I. Burden of Proof in General

A burden of proof can be understood as an obligation to provide evidence, argument, or justification. It is a burden, because it is an obligation. It is a burden of proof, because what it requires is evidence, argument, or justification.

A person has the burden of proof for a claim when they have an obligation to provide evidence, argument, or justification for that claim. We can also say that a claim has the burden of proof when anyone who makes that claim has the burden of proof for that claim. Making a claim here includes either publicly asserting or privately believing the claim.

Burden of proof comes in degrees. The burden is heavier when more evidence, argument, or justification is required in order to fulfill the obligation. The burden of proof for making a claim can then be heavier or lighter than the burden of proof for denying that claim, but the lighter burden of proof still counts as some burden of proof.

Any obligation raises the question of what sanction is imposed when someone fails to fulfill the obligation.Footnote ¹ The sanction for a person who fails to carry a burden of proof in a legal trial is not a fine, prison term, or moral condemnation. Instead, a court’s sanction on someone who fails to carry a burden of proof is supposed to be an adverse verdict. However, courts sometimes find defendants guilty or liable when the burden of proof is not really met, such as when the judge or jury mistakenly believes that the burden of proof was met or disregards the legal standards of proof. The real sanction, then, is that the court is not justified in finding the defendant guilty or liable when the burden of proof is not met. This failure to be justified counts as a sanction because the person who is not justified wants or ought to be justified and is subject to criticism for not being justified.

The sanction for failing to meet a burden of proof in a public philosophical debate—such as in a publication, conference, or class—also concerns what is justified. A public speaker or author is not justified in stopping before giving an argument if they have not yet carried their burden of proof. Referees for a journal can legitimately ask the author to add further justification for their assumptions before publication. Audiences at a conference can dismiss a talk as inadequate when it did not meet the burden of proof. Instructors can give a student a bad grade for simply announcing their view without giving any reason to believe it when they have a burden of proof.

Although burden of proof is discussed most often in public contexts, many of the same basic issues arise when people privately ponder what to believe. When a lone philosopher is thinking about whether or not to believe in free will, for example, they ask themselves whether they need additional arguments for their assumptions and whether they are ready to believe in free will or deny it. They are not justified in drawing either conclusion yet if they have a burden of proof that they have not carried.

In such private reflections, the kind of justifiedness that is lacking is not institutional (as in law) or professional (as in public debates) but epistemic: a person is not epistemically justified in believing or stating a claim when they fail to carry a relevant burden of proof. Conversely, a person is justified in believing or stating a claim without any evidence if they do not have any relevant burden of proof. To say that a person has no burden of proof concerning a claim is then close to saying that the person is justified in taking that claim as a presumption, a default, self-evident, or an intuition that does not need any support from evidence or argument. Burden of proof is also related to an argument from ignorance, since “You cannot prove that my claim is false, so I am justified in making my claim” is fallacious if, but only if, the person who says it has a burden of proof for that claim.

Some critics might object that such epistemic requirements in private contexts should not be called burdens of proof, because burdens of proof are used only in public adversarial institutions to ensure that disputes get decided,Footnote ² whereas a private person can simply refuse to draw any conclusion and admit that they do not know. I agree that these contexts differ in relevant ways, and I do not want to argue about how to use the technical term “burden of proof.” What matters here is that, whatever others call them, what I call burdens of proof in law, public debates, and private reflection are all about whether a claim is justified in the absence of certain kinds of evidence or argument for it. This fundamental similarity is what leads me to call them all burdens of proof.

Still, as Schauer pointed out, who has the burden of proof and how heavy that burden is varies with context. The crucial question, then, is how to determine who has a burden of proof and how heavy it is in a particular context. To see how and why burden of proof is allotted, we will focus on the contexts of law and philosophy.

II. Burden of Proof in Law

Burden of proof in law involves several distinct (though related) issues. The burden of production (to justify having a trial or a jury deliberation) differs from the burden of persuasion (to justify a verdict). The issue of who has the burden is also distinct from the issue of how much burden they have. In criminal cases, for example, the legal system could put a heavy burden on the prosecution to prove guilt beyond a reasonable doubt and a lighter burden on the defendant to prove an affirmative defense (such as insanity, coercion, duress, entrapment, or self-defense) to a preponderance of evidence or with clear and convincing evidence.

How should these burdens be determined? In one sense, the answer is that the burden of proof is settled by existing statutes and precedents. That is not what I am asking. My question is how to determine what these statutes and precedents should be. This question asks not what the law actually says but, instead, how to determine where the legal system should place the burden of proof (and how much burden they should be obliged to carry).

