable, must be the truth, right?

Wrong. That'd be an argument from ignorance.

Or alternatively, if there are no outstanding probabilities, there must be several valid possibilities. Some folk might say that 'invoked' is a somewhat loaded term to describe that reasoning process, and we've yet to discover what you mean by 'supernatural,' but fair enough I suppose.

I'm not so sophisticated that my definition of supernatural'd be too far off from what most folks consider it. What is outside of nature is commonly considered supernatural (while I note you offer some legitimate alternative definitions here directly).

I can think of four, but as a basis for a useful concept of the 'supernatural' only one really seems to make sense: The one I gave above, essentially. 'Natural' basically means the normal way we see things happening and the 'supernatural' is how we describe stuff we don't see much (if at all). Merriam-Webster's definition 8:
8a : occurring in conformity with the ordinary course of nature. . . . c : having a normal or usual character

I think your definition fails, for our purposes, because it considers anything "not normal" to be supernatural. Some cats don't chase mice, does this mean they're supernatural?

A second option, linked with your comments about explaining stuff through naturalistic means, essentially equates the natural with the scientific understanding of the world. This is philosophical naturalism, and obviously it's building somewhat on the first definition. There could be a problem though. Ever heard a Christian claim that science assumes atheism or the like? I think a lot of atheists suffer from the same confusion. Explaining something in a way which is not within the broad range of scientific understanding violates the principles of methodological naturalism used by science, but that's not actually forbidden to us plebians. It's hardly meaningful to say "You aren't following methodological naturalism, so you're invoking the supernatural!"

Plenty fair. I'd add that the rules of this site allow for reasonable and logical explanations, regardless of how "scientific" they may be.

I note you expound on this, but I interrupt to add...

I seldom ask for "scientific" evidence, but ask for "plain old" evidence (not being condescending here, but read some of my OPs that challenge claims, and see that I seldom use the term "scientific" when presenting challenges). What often happens though is folks assume I'm asking for the scientific sort, when I'm not. On that though, I see most often the case is that what "non-scientific" evidence is presented fails (at least for me).

Seems to me that with this view of naturalism, in order to claim that something is 'supernatural' you'd need to show how it violates present scientific understanding of the universe - and that will usually mean showing (or assuming) how it occurred...

I'm not so keen on the "violates scientific understanding" angle, specifically because scientists have gotten it wrong before. I note however, they sure get a bunch of it right.

For example, replacing or repairing organic tissue which had been crucified and buried for some 36 hours is well beyond the scope of 21st century medicine, but to my knowledge it would not actually violate any scientific laws and it may well be that in centuries to come we'll develop that technology.

I'm reminded of the "heal amputees" argument, and I've heard tell of some powder placed on lost fingertips allowing the fingertip to grow back (I won't bother supporting this, expecting folks to see what I'm getting at...). With this in mind, who's to say a god didn't somehow interfere to have these scientists create this stuff? My position is that if we can't show a god is involved, then we should not make such a claim (as relates to site rules or debate in general).

If I thought a god was involved, and I was challenged, I'd just go on and state the reasons I feel that way, and folks accepting or rejecting my argument would be just that. So often though, when challenging the claims of theists, I'm met with a hail of incredulity for merely challenging a claim.

Often their arguments go straight to the "scientific", where I've never mentioned the word. What I take from this is that the "arguer" sub/consciously realizes how weak their claim, and their evidence for that claim is.

With this view of naturalism, it seems that a presumption of naturalism regarding a bodily resurrection of Jesus would be wholly irrational, because we'd first have to assume that it occurred in such a manner as to violate our scientific understanding.

While I think that's plenty fair on one level, on another level we should not deny that folks we see being dead remain dead. I'm not talking about a clinical definition of death, but the total cessation of bodily function.

I don't take to your line of argument here because it borders on the "it's possible". Some stuff, while possible, is so unlikely as to demand incredulity when it's claimed otherwise.

What about a god? While it's beyond the scope of science, can we assume that all concepts of a divine being actually violate our scientific understanding? I rather suspect not. With this view of naturalism, the term 'supernatural' seems to become either largely useless or (more frequently) is incorrectly associated merely with not applying metholodogical naturalism.

Actually, my amateur scientific understanding is that the concept of a god has some advantages for the adherent.

