In matters of knowledge and belief, everything is probability. They who do not understand this, will commit innumerable errors, and waste gobs of time arguing to no purpose. This is especially evident in debates over who holds the burden of proof in any given matter, which debates will go nowhere and shed no light on anything, if they don’t frame what’s being debated as really a debate over what the probability of the disputed claim is, and why.
By which we mean epistemic probability. Not some objective or cosmo-Platonic or physical probability, but the probability that the position we are taking (whatever it is) is true given the information we have at the time we take that position. Physical probabilities have a relationship to epistemic probability, but it is not direct (see my discussion in Proving History, index “probability,” but especially pp. 23-26 and 266-75). But since every position logically entails an epistemic probability, every position entails a positive assertion.
And that means every position, whether assertion or rejection, even ambivalence or uncertainty. All is just an assertion of a probability. Every party to every debate over any matter of fact is making a positive assertion about a probability. Everyone. So anyone who thinks they are making a meaningful distinction worth arguing over when they claim things like “you can’t prove a negative” or “they who make a claim always bear the burden of evidence” is simply wrong. Apart from distinctions of degree, there is no meaningful difference between a denial or a “mere lack of belief,” or between either of those and the assertion of a contrary belief. Every single possible position with respect to any claim whatever, is affirming a probability. And thus every position is a positive position. Every position is “making a claim.” Every position is asserting a belief about something. Even agnosticism.
Disbelief vs. Null Belief
I’ll demonstrate shortly that every position is asserting a belief, whether it’s a denial, an affirmation, or even an expression of complete uncertainty. Every position is a belief. Every belief corresponds to a claim. But before we get to that, two more misunderstandings must be averted.
First, that fact, that every belief-state entails an affirmation of a probability, is the case even if that belief was literally just formed as soon as the debate was engaged. Most things we have no beliefs about until we think of them, and upon thinking of them (such as by being asked to), we evaluate what we believe upon encountering that consideration. But that is not merely encountering a claim contrary to some status quo (of “disbelief,” let’s say). Because when we have no belief, there is no status quo. There is no disbelief in what we’ve never considered. Such a thing is logically impossible. We can only form beliefs upon evaluation of the data informing a belief. And there is no difference in such an evaluation between affirming or doubting what we’ve been asked to consider: both are taking a position, both are making a claim. Both therefore bear the burden of evidence.
This may rankle some, and confuse others. But it will become undeniably clear by the time you finish reading here.
The Fallacy of Ignoring Priors
However, that fact does not give safe harbor to those who want to beat people over the head with it. Because many times, those who gloat that everyone bears the burden of proof, ignore the fact that a substantial burden has in fact already been met—in background knowledge. This is the fallacy of ignoring the priors. “Priors” meaning the probability already entailed by our background knowledge (often represented by “b” or “k” in a Bayesian equation). Every claim has a prior probability. Every claim. Both positive and negative; both certain and uncertain.
I have demonstrated elsewhere that every debate over any claim to fact is ultimately Bayesian, and that no other means of justifying the epistemic probability of a claim is valid that does not simply recapitulate, approximate, employ, or reduce to Bayes’ Theorem (see Proving History, pp. 106-14; with also pp. 97-106). Background evidence is evidence. So there is simply no avoiding the fact that already-considered background information already entails a probability for any claim’s truth. And we call that a prior probability.
When someone is given some “new” information (meaning, new to them, which can simply be something they never considered before, or even entirely new data), the question then becomes how much or in what way that new information changes, or “updates,” that prior probability. You then have a “posterior” probability: the probability that a claim is true given all the information you have; which must include not just background information (“b”) but also anything that’s just been added to it or called to your attention (which often gets designated with “e” in a Bayesian equation). Those two sets of data, b and e, together must encompass all knowledge, all data, all information, all evidence available to you. Bayes’ Theorem then dictates what probability is then entailed thereby.