One method appeals to bald intuition: Just ask yourself who should have to carry the burden of proof and how much. The problem with this method is that it leaves no way to check whether these intuitions are correct or to explain why one side has a burden of proof to a specific degree.

Another method is more pragmatic and consequentialist: Determine what is likely to happen in a legal system and a society when the burden of proof is placed on one party instead of another or when the burden has one weight instead of another. The question is then about comparing the probabilities and the severities of various harms to various people from various burdens.

For example, why should prosecutors be required to prove guilt beyond a reasonable doubt? One answer is that this target and degree of burden of proof is obvious intuitively. But it isn’t. We have become used to it, but tradition by itself does not make it correct. The pragmatic answer instead refers to the effects on our legal system or community of redirecting this burden of proof. If defendants were given the burden of proving their innocence, then we would live in fear of being prosecuted for all manner of crimes. How could you prove that you did not sneak out in the middle of the night and rob your neighbor? Moreover, prosecutors would have more power to hassle and convict their enemies without having to prove anything, so nefarious politicians could solidify their power too easily. They would need only to charge some crime that their opponents could not disprove.

This pragmatic approach also helps to explain why it is not prosecutors but defendants who have the burden of proof in some cases. If a defendant claims to have been coerced by an unknown stranger, they usually are required to prove this “affirmative” defense. Why? Presumably because few defendants are coerced, and it would be too hard for prosecutors to prove that a defendant was not coerced. The same holds for other affirmative defenses, including insanity, duress, entrapment, and self-defense.Footnote ³ As a result, too many criminals would get away with their crimes if we placed a burden on prosecutors to disprove these affirmative defenses.

This pragmatic approach to burden of proof was developed in detail by Schauer.Footnote ⁴ It fits perfectly into Schauer’s more general insights that law is about force and the distribution of power.Footnote ⁵ The need to consider effects of general rules governing burden of proof also aligns with Schauer’s emphasis on rules in law.Footnote ⁶

Schauer emphasizes that which rules about burden of proof are justified varies with context and the values at stake in that context. His point is not just that different burdens of proof are appropriate in criminal versus civil law but also that different burdens of proof can be appropriate inside versus outside of law. One does not have to prove beyond a reasonable doubt that a person is guilty of embezzlement (or child molestation) in order to be justified in refusing to hire that person as one’s accountant (or babysitter). As Schauer puts the point, “In some contexts and for some purposes, weaker evidence may be good enough.”Footnote ⁷

III. Burden of Proof in Philosophy

Because burden of proof varies with context, we need to consider contexts separately. I am a philosopher, so I wonder who has a burden of proof in believing or asserting—two ways of making—a philosophical claim. When Schauer wrote, “the burden of proof is an idea of pervasive importance and common confusion,”Footnote ⁸ he did not have philosophy in mind, but his point applies to philosophy. Indeed, it applies in multiple ways.

Some philosophers assume that the burden of proof applies only to what people assert explicitly or implicitly in public settings. In informal conversations, classroom discussions, or written or spoken professional debates, for example, there might be some kind of rules governing when an individual may or must provide explicit reasons for their claims, what they are allowed to take for granted, which kinds of objections may be raised, and what standards determine grades in the classrooms and winners in the debates. These rules involve one kind of burden of proof, which can be called public burden of proof.

My topic here is broader. The kind of burden of proof that concerns me is also relevant when a philosopher is all alone thinking about an issue and trying to figure out what is true or what to believe without telling anyone else. Even if the philosopher reads what others wrote, they are not trying to beat anyone but only to determine which position they are justified in adopting. This private context of deliberation matters to me here. For simplicity, I will often talk about whether one side in a debate has a burden of proof, but all I mean is that a person who makes the claim associated with that side has a burden of proof. The crucial issue here is whether a philosopher who is deliberating about that claim needs evidence or argument for that claim in order to be justified in believing it or in denying it.Footnote ⁹

In this sense, many issues in philosophy rest on who has the burden of proof. Here are a few classic examples. These appeals to burden of proof should seem familiar to those who have read or heard discussions of these issues or who have simply thought about them. It should also be clear that these burdens are hard to carry:

1. (1) Philosophy of Religion: An all-good, all-powerful God is incompatible with any evil that is not necessary for any adequately compensating good.Footnote ¹⁰ Atheists claim that theists have the burden of showing, for each apparent evil (such as Tay-Sachs disease), which good that evil is necessary for and why this good is adequate as compensation. Theists reply that atheists have the burden of proving that some evil is not necessary for any adequately compensating good, including a good effect known only to God.