I don't buy into the argument that since science can't address the god issue, the issue should retain some merit. I contend that where evidence is lacking, conclusions should be challenged. On the various claims of god I've challenged, I've yet to see an argument that convinces me. I don't try the "if I reject it, so should you" deal specifically because I'm just smart enough to know I ain't smart enough.

I've seen folks who, for them, the conclusion is reasonable and logical, and where they freely express their 'evidence', I see that, for them, they have arrived at a reasonable and logical conclusion for themselves. My deal tends towards those who make claims, in debate, then become all aggravated when those claims are challenged. My contention here is that such folks sub/consciously realize how weak their conclusions are.

I think of cnorman18 here. I simply can not refute the existence of a god as he expresses it. His arguments are compelling, he's straight up when challenged, and he'll tell ya right away he may be wrong - while retaining his self confidence in thinking he ain't wrong. This, if only to me, shows a mind that is as sound as any - even if I personally reject his conclusions.

I then think of those who make claims about gods - expecting folks to act or think in a given fashion - who cringe at the very notion of being challenged on their claims. I contend, with all respect, that such folks are a bit unhinged. I say that while readily admitting I have no claim to sanity myself.

Avoiding that problem, a similar third definition of naturalism would be more or less equivalent with physicalism. Merriam-Webster's definition 12 for 'natural':
12a : having a physical or real existence as contrasted with one that is spiritual, intellectual, or fictitious
Again, this builds on the first definition - we apparently see a physical world every day of our lives - and it does clearly delineate gods and ghosts as 'supernatural.' But that this view is essentially one giant assumption can be seen by comparison with the other philosophical monisms, idealism or neutral monism. It's also curious to note that things like vampires, being physical, might not be readily classed as 'supernatural' in this view.

I can dig it. I think I don't use the term "supernatural" as much as maybe folks think I do. On challenging claims however, I reject folks offering as evidence "that which can't be shown", which is what the argument from the supernatural is, essentially.

"Here's my reasonable and logical explanation" is fine with me, and has changed my mind on some things, but so often when I challenge claims, I get into a big fuss about how unfair it is for me to even challenge a claim, on this, a site dedicated to debate.

So I reckon that as much as 'supernatural' is a useful term, essentially it has to come from that first definition: Stuff that lies considerably outside the range of normal human experience. If we phrase it as extraodinary claims require extraordinary evidence, a presumption of 'naturalism' might be reasonable with that view. But I think a lot of people don't really think too much about what they mean when they describe or dismiss things as 'supernatural' - what particular definition are they working with, and how valid it may or may not be.

I'm not so keen on that definition, though I understand its utility.

But personally, I agree with those folk you mentioned: If there's a god, he's obviously part of the nature of reality, as are his actions. While it seems to be the corollary of the most (perhaps only) useful definition of 'supernatural,' I wouldn't define 'natural' as the range of normal human experience. It would simply be the nature of reality, which short of assumptions like physicalism we really don't yet know enough about to start being dogmatic. As such, 'supernatural' really seems to be a biased or loaded term more than anything else.

I grew up in Georgia, in the Bible Belt, so the term is not near as loaded to me. It's rather common, and understood to mean "outside of nature, even if impacting on it". Your definitions of course are as valid, but I tend to "go with what I know" when using what are to me common words and terms. I, maybe wrongly, assume folks know what I'm getting at.

But, as you've noted, there'll probably always be people who don't feel compelled to adhere to methodological naturalism in their forming of opinions - and thus there'll always be people who describe their opinions as 'supernatural.'

While I may appear to be a "methodological naturalist", I feel confident that I'm willing to accept a compelling argument, regardless of how much it goes against what I know.

[EduChris]

From Post 31

Once you've eliminated the impossible whatever is left, however improbable, must be the truth, right?

Wrong. That'd be an argument from ignorance.

Actually, it's an argument from logic--the very same logic routinely employed in every field of human interest and scholarship, including science.

[Student]

Logical possibility and equal probability

It seems to me, and I think this deserves to be emphasised, that for all intents and purposes if anything is possible then everything is equally probable.

Perhaps I have misunderstood your hypothesis but it occurs to me that while anything may be possible, every “thing� does not have an equal probability of occurring, so everything cannot be equally probable.