And what we learn from this fact, is that all arguments over any claim to fact, are really just arguing over three numbers. In fact, sometimes, the dispute is solely over one lone number, a single probability, as often the parties to a debate will agree (or concede agreement) on the other two. Those three numbers are the likelihood of the new evidence on the claim being true, the likelihood of that same evidence on the claim being false, and the prior probability of that claim being true—or false, since each, the prior probability of it being true and the prior probability of it being false, is the logical converse of the other and therefore only one number describes both. Which is why all negation is assertion. Saying a claim has a low prior, is literally synonymous with saying it’s negation has a high prior. Either way, you are making a positive assertion. (See my old article Proving a Negative for a more colloquial discussion of this mathematically unavoidable fact.)
I won’t go into the mechanics of Bayes’ Theorem further here. Apart from my book Proving History, which goes into considerable detail about how Bayes’ Theorem works and how to apply it, I have also written numerous helpful blog articles, if you want to learn more about it. Here, the principal point is that there is always a prior probability for every claim—even if it’s 50%, such as when we have no prior information bearing on a claim’s probability (see “If You Learn Nothing Else“). And this means, very often, the burden of evidence has already been met. Even before any debate is engaged. And it is the one who claims to be able to overthrow that existing status quo who then bears “the burden of evidence.” Because the denier has already met their burden. So overcoming that requires taking up the burden anew.
I’ve already made this point repeatedly about the historicity of Jesus, for example. Contrary to what many overly enthusiastic atheists will say on the internet, historians who affirm Jesus existed do not bear the burden of evidence. Because the centuries-long academic consensus that Jesus existed entails having met a prima facie burden of evidence. In other words, the background evidence establishing that consensus already meets a requisite burden of evidence for the consensus position. There is a status quo, and it is (at least ostensibly) based on evidence. If someone wishes to challenge that consensus, then the burden of evidence lays now on that challenger to prove the consensus is in error; that the evidence that formed it either does not exist, hasn’t been soundly interpreted, or has other explanations that are as good or better; or to present evidence against that consensus, that the consensus ignored or overlooked.
And so on. In any event, a burden must be met. Because the background information already constitutes meeting a burden of evidence for the affirmative. Therefore the negative now bears the burden of evidence. Hence I bore the burden of evidence of proving doubt was warranted, and met that burden under peer review in On the Historicity of Jesus (which now those who wish to maintain the consensus should have to refute before continuing to affirm the consensus position). Even if we wish to argue that the background evidence the previous consensus was based on has been misused to generate unwarranted confidence, we bear the burden of showing that. Even a claim that the consensus is fraudulent (that it wasn’t based on evidence and thus hasn’t met a burden of evidence) requires meeting a burden of evidence. Because it is still a positive claim about the evidence. (See my articles On Evaluating Arguments from Consensus and Arguing Jesus Didn’t Exist Should Not Be a Strategy, and my discussion of evidential burden in Proving History, pp. 29-30 [“Axiom Six”].)
The same holds for atheism. Atheism has already met a basic prima facie burden of evidence. Background information already entails gods have extremely low prior probabilities. And has long done so, for decades if not centuries now. Indeed this is true for anything supernatural at all. (See my articles Defining the Supernatural and Defining the Supernatural vs. Logical Positivism, but also my extensive discussion in Sense and Goodness without God, Part IV, “What There Isn’t,” particularly section IV.1.1.7 on the burden of evidence; and my more formal discussion of evidential burdens in Proving History, index “smell test”).
It is therefore incumbent now on anyone who wishes to still affirm gods exist to bear the burden of evidence proving it. It is invalid to say atheists still bear the same burden now. Because they’ve already met that burden. The status quo is: no gods have been found, and vast amounts of background evidence leave all gods with extremely low priors. Therefore anyone who wishes to up those priors, bears the burden of presenting data that does that. Absent which, we can go on doubting gods every bit as much as we doubt magic, faeries, gremlins, or psionics. No further evidence need be collected to justify that.