2. (2) Philosophy of Mind: Dualists assume that physicalists have the burden of showing that all aspects of our minds, including subjective qualia, are reducible to something physical and what they are reducible to. Physicalists reply that dualists have the burden of proving that some mental states are not reducible to anything physical, including physical states that scientists have not yet identified.Footnote ¹¹

3. (3) Epistemology: Skeptics argue that their opponents have the burden of proving that we know something and what it is that we know.Footnote ¹² Commonsense philosophers reply that skeptics have the burden of proving that we do not know any of what seems obvious, such as that all live humans have heads.Footnote ¹³

4. (4) Metaphysics: Hard determinists assume that proponents of free will have the burden of showing which decisions are free and how they can be free. Defenders of free will reply that anyone who denies all free will has the burden of showing that no act meets the requirements for free will, including horrible atrocities that deserve punishment.Footnote ¹⁴

5. (5) Ethics: Many consequentialists claim that every agent who can but fails to prevent any harm to anyone anywhere has the burden of showing that preventing it would require sacrificing something of comparable moral worth.Footnote ¹⁵ Deontologists respond that consequentialists have the burden of showing that there are no limits on these demands, not even to give a small birthday present to one’s child.Footnote ¹⁶

6. (6) Meta-Ethics: Expressivists assume that moral realists have the burden of explaining how objective moral facts or properties fit into the natural world (with location and causation).Footnote ¹⁷ Moral realists reply that expressivists have the burden of showing how moral judgments fit into conditionals and negations (such as the negative claim that abortion is not immoral) if they only express non-cognitive attitudes.Footnote ¹⁸

In these classic philosophical disputes and many more, each side assumes that the other side has the burden of proof and that they do not. When a philosopher in private deliberates about which claim to believe, the result of their deliberation will depend on which claim they put the burden of proof on.

It might not seem necessary for a philosopher to reach any conclusion or take any position, and then they might not need to assign any burden of proof. It might even seem harmful to reach a conclusion on a philosophical issue if doing so restricts future inquiry without justification. However, many philosophers and non-philosophers do want to decide what to believe. They need to assign burden of proof somewhere. There can also be practical costs to suspending belief on some philosophical issues. In ethics, if one suspends belief between consequentialism and deontology, this will make it harder for one to decide how to act in some important situations where these two moral theories conflict. In philosophy of mind, if one suspends belief about dualism, then one cannot consistently cite physicalism to argue against life after death or against other non-physical entities, such as ghosts. In philosophy of religion, suspending belief in God can alienate relatives and land a non-believer in hell, according to some theists. Thus, we often need to take a philosophical stand even in our everyday lives. For that, we need to place the burden of proof somewhere.

The point is not that all philosophers must accept a single method. There might be many ways to carry the burden of proof with many kinds of evidence. Despite this pluralism, every method needs some way to determine when a claim does or does not need to be supported by evidence of whatever kind the method provides. That is, in effect, to determine when there is or is not a burden of proof.

How can we determine which claim has the burden of proof? If the burden of proof is assigned solely on a case-by-case basis, there will be no principled, stable, or justified way to settle who or what has the burden of proof. To support placing the burden of proof on one claim but not another, philosophers need some general rule for allocating burden of proof in a wider range of cases. The fact that the rule works for many other cases in addition to the current issue suggests that the rule was not cherry-picked simply to favor one claim over the other. General rules like these are an essential part of any systematic method in philosophy.

A regress problem seems to arise if we need to justify our rules about which side has the burden of proof for philosophical beliefs, and if we cannot be justified in accepting any such rules unless we also accept and can justify higher-order rules about who has the burden of proof for accepting or denying rules about who has the burden of proof, and if this requires even higher order rules, and so on forever. However, this regress might be avoided if the same rules about burden of proof also apply to whether someone is justified in accepting those rules about burden of proof. Another reply appeals to coherence or reflective equilibrium. Rules about burden of proof might be justified by having attractive implications for burdens of proof in particular cases. The best fit between rules and cases across a wide range of beliefs could then be used to determine which rules about burden of proof are justified without relying on any particular assumptions that need to be justified independently of the coherent set.Footnote ¹⁹ If these and other responses do not work, then the regress problem might show that there is no justified way to assign burden of proof or to determine what to believe in philosophy. Whether the regress problem has such radical implications depends on whether there is any way to select and justify rules about burden of proof in philosophy.