For example, if I toss a coin, there is roughly an equal probability that the coin will land either heads up, or face up. However there is a third* possibility, i.e. that the coin will land on its edge. A coin landing in its edge is not impossible but highly improbable, significantly less probable than it landing either face or tails up. So a coin landing on its edge is not equally probable. (*and several more if anything is possible)

No doubt I’m mistaken, but I suspect that a system, where anything is possible and everything is probable, might require a phase space with infinite degrees of freedom / infinite dimensions. Every possible state of the system requires a combination of values of the system's parameters, so the system would have to be quite big. Not that infinity is improbable in a system where anything** is possible.

(**Even in a phase space with infinite degrees of freedom / infinite dimensions toast can only ever land jam side down.)

Actually, there is a forth possibility for flipping a coin. You have a machine that very precisely controls the factor which influences which side it lands, and the landing of which side the coin lands on is predetermined.

If you re-read my post you will see that I acknowledge more than three possibilities = (*and several more if anything is possible) . Another possibility is that the coin never descends - we might toss the coin in zero gravity; yet another possibility is that it encounters an "anti-coin" and the pair mutually annihilate. In a system where anything is possible everything can happen even though the probability is vanishingly small. You only have to wait long enough for the next anomaly to come along.

[Mithrae]

From Post 31:

Mithrae, I 'preciate your taking the time and offering me some great new data here. I hope to employ these new definitions and notions into my thinking, even if I may argue against some of what you say...

Likewise I tend to learn a lot more when I have to consider the reasons I disagree with parts of what someone says, than when I limit my options to simple agreement or demanding proof.

Or alternatively, if there are no outstanding probabilities, there must be several valid possibilities. Some folk might say that 'invoked' is a somewhat loaded term to describe that reasoning process, and we've yet to discover what you mean by 'supernatural,' but fair enough I suppose.

I'm not so sophisticated that my definition of supernatural'd be too far off from what most folks consider it. What is outside of nature is commonly considered supernatural (while I note you offer some legitimate alternative definitions here directly).

I can think of four, but as a basis for a useful concept of the 'supernatural' only one really seems to make sense: The one I gave above, essentially. 'Natural' basically means the normal way we see things happening and the 'supernatural' is how we describe stuff we don't see much (if at all). Merriam-Webster's definition 8:
8a : occurring in conformity with the ordinary course of nature. . . . c : having a normal or usual character

I think your definition fails, for our purposes, because it considers anything "not normal" to be supernatural. Some cats don't chase mice, does this mean they're supernatural?

If every decade or two we saw someone coming back to life a few days after death, we probably wouldn't consider that supernatural either. Our concept of "what is outside of nature" is based exclusively on what we (as individuals and as cultures) have observed of it. I've suggested in the threads What does 'super-natural' mean and The alleged resurrection of Jesus that neither ghosts, nor gods, nor resurrections, nor predictive prophecy necessarily violate any laws of nature. But even most Christians would call the latter two at least 'supernatural,' because they're far more removed from common experience (or our generally-observed 'nature' of reality) than cats which don't chase critters.

Seems to me that with this view of naturalism, in order to claim that something is 'supernatural' you'd need to show how it violates present scientific understanding of the universe - and that will usually mean showing (or assuming) how it occurred...

I'm not so keen on the "violates scientific understanding" angle, specifically because scientists have gotten it wrong before. I note however, they sure get a bunch of it right.

Agreed on both points. It seems you would agree that this isn't a good way of defining the 'natural' or the 'supernatural.' My point below was also about that way of defining it, but I'll comment regardless...

With this view of naturalism, it seems that a presumption of naturalism regarding a bodily resurrection of Jesus would be wholly irrational, because we'd first have to assume that it occurred in such a manner as to violate our scientific understanding.

While I think that's plenty fair on one level, on another level we should not deny that folks we see being dead remain dead. I'm not talking about a clinical definition of death, but the total cessation of bodily function.

I don't take to your line of argument here because it borders on the "it's possible". Some stuff, while possible, is so unlikely as to demand incredulity when it's claimed otherwise.