The Burden of Confusion
The fallacy of ignoring priors will sometimes lead to people talking past each other: one side overlooking that their priors are already based on evidence; the other side overlooking that there even are evidence-based priors at all. As a result, one side will argue that just saying atheists bear the burden of proof helps theists to deploy the fallacy of burden shifting, while another side will argue that even atheists have to be able to give reasons for why they are an atheist; and each will think they are arguing against each other, when in fact both are correct.
For example, Steve McRae has been debating several folks on this for a while, including most relevantly on an episode of DE/Converted hosted by Arael Avenu. McRae unfortunately adopts (or occasionally slips into) a dysfunctional epistemology (in which the only possible belief-states are “100% true” or “100% false,” which frequently contradicts psychological fact and the requirements of logical utility), but that’s a debate for another time. In respect to burden of evidence, McRae focuses on the analytic fact that all beliefs (I would say all epistemic probabilities) require evidence and therefore every assertion bears a burden of evidence in a fundamental sense—which simply means: we must all have reasons, and good reasons, for whatever position we take, positive or negative, if our position is to be in any sense valid. Which is correct. But McRae then obsesses on this to the point of overlooking that this being analytically true is moot when vast amounts of background evidence have already met that required burden. He is stuck on the fallacy of ignoring priors. (His occasional slip into a dysfunctional and unscientific non-probabilistic epistemology may be responsible for this.)
McCrae needs to acknowledge that a low prior probability for God is already entailed by our background knowledge, thus settling the burden now on theists, because atheists have already met theirs; while his opponents need to acknowledge that we should be able, when called upon, to give an accounting of this background knowledge, by which we already reached a conclusion of low probability for the existence of any gods. That’s what McRae means by meeting a burden of evidence: simply explaining what already convinced us the probability is low, when someone asks us to. But it still follows that anyone who wants to change that probability, now bears the burden of evidence. Atheists no longer do.
McRae’s opponents are also trying to correctly point out that if someone has not met a burden of evidence requisite to believe a claim, then no further burden of evidence need be met to reject it. As Christopher Hitchens famously put it, “That which can be asserted without evidence can be dismissed without evidence.” In probabilistic terms, if you have not presented any evidence your claim is epistemically probable, I am by that fact alone warranted in concluding it is, so far as I know, not epistemically probable. Because were I warranted in thinking that, by definition it would be upon seeing evidence warranting it. Ergo, if I have no evidence, I have no warrant.
An epistemic probability is by definition P(h|e.b), which symbolically translates as “the probability of h given e.b,” where h is the claim (which can be positive or negative, an assertion or a denial) and e.b is the combination of e and b (as I mentioned before), the sum total of all information (all evidence) available to you. P(h), the probability we would be right to assert h is true, follows necessarily from what is in e.b.
So if there is nothing in e.b. that makes P(h|e.b) high, then by definition we have no warrant to believe that P(h|e.b) is high. We need meet no other burden to warrant that conclusion. The absence of evidence alone meets the requisite burden. Conversely however, we cannot simply assert P(h|e.b) is low, either, if nothing in e.b entails it is low. Which is McRae’s point. And he, like his opponents, is also right.
Thus, to assert the probability of h is low, does indeed require meeting a burden of evidence, in the sense that e.b must contain sufficient information to entail P(h|e.b) is low. But if there is nothing in e.b that makes it higher than 50% and nothing that makes it lower than 50%, then by definition the epistemic probability of h is 50%. Which means, so far as we know (“given what we know”), we would be as likely to be right as wrong if we asserted h was true.