Unfortunately, philosophers rarely discuss burden of proof. They merely assume it implicitly without openly endorsing or arguing for any theory or rules about burden of proof. This omission might explain why classic philosophical disagreements persist so long and never get fully resolved.

Maybe Schauer can help. However, it is not clear how to apply Schauer’s pragmatic approach to philosophy, because it is often unclear which consequences follow from adopting or rejecting a philosophical stance. Unlike courts, philosophers do not reach verdicts in the sense of authoritative decisions that affect the welfare of specific parties. Indeed, as I said, making a claim in philosophy sometimes amounts to no more than accepting it for oneself without telling anyone else, so the burden of proof in philosophy is supposed to apply not only to public statements but also to private beliefs. The effects of such mental states are hard to estimate. That is part of why it is so difficult to settle the issue of who has the burden of proof regarding a philosophical claim.

To try to fill this gap in philosophical methodology, let’s consider a variety of proposals for rules governing burden of proof in philosophy. Each rule might seem plausible initially, but none will survive closer inspection.

IV. Formal Rules

One simple rule is that

1. (I) (a) Anyone who makes a positive claim has the burden of proving their claim, but (b) those who make a negative claim do not have this burden of proof.

If positive claims are assertions, and negative claims are denials, rule (I) basically says that assertions do and denials do not have the burden of proof.Footnote ²⁰

Applying this rule to philosophy, theists who make the positive claim that a case of Tay-Sachs is necessary for some adequately compensating good have the burden of proof, so they must show that Tay-Sachs is necessary for an effect that is good enough to compensate for the evil of Tay-Sachs. In contrast, Atheists make the negative claim that Tay-Sachs is not necessary for any compensating good, so this rule does not give them any burden of proving their claim. Atheists like this rule.

Of course, Theists will reply that rule (I) cheats and begs the question. Why should only positive claims have the burden of proof? One rationale might be that it is notoriously hard to prove a negative, and we often place the burden on the side that is easier to prove, such as when law puts the burden on showing that a defendant was coerced or entrapped, because it is too hard to prove that the defendant was not coerced or entrapped. However, it is easy to prove that not all acts or wills are free simply by showing that one act or choice was forced. Thus, the ease-of-argument rationale for rule (I) does not apply to all negative claims in philosophy.

Another problem with rule (I) is that it is often not clear which claim is positive, because this classification depends on which terms are used.Footnote ²¹ It seems negative to say that Tay-Sachs is not necessary for any compensating good, but it seems positive to say that it is possible to have some supposedly compensating good without Tay-Sachs. Yet these claims are equivalent. Again, to say that an act is free seems positive, but to say that an act is not caused or constrained seems negative. Yet these claims also seem equivalent. It is not clear how to apply rule (I) to claims for which the distinction between positive and negative is not well-defined.

A different formal rule instead says:

1. (II) (a) Anyone who makes a universal claim has the burden of proving their claim, but (b) those who make an existential claim do not have this burden of proof.

Universal claims include both “All dingos are dogs” and “No dingos are dogs,” because the latter means “All dingos are not dogs.” In contrast, “Not all dingos are dogs” is an existential claim, because it means (in non-Boolean logics) “Some dingos are not dogs.”

According to this rule, Physicalists who claim that all mental states, events, and properties are reducible to something physical need to carry a burden of proof, because their claim has a universal quantifier with wide scope. In contrast, Dualists who claim that some mental states, events, and properties are not reducible to anything physical do not have to carry the burden of proof, because their claim is not universal. Its form instead has an existential quantifier with wide scope. Dualists like this rule.

Of course, Physicalists can reject rule (II), so Dualists need to provide some reason for it. One rationale might be that a universal claim with “all” claims more than an existential claim with “some.” The universal claim is broader in the sense that it is about more things (indeed, everything), whereas the existential claim is about fewer things (only the subset that makes it true).Footnote ²² It might seem to make some sense intuitively to put the burden of proof on the person who claims more.

However, Physicalists can reply that it is harder to prove a universal claim, since that requires checking everything. It is easier to prove an existential claim insofar as it requires only a single counterexample. As with affirmative defenses mentioned above, we often place the burden of proof on the side whose claim is easier to prove. Moreover, if we check very many instances of an apparently universal rule, such as that all live humans have heads, then anyone who claims that some live humans do not have heads has the burden of proving their existential claim. Show me one! Analogously, physicalists claim that everything else that we have observed in the external world is physical, so anyone who claims that some mental state, event, or property is not physical has the burden of proving their existential claim by producing a counterexample. For this philosophical issue and others, then, rule (II) is at least not obvious.