As I'm fond of mentioning, the notion that my body's volume consists mostly of nothing could be considered so absurd as to demand incredulity. My reason for accepting the notion is not because I've seen any evidence that it is so, but because various books and sites have claimed that this is how atoms are. I have no way of knowing whether any of those people have actually seen an atom of course, and in fact I'd suggest that very few people (and perhaps none of the sources I've consulted) have seen an atom at all. Ultimately, I accept the claim not because of any prevalence of observation against absurdity or unlikelihood, but simply based on a cultural respect for the authority of science.

What about a god? While it's beyond the scope of science, can we assume that all concepts of a divine being actually violate our scientific understanding? I rather suspect not. With this view of naturalism, the term 'supernatural' seems to become either largely useless or (more frequently) is incorrectly associated merely with not applying metholodogical naturalism.

Actually, my amateur scientific understanding is that the concept of a god has some advantages for the adherent.

I don't buy into the argument that since science can't address the god issue, the issue should retain some merit. I contend that where evidence is lacking, conclusions should be challenged. On the various claims of god I've challenged, I've yet to see an argument that convinces me. I don't try the "if I reject it, so should you" deal specifically because I'm just smart enough to know I ain't smart enough.

But isn't that the whole point? We have no valid objective means by which to address the god-question (to the extent that science is valid and objective, of course), so theists naturally object to those who suppose that atheism should be considered a default position until proven otherwise. If we have no valid objective means to address the question, then either view holds similar merit.

But as I've mentioned above, even some of the views which I accept are not based on any valid objective evidence which I've seen, and I'd suggest the same is true for everyone. The scope of human knowledge is great enough these days that there's probably not a single person who has personally acquainted themselves with even a tenth of the evidence for it all. We all accept many things on other people's say-so, based largely on the presumption that if it were wrong it would be widely challenged.

Avoiding that problem, a similar third definition of naturalism would be more or less equivalent with physicalism. Merriam-Webster's definition 12 for 'natural':
12a : having a physical or real existence as contrasted with one that is spiritual, intellectual, or fictitious
Again, this builds on the first definition - we apparently see a physical world every day of our lives - and it does clearly delineate gods and ghosts as 'supernatural.' But that this view is essentially one giant assumption can be seen by comparison with the other philosophical monisms, idealism or neutral monism. It's also curious to note that things like vampires, being physical, might not be readily classed as 'supernatural' in this view.

I can dig it. I think I don't use the term "supernatural" as much as maybe folks think I do. On challenging claims however, I reject folks offering as evidence "that which can't be shown", which is what the argument from the supernatural is, essentially.

"Here's my reasonable and logical explanation" is fine with me, and has changed my mind on some things, but so often when I challenge claims, I get into a big fuss about how unfair it is for me to even challenge a claim, on this, a site dedicated to debate.

I think you'll find that any claim about details of reality is included with "that which can't be shown" on a debate forum - the best we might do is point people to sources which make those claims. You can't show me that the earth orbits the sun, or even show me that my computer desk exists.

While I haven't personally seen anyone getting into a big fuss about you challenging claims, if that were so I think it would show more than anything the huge amount of shared presumptions and context which the claimant and you have in common. The authority of science and the primary validity of empirical observations being the most obvious ones, though reference to a 'scholarly consensus' in non-scientific fields like biblical criticism often provides a background to religious debates also.

For example, if a Christian claims that Isaiah 45:1 is evidence regarding God because it prophecied the actions of the Persian king Cyrus nearly 200 years before his reign, the standard response is simply that 'scholars' agree it was written after Cyrus' actions (and based largely on the fact that it mentions Cyrus' actions). Or, alternatively, to demand 'evidence' that it was written 200 years before the reign of Cyrus; the presumption being that it probably wasn't, and the texts' own claim to that effect being considered invalid. That's not to say that you have personally been involved in that kind of discussion, but I imagine that a lot of folk who think debate forums are fun already have some decent idea about how discussions might generally proceed.

In my experience, often many amongst both theists and non-theists don't have the words to describe it, but what they're really arguing about are the fundamental presuppositions about the relative validity of their sources for knowledge. "There's no evidence for miracles" really just tells us that the claimant has not yet seen any miracle claims which, in their opinion, have been validated by sufficient evidence to warrant belief. So if they ask for evidence or confirmation of such claims, even a theist who's seen the blind walk and the lame see would be somewhat justified in suspecting that the questioner's criteria for 'evidence' are likely to exclude from the get-go everything they have to offer.