This is why the claim “if you can’t refute it, it must be true” is a fallacy. It does not follow that the lack of evidence in e.b that P(h|e.b) is low entails that P(h|e.b) is high. If there is no evidence in e.b for either, then by definition P(h|e.b) is neither high nor low. It is therefore 50/50, which means, it is as likely to be true as false—so far as we know. New information could change that. But that’s what meeting a “burden of evidence” refers to: presenting evidence for P(h|e.b) being anything other than 50%. Atheists can do this from the contents of b alone. P(God|b), the prior probability of God, is already so low given b, that theists need to put some evidence in e that would change that. They are therefore the only ones the burden of evidence now falls upon. Because we’ve already met out epistemic requirements.
You’re Both Making Assertions about the Evidence
It is also the case that every denial entails an assertion, not merely as to a converse probability, but also as to a basic metaphysical fact about the contents of the world: that the evidence a claimant asserts proves their claim, either doesn’t exist, isn’t as described, entails something else, or was caused by something else. All of which are positive assertions about the evidence (and thus about what does and doesn’t exist).
The difference however is that one can validly say, for example, “any of a hundred other different things more likely caused that evidence” as a positive assertion that entails the claim is improbable and thus to be doubted or disbelieved. Which is a much more diffuse claim than “this evidence was caused by what I claim it was caused by.” This is what often leads to frustration or confusion about the burden of evidence. Denying a claim does not require as focused an assertion as affirming a claim. You needn’t “pick an alternative explanation” to be right; you can admit it could be any of many. But that should not disguise the fact that this is still making an assertion.
Hence to deny an assertion about what caused the evidence in question, you need merely affirm that there can be many alternative explanations of that same evidence, and that it is more likely one of them caused the evidence than the explanation being touted. Which does not, incidentally, require that any single one of those explanations is more likely than the explanation being touted. Although they may well be, it can also be the case that the sum of all their probabilities is the greater, even when no singular one of them is. As I noted once before using the example of the cause of Alexander the Great’s death:
in his critique of [atheist critic Michael] Martin, [Christian apologist Stephen] Davis suggests that even if “the probability of the falsity of [a hypothesis] H is .6,” i.e. 60%, it would still be rational to believe H if each of the only four other possibilities has a mere .15 or 15% probability of being true. This is unsound reasoning. In the scenario he describes, there would be a 60% chance that some one of the other explanations is true (which he labels A, B, C and D), so it would not be rational to believe H. What would be rational is to conclude that you don’t know which explanation is true.
For example, if Alexander died and the only options available were all natural causes except H, which was ‘murder’, then there would be a 60% chance that Alexander died of natural causes, and therefore it would not be rational to believe he was murdered. Though it would make sense in a gambling scenario to bet on H, that would only be the case if you had to bet, or could afford to lose. But history is not gambling. If you get to bet your life on A, B, C, D, or H, or not bet anything at all, in Davis’ scenario the rational choice would be to refrain from betting, since no matter which bet you placed, the odds would always favor your death. In such a case it would never be rational to say “I believe H will be a winning bet” even if it’s the best bet on the table. …
As far as sound historical argument goes, it would never be rational to say “I believe H is true” when you know H more probably than not is false.
Often these many alternatives are well understood but not stated. We all well know how evidence gets fabricated, distorted, misinterpreted, or caused by other things. So merely the fact that the alternatives are not stated, does not entail they are not being affirmed. To the contrary, affirming that the evidence does not entail the conclusion being touted, logically entails affirming that that evidence had some other cause (or does not exist, or some other positive assertion about it). Therefore, all negation is assertion. All doubt and disbelief entails a positive claim. It just might not be as reductive as affirming a specific description and explanation of the evidence; but it is still affirming that some description and explanation of the evidence exists that does not entail the conclusion being touted. Otherwise your denial could not be logically valid.
Atheism Overlapping Agnosticism
This also corrects common misunderstandings about the differences between atheists and agnostics.
What many people mean by “atheist” in common discourse is simply someone who is not a theist, which means, someone who does not believe any gods exist. Which only requires they conclude no god has a probability of existing of at least 50% or above. That means anyone who puts P(AnyGods) below 0.50 is an atheist in this sense. Which in turn means anyone who is an atheist in this sense is declaring that P(AnyGods) is below 0.50.