Another possibility is to give up on separating formal kinds of claims and hold that:

1. (III) (a) Anyone who makes any claim has the burden of proving their claim, but (b) those who make no claim do not have this burden of proof.

Since making a claim in philosophy includes believing it, rule (III) is close to W. K. Clifford’s famous principle: “It is wrong always, everywhere, and for anyone to believe anything on insufficient evidence.”Footnote ²³

According to rule (III), both sides have the burden of proof regarding every philosophical issue. Theists and atheists, dualists and physicalists, hard determinists and defenders of free will, consequentialists and deontologists, moral realists and expressivists, and even dogmatic skeptics and commonsense philosophers all have the burden of proof.

Because it applies to all claims, rule (III) leaves only one way to escape the burden of proof: make no claim at all. This move was famously made by Pyrrhonian skeptics. Whereas Academic or Dogmatic skeptics claimed that nobody knows anything, Pyrrhonian skeptics claimed neither that nobody knows anything nor its negation that somebody knows something. Instead of making either claim, they suspend belief, even about Pyrrhonism itself.Footnote ²⁴

Pyrrhonism is attractive insofar as it avoids any burden of proof. Advocates of commonsense might claim that a Pyrrhonian who does not believe or endorse an obvious truth has the burden of showing what is questionable about that obvious truth. However, Pyrrhonians can reply that the burden of showing that a claim is questionable arises only for those who deny the claim or assert something contrary. Pyrrhonians do neither. They even grant that the commonsense claim might be true (or not) for all they know. So maybe they do avoid any burden of proof.

These attractions of Pyrrhonism have not led to swarms of supporters, though its long history does include several prominent philosophers.Footnote ²⁵ One reason for its lack of popularity might be that suspension of belief means that Pyrrhonians do not make any claim, so Pyrrhonism seems useless to those who want answers. If neither side can carry the burden of proof, Pyrrhonism leaves no way to justify adopting any philosophical position as opposed to any other. It might lead to ataraxia or tranquility, as some ancient Pyrrhonians suggested,Footnote ²⁶ but it cannot resolve any philosophical issue. Thus, it avoids rather than solves the problem of burden of proof in philosophy, if that problem is to justify making one claim instead of another.

V. Subjective Rules

The preceding rules focused on the claims being made—whether they are positive or negative, universal or existential, and claims or suspensions of belief. A different way of allocating burden of proof focuses instead on the person who believes the claim and their relation to it.

One rule of this sort distributes the burden of proof according to subjective certainty or maximal confidence:

1. (IV) (a) Anyone who makes any claim of which they are not certain has the burden of proving that their claim is true, but (b) those who make a claim of which they are certain do not have this burden of proof.

Schauer suggests something like this rule when he writes, “Questions of religious faith aside, when we are certain of some feature of the world, we do not need evidence for it, although we might have had evidence for it.”Footnote ²⁷ The assumption might be that, if we are already maximally confident, then evidence cannot make us more confident, so we do not need it.

Rule (IV) does not refer to objective certainty in the sense of there being no chance of error. Instead, rule (IV) refers to subjective certainty in the sense that I am as confident as I could be. To see the difference, imagine that I multiply 123 × 45 in my head and get 5535. I am not subjectively certain, because I know that I often make mistakes in mental calculations. Still, the claim that 123 × 45 = 5535 is objectively certain, because this time I got it right. In this case, rule (IV) says that I have the burden of proving that 123 × 45 = 5535. In contrast, if you are subjectively certain that 2 × 3 = 6, it seems more reasonable to think that someone who denies that 2 × 3 = 6 has the burden of proof, and you do not.

In contrast with arithmetic, we never have objective certainty in law. We sometimes have tons of evidence—reliable witnesses, fingerprints, uncoerced confession, motive, and opportunity—to show a defendant’s guilt. Then this verdict might be beyond a reasonable doubt. However, it is still not objectively certain, since it is possible that all this evidence separately and together is misleading.

Nonetheless, some jurors and judges might be subjectively certain about their verdicts. Similarly, some philosophers might be subjectively certain about their philosophical theories. The problem is then that, even if they are subjectively certain, if they should not be subjectively certain, then they still seem to have the burden of providing adequate evidence or argument for their position. The fact that they happen to be unjustifiably overconfident cannot relieve them of this burden.