That’s how many people use and understand the words “atheist” and “atheism” in practice. But even this broadest of definitions still means atheists are making a positive claim: that P(God) < 0.50. That is a belief. Not merely the absence of a belief—which rarely exists in this case, since hardly anyone has never heard about or thought of gods nor been asked to consider whether gods exist. When it comes to considered matters, all “absences of belief” are actually positive beliefs in the low probability of that which is disbelieved. But then, that’s just colloquially what people really mean when they say they lack belief in a thing, and hence what they usually mean by “a mere absense of belief”: that they believe the thing in question has a low (or at least not appreciably high) probability of existing (or of being true, or whatever is being asserted of it). Only people who have never heard of gods nor ever thought of any actually lack all belief in the matter.
What we most commonly mean by “agnosticism” in colloquial discourse ends up being really just a probability conclusion for the doubted object (whether God, a historical Jesus, or that Trump hired prostitutes to urinate on a Moscow bed) that is too close to 50/50 to declare definite knowledge either way. One can be agnostic but lean toward belief, and thus be an agnostic theist, e.g. someone who concludes P(God) = 0.60 (or 60%). One can be agnostic but lean toward nonbelief, and thus be an agnostic atheist, e.g. someone who concludes P(God) = 0.20 (or 20%). One can be an agnostic and lean neither way and thus be completely undecided, which means someone who concludes P(God) = 0.50 (or 50%). Which includes everyone who concludes this value (of 0.50) lies within their margin of error, e.g. those who conclude P(God) = some value unknown to them except that it almost certainly lies, for all they know, between 0.35 and 0.55.
The old, original and formal definition of agnosticism (that knowledge regarding God’s existence is presently or even logically impossible) is almost entirely unknown to the general public and thus is almost never what anyone in regular discourse actually means by the term. If you want to be understood in common discourse with regular people, you can’t be using words in connotations they are unlikely to know. But even if you are a linguistic imperialist kicking against the goad of the inevitable march of history in transforming linguistic conventions, agnosticism in that formal sense is still just a subset of agnosticism in the more common, informal sense. So arguing over its definition doesn’t really get you anywhere anyway and is generally a waste of time.
You must unpack all belief states (positive and negative, believing and disbelieving, asserting and doubting) as simply an assertion of a probability. Which usually means in practice some range of probabilities, reflecting one’s confidence interval: that the probability must lie between A and B—when the available information entails you can’t know where between, but you know to a very high probability it is not outside that interval. And you must unpack all assertions about belief in just that way, because that’s what all belief-states logically entail—and there is no way to escape this (no matter how big a doofus you want to try to be).
Uncertainty, is simply an assertion about a probability. Doubt, is simply an assertion about a probability. Lack of knowledge, is simply an assertion about a probability. Disbelief, is simply an assertion about a probability. Denial, is simply an assertion about a probability. At most, what distinctions one might intend with such words, are merely of degree. “Doubt” often implies you are asserting a low but not very low probability, whereas “disbelief” often implies you are asserting a very low probability, and “denial” often implies you are asserting a much lower probability than even that. And so on. Likewise for belief, which also exists in varying degrees of certainty, and we may have various words we sometimes use for them. But whether we have a word for each distinction or not, every belief-state corresponds to an asserted range of probability for some claim. So every belief-state, whether of denial, doubt, belief, or certainty, entails a positive assertion, a claim.
A popular trend has also arisen that narrows the intended meaning of “atheism” in distinction to “agnosticism.” In this connotation they are semantically distinct in that, even colloquially, “agnosticism” often refers to the positive belief that the probability of a god is in some middling range, whereas “atheism” often refers to the positive belief that the probability of a god is definitely quite low (and thus not in a middling range).
Typically, agnosticism is used to refer to a type of atheism only in the broadest sense: those who assign a low probability to God; but now “agnostic” often means, more narrowly, those who assign a low probability, but not so low as to be confident enough to declare themselves atheists. By contrast, “atheist” is often understood to indicate one has concluded the probability of God is much lower than “agnostics” declare.
But it is still semantically possible for an agnostic to be a theist, if for example they assign a higher probability to God, but not so high as to be confident enough to declare certainty of that God’s existence. They are still typically classified as theists. They do, after all, have some belief there is a god. The converse is thus just as valid, that agnostic doubters of god are technically still atheists. Just not “hard” or “strong” atheists as the parlance would have it. But “soft” or “weak” atheists.
Of course it’s really analytically worse than that for anyone who wants to act the linguistic imperialist and try to deny what I’ve just said is a correct application of these words in real world discourse and practice. Because analytically, everyone (atheists, agnostics, and theists) are both atheists and agnostics simultaneously. Because there are always some gods everyone is an atheist regarding, and always some gods everyone is a formal agnostic regarding (see my old discussion in Atheist or Agnostic demonstrating this point).
The only thing that separates any of these folks at all is (a) whether they believe in at least one god (which means, that they conclude P(God) for at least one god is > 0.50) or, in the absence of that, (b) whether they believe at least one god has more than a marginal probability of existing (which means, that they conclude P(God) is for no gods > 0.50 but for at least one god > 0.10 or even higher). The latter group is what common practice has evolved to understand by and label with the word “agnostic.” While “atheist” has evolved in linguistic convention to more typically mean someone who meets neither condition (a) nor condition (b). But lexically, and still often enough, “atheism” as a word in many contexts includes those in condition (b), in parallel to that same word’s exclusion of those in condition (a).
So there is no point in arguing what these words mean, like whether “atheist” includes or excludes persons in condition (b), or whether “agnostic” refers only to a subset of those persons or all of them. Each does both, depending on how the word is being used, depending on context and the communicator’s intent. Same as most words.
Gods Are Already Improbable
As I already said, the prior probability for any god, as for anything supernatural, is already well established to be low. Background evidence has already met the burden of establishing that. Which is why theists bear the burden of evidence of disproving that now. And why atheism is now the only logically valid default position. It is not the default because it is the absence of a claim. It is the default because the historical parade of evidence has established it to be.
For example, when we doubt gods exist because we doubt disembodied minds even could exist (see, for instance, The Argument from Mind-Brain Dysteleology, The God Impossible, and The Argument from Specified Complexity against the Supernatural), the premise (that disembodied minds probably can’t exist) is based on extensive past knowledge in the matter. And the conclusion validly follows from the premise (if probably there are no disembodied minds, then probably there are no gods).
So the burden of evidence has already been met. Before we even show up to the debate. It’s not as if we just popped into existence, devoid of all background knowledge. If we had, we would not doubt the possibility of disembodied minds; we’d conclude instead that they had a 50/50 chance of being possible until we get more information, and thus would need to start learning what we can that pertains to the question—like getting up to speed on the basics of neuroscience; indeed, even on the fact that there was such a thing as neuroscience. But humans are rarely in such a condition. We don’t pop magically into existence in the middle of a debate devoid of any background knowledge. We come to any debate already packed with vast quantities of background knowledge.
The same goes for every other reason we doubt gods exist: it’s based on extensive background knowledge. The burden has already been met. Therefore theists bear the burden of evidence now. Not because they are the ones making a claim; for the atheists are making the very same claim, just with a different P. It’s thus not about who is making a claim. Rather, theists bear the burden of evidence because atheists have already met theirs. The prior probability of gods is low. If the theist wants to change that, to increase that P, they have to present some e (some evidence) that will do that. In the absence of which, the current default remains: the low prior, previously established by already-examined background data.
This is why Don McIntosh is simply wrong, when he attempts to rebut my old article about Proving a Negative. God’s existence has already been amply refuted; background knowledge already puts his prior probability in the dumpster (see, for example, my summaries in Bayesian Counter-Apologetics, my book Why I Am Not a Christian, and Part IV of my book Sense and Goodness without God; you should also note why turning God into a Cartesian Demon is never a valid rebuttal).