This problem can be avoided by modifying rule (IV) so that it refers to whether the believer should be (or is justified in being or has the right to be) subjectively certain:

1. (V) (a) Anyone who makes any claim of which they should not be certain has the burden of proving that their claim is true, but (b) those who make a claim of which they should be certain do not have this burden of proof.Footnote ²⁸

Rule (V) differs from (I)–(IV) in that (V) deploys openly normative language “should.”

Its normative language might make rule (V) defensible, but it also makes it useless for resolving philosophical issues. To apply rule (V) to any issue, we need to determine which view on the issue should be subjectively certain. How can we determine that? One way might be to show that what we are certain about—our position—is supported by compelling evidence. However, this response in effect admits that we do have the burden of proof after all.Footnote ²⁹

Another way to determine when subjective certainty is justified is to appeal to facts about whether reasonable peers disagree. On this approach, however, philosophers should never be subjectively certain about their philosophical theories. Even if their theories would be objectively certain if they were true (like arithmetic equations), they should know that others and they themselves often make mistakes when they adopt philosophical theories. The fact that other capable and careful philosophers endorse contrary views at least suggests that they might be wrong. Surveys of professional philosophers in 2020 found that 19% are theists, 32% deny physicalism, 11% deny free will, 31% are consequentialists, and 26% deny moral realism.Footnote ³⁰ The fact that these positions are in the minority does not show that they are false or unjustified, of course, for they might reflect inadequate reflection or professional hiring practices. Still, these numbers at least suggest that neither side should be subjectively certain,Footnote ³¹ so both sides seem to have some burden of proof according to rule (V). As a result, rule (V) cannot help to resolve any of these controversial issues. The only way to resolve an issue is to argue for one side, but that in effect admits that both sides have a burden of proof. As a result, neither side can support or defend itself by denying that it has any burden of proof.

The appeal to surveys suggests an interpersonal rule that refers to the public instead of philosophers and avoids the normative language in rule (V):

1. (VI) (a) Anyone who makes any claim that is contrary to public consensus has the burden of proving their claim, but (b) someone who makes a claim supported by public consensus does not have any burden of proof.Footnote ³²

Public consensus can be taken to be near universal agreement. Some claims are neither contrary to nor supported by public consensus, because the public disagrees and does not reach any consensus. Rule (VI) does not say who has the burden of proof in those cases.

As a result, rule (VI) does not apply to many claims in philosophy. There is no public consensus about theism or atheism,Footnote ³³ dualism or physicalism, deontology or consequentialism, or moral realism or expressivism. Surveys do show that most people agree that some agents sometimes have some free will, but it is not clear what they mean by free will, so they might not endorse the same position as philosophers.Footnote ³⁴ Rule (VI) cannot help when it does not apply.

Nonetheless, rule (VI) does apply to some other philosophical issues. Almost everyone in the public agrees that somebody knows something, so dogmatic skepticism that denies this is contrary to public consensus, and its denial is supported by public consensus. Rule (VI) then implies that dogmatic skeptics have the burden of proof.Footnote ³⁵

Of course, that consensus alone is not enough to refute skepticism. Dogmatic skeptics reply that it begs the question to assume public consensus or use it to shift the burden of proof onto them, because public consensus is precisely what they deny. Moreover, if the public consensus is mistaken or unjustified, then the public should not agree that dogmatic skepticism is false. The question that settles who has the burden of proof is not the factual question of whether the public does agree but, instead, the normative question of whether the public should agree. That question cannot be settled by surveys alone without arguments, and the need for arguments is effectively a burden of proof.

Appeals to public consensus might have more force in law. Straying too far from common sense can lead the public to lose respect for the law and to refuse to obey it. It also makes it harder for people to predict what they need to do to avoid legal sanctions.Footnote ³⁶ In contrast, philosophers often value novelty and question public consensus and common sense. If they view themselves as gadflies, like Socrates,Footnote ³⁷ then it becomes a badge of honor that their claims are contrary to public consensus. This rebellious spirit does not show that they are correct or that they have no burden of proof, but it does motivate them to assign a burden of proof to what the public assumes, contrary to rule (VI).