Indeed, my own article on Proving a Negative that McIntosh claims to be rebutting, already refutes his contrary assertions—he simply ignores what it actually says, and makes up a bunch of excuses for his god’s undetectability that I already demonstrated to be improbable. When we go back to the actual data, we don’t get the result he wants. So he has to ignore data to get it. But that data remains, and collectively it has already established gods have low priors. Thus anyone who wishes to restore that probability to anything respectable now bears the burden of presenting the needed data. And to do that, speculations aren’t data; no excuse for God is credible, if you have no evidence that excuse is probable. And McIntosh has no evidence any of his excuses are at all probable. Merely being possible is not enough (see my discussion of this fallacy in Proving History, pp. 26-29).
McIntosh is also wrong about how evidence works in more basic ways. For instance, he is wrong to claim we cannot justify concluding the existence of Vogons has a very low probability. Contrary to what he says, we do not have to check every corner of the universe, to estimate the highest credible probability of a coincidence between a ridiculous authored fiction and reality. Indeed, Vogons are probably even logically impossible, for the same reasons I show for Star Wars in The God Impossible. But even if they were probabilistically certain to exist, by virtue of the universe being infinite and infinitely configured (though the former is not certain, and the latter is not actually entailed by the former, and yet both are required for real Vogons to have a high probability), we can still show the probability that they exist anywhere near us is as near to zero as anyone cares that it be. Again, without “checking every corner of the universe.” And that’s just on background knowledge alone.
This is why it’s important to always convert every discussion of what does or doesn’t exist, what is or isn’t true, into a debate over a probability. Not of possibility. Not of “true or false.” But how probable. Because then we must ask why it’s that probability and not some other. McIntosh for instance would have immediately started to question his own thinking the moment he was forced to admit his own assertions entailed he believed there was a 50% chance Vogons existed. Exploring why that’s absurd, might hopefully have led him to a more coherent epistemology.
Reasonable discussion of debating the burden of proof can be found at Logically Fallacious and RationalWiki. But it always comes down to this: the “burden of proof” for any position semantically means “information that increases the probability of that position,” and usually not merely that, but “increases it above 50%,” or in fact higher still. Because epistemic probabilities only marginally above 50% still entail considerable doubt and uncertainty. After all, we don’t usually touch things that have only a 70% chance of not electrocuting us, so “70% safe” is not that great a probability. So when our probabilities are not high in either direction (e.g. not above 0.90 or even 0.999 nor below 0.10 or even 0.001), what we are quantifying is doubt, uncertainty, lack of knowledge—agnosticism. Hence, agnosticism, uncertainty, doubt, are still all positive assertions in their own right. They simply refer to probability assignments that are neither very high nor very low. But they still always assert something about the probability of a thing, such as (at the very least) that it is most likely neither very high nor very low.
And this means you can never simply argue the burden of evidence lies with “the one making a claim,” because everyone is making a claim. Disbelievers in any God, even colloquial agnostics about gods, are making as much of a claim about the existence of God as believers are. They are simply disputing what P(God) is. But every value for P(God) is as much an assertion as any other, and just as requiring of positive belief. Even a genuine “I don’t know” condition is simply the positive assertion that P(God) is 0.50 (or that one’s confidence interval for P(God) includes 0.50). Which requires as much justification as any other declared P.
However, this does not mean you can always claim “everyone always bears a burden of evidence.” Because very often, particularly in matters that have been widely discussed, investigated, and explored for ages, the expected (even if minimal) burden has already been met. It is met in our background knowledge. And for God the priors are thus already established to be low. And that means anyone who wants to raise that prior, is the one who bears the burden of evidence to do so. Atheists have already met their burden. It’s on theists now to overcome it. Or admit they can’t.