VI. Pragmatic Rules

Rules (I)–(III) refer to the claim itself and (IV)–(VI) refer to people’s relations to the claim. None of these rules refers to future effects of distributing burden of proof in one way rather than another. This consequentialist or pragmatic approach is endorsed by Schauer, “setting the burden of proof, even if not done explicitly or deliberately, will unavoidably be based on an assessment of the purpose of the decision, the deeper values implicated, and the consequences that flow from mistakes.”Footnote ³⁸ I agree, but we need to distinguish several ways to build this insight into an explicit rule.

One could model the burden of proof on act consequentialismFootnote ³⁹:

1. (VII) (a) Someone who makes a claim has the burden of proof if making that claim has worse consequences than not making it on that particular occasion, but (b) they do not have the burden of proof if not making that claim has worse consequences than making it on that particular occasion. Footnote ⁴⁰

Recall that both privately believing the claim and publicly asserting it count as making that claim in philosophy. These two ways of making a claim can have different consequences, but the difference will not matter here.

One problem with (VII) concerns irrelevant consequences. If I am thinking about whether to endorse dualism or physicalism, and my best friend is a dualist who hates physicalists, then it might have worse consequences for me to put the burden of proof on dualism, because then I will become a physicalist, and my friend will hate me. Of course, the opposite holds if my best friend is a physicalist who despises dualists, since then I might lose my friend if I put the burden of proof on physicalism. The problem is that which side has the burden of proof in philosophy should not depend on whom I happen to be friends with at the time.Footnote ⁴¹ The same point holds if my community would reject me if I ended up holding a certain view.

To avoid such issues, we should not focus on particular cases. Instead, we need rules that are general in the sense that they apply to a wide range of cases that differ in the irrelevant consequences that create problems for (VII).Footnote ⁴² A better alternative is then analogous to rule consequentialismFootnote ⁴³:

1. (VIII) (a) Someone who makes a claim has the burden of proof if adopting a general rule that puts the burden of proof on claims like theirs will have better consequences than adopting a general rule that does not put the burden of proof on claims like theirs; but (b) they do not have the burden of proof if adopting a general rule that puts the burden of proof on claims like theirs will have worse consequences than adopting a general rule that does not put the burden of proof on claims like theirs.

To apply (VIII), we need to compare the harms caused by adopting the alternative general rules.

In criminal law, (VIII) implies that the prosecution has and should have the burden of proof if it would be better for the prosecution generally to have the burden of proof (with some exceptions). It would seem better to adopt that general rule if, as Blackstone quipped, “it is better that ten guilty persons escape, than that one innocent person suffer.”Footnote ⁴⁴ But was Blackstone right? Letting a guilty rapist go free can enable them to rape many innocent victims before they get caught again, so innocent people might be protected better by a looser burden of proof. Letting the guilty go free can also reduce respect for courts. So, why is punishing innocent people worse than letting guilty people escape? One answer is that causing harm is worse than allowing harm. Punishment directly causes harm to the person who is punished, whereas failing to punish the guilty merely allows and does not cause any crimes. Courts do not actively commit the crimes done by the guilty whom they release. This difference between doing and allowing harm might partly explain why the prosecution should have the burden of proof in legal trials.

Even if plausible in law, it is hard to apply (VIII) to philosophy. Neither side in philosophy is analogous to the prosecution in a court, because philosophical positions almost never directly cause harm to their opponents. We do not literally punish our philosophical rivals. Hence, the rationale for burden of proof in law cannot directly guide burden of proof in philosophy.

Other problems for applying (VIII) in philosophy arise from the vague phrase “claims like theirs.” This phrase is needed for (VIII) to be about general rules instead of particular claims or occasions. But when is a claim “like theirs”? This classification can be based on content, form, or belief. Consider each in turn.

If (VIII) focuses on content, it says, “Someone who makes a claim has the burden of proof if adopting a general rule that puts the burden of proof on any claim with a similar content will have better consequences than adopting a general rule that does not put the burden of proof on claims with a similar content ….” Even if this seems plausible, it is hard to apply this version of (VIII) without begging the question. To see why, consider a sample of the issues mentioned above:

1. (1) Theists might claim that a general rule that puts the burden of proof on them would tend to lead to atheism, which leads to hell. Of course, this burden is harmful only if theism is true. If there is no God, atheism does not lead to hell. Conversely, atheists might claim that a general rule that puts the burden of proof on them would tend to lead to theism, which causes great harms by fueling religious wars.Footnote ⁴⁵ However, theists can reply that these wars and harms are justified if they really are commanded by God.

2. (2) Proponents of free will might claim that a general rule that puts the burden of proof on them would tend to lead to skepticism about free will, which undermines valuable reactive attitudes and responsibility judgments.Footnote ⁴⁶ However, these attitudes and judgments are not justified unless we really do have free will. On the other side, deniers of free will might claim that a general rule that puts the burden of proof on them would tend to lead to believing and asserting free will, which leads to excessive and useless punishment.Footnote ⁴⁷ However, this punishment is not useless if the perpetrators deserve punishment, because they have free will.

3. (3) Deontologists might claim that a general rule that puts the burden of proof on them would tend to lead to consequentialism, which leads to violations of moral rights. However, this claim is correct only if people really do have the rights that deontologists claim. In response, consequentialists might claim that a general rule that puts the burden of proof on them would tend to lead to deontology, which leads to useless and counterproductive policies.Footnote ⁴⁸ But these policies are not useless if they protect real deontological rights.

Thus, each side on these issues can argue that, if they are correct, putting the burden of proof on them is harmful. But the other side can reply that, if they are correct, putting the burden of proof on them is harmful.Footnote ⁴⁹ This ground for allocating the burden of proof then cannot be applied without begging the question of which side is correct.

It might seem possible to avoid begging the question by focusing on the form of a claim instead of its content. If (VIII) focuses on form, it says, “Someone who makes a claim has the burden of proof if adopting a general rule that puts the burden of proof on any claim with a similar form will have better consequences than adopting a general rule that does not put the burden of proof on claims with a similar form ….” But which form counts? Perhaps adopting a general rule that places the burden of proof on any positive or universal claim will have better consequences than not adopting that rule. However, these claims about which rules have worse consequences are far from obvious and will run into the same problems as (I)–(II) above. Similarly, some might claim that adopting a general rule that places the burden of proof on any claim whatsoever will have better consequences than not adopting that rule. W. K. Clifford thought so,Footnote ⁵⁰ but William James replied that sometimes we need to hold beliefs without evidence because doing so has little cost and potentially great benefits.Footnote ⁵¹ Then it can be harmful to place the burden of proof on those claims. Moreover, if every claim has the burden of proof, then this rule cannot be used to resolve any philosophical dispute by denying the burden of proof on either side. Recall the discussion of (III) above. Thus, we cannot revive (I)–(III) by claiming that rejecting them will be harmful.

Another possible focus is the beliefs of those who make the claim. If (VIII) focusses on belief, it says, “Someone who makes a claim has the burden of proof if adopting a general rule that puts the burden of proof on any claim that is believed as strongly will have better consequences than adopting a general rule that does not put the burden of proof on claims that are believed as strongly ….” This proposal, however, runs into the same problems as (IV) above. Even when a philosopher believes their position as strongly as possible, if they should not believe it so strongly (or with such confidence or certainty), they still seem to have the burden of proof. The fact that they believe it more strongly than is justified cannot relieve them of this burden.

This problem can be avoided by focusing instead on what should be believed. Then (VIII) says, “Someone who makes a claim has the burden of proof if adopting a general rule that puts the burden of proof on any claim that should be believed as strongly will have better consequences than adopting a general rule that does not put the burden of proof on claims that should be believed as strongly ….” This shift to normative language, however, leads to the same problems as (V) above. How can we determine which claim we should believe? The only way is to show that the claim is supported by evidence or argument. This move requires believers to carry a burden of proof after all.Footnote ⁵²

Yet another variation on (VIII) might restrict the relevant better or worse consequences to inconsistent, false, or unjustified beliefs. The idea is that a philosophical position has the burden of proof when philosophers would be more likely to achieve their intellectual goals (consistent, true, and justified beliefs) and avoid the opposite (inconsistent, false, and unjustified beliefs) if philosophers adopted general rules and methods that place the burden of proof on positions like this one.

The problem with this last proposal should be obvious. Each side on a philosophical issue will claim that the other side has the burden of proof because it leads to inconsistent, false, or unjustified beliefs. They will also claim that philosophers will be more likely to achieve consistent, true, and justified beliefs if the burden of proof is not placed on their favored views. However, these claims will not be true if the other side is correct. They cannot apply this version of (VIII) to any issue without begging the question.

For these reasons, pragmatic rules like (VII)–(VIII)—including the discussed variations on (VIII)—cannot be used to determine which side has the burden of proof on any classic philosophical issue. Most importantly, they cannot be used to argue that one side does not have any burden of proving that its intuitions and premises are justified without evidence. If philosophers want to escape the burden of proving their assumptions, they need to find some different rule.