Burden of Proof

Andrew Russo

You say there’s no proof for God’s existence. Well, you can’t prove that God doesn’t exist!

A typical response from a theist

The burden of proof (BOP) fallacy is an informal fallacy involving the failure to recognize or properly assign the BOP in a persuasive reasoned dialogue, that is, an interchange between two or more parties whose aim is to prove or defend a position and, in doing so, persuade the other side of its truth or plausibility.

The BOP fallacy can occur in two ways. The first is when one side of the dia­logue fails to recognize that its opponent incurs the BOP. Walton (1988) presents the following hypothetical exchange between members of a legislature:

Billy: Why are my constituents the targets of such savage and unacceptable cutbacks?

Suzy: The government is doing the best it can to retrain employees and proceed in a humane manner. (235)

Billy’s question presupposes that the cutbacks are “savage and unacceptable,” and this may be a matter for further debate. Thus if Suzy had challenged this, it is Billy who incurs the burden of showing why the cutbacks are “savage and unacceptable.” However, since Suzy failed to recognize where the BOP lies in this instance, she conceded to Billy more than he deserved. As this case illus­trates, the failure to recognize where the BOP lies can amount to a failure to recognize one’s strongest argument.

The second way the BOP fallacy can occur is when one side of the dia­logue assigns the BOP incorrectly. Suppose that Jane is a skeptic and John an apologist of the paranormal:

Jane: The existence of entities such as ghosts should be given no credence whatsoever since there is no evidence that such things exist.

John: Your skepticism is unwarranted. Science has never disproven the existence of ghosts.

John’s reply assumes that it is Jane who incurs the BOP and that belief in ghosts is justified until some evidence against it is presented. But, in fact, the BOP lies with John. Although it is right that one cannot be certain that ghosts do not exist, it is John who has the burden of explaining why no one has ever been able to conduct a repeatable experiment with which to detect the existence of paranormal entities.

It is interesting to note that Jane’s argument is an argumentum ad igno­rantiam as her conclusion that no credence should be given to the existence of ghosts is based on the premise that there is no evidence for their existence (or, more abstractly, that not-P is true because there is a lack of evidence for P). Nevertheless, as Walton (1988) has argued, this form of argument is not necessarily fallacious so long as it is presented in a context where the BOP lies with the opponent to present positive evidence for her position. Thus, whether or not a particular argumentum ad ignorantiam is fallacious depends on “the requirements posed by the BOP” (238-239).

As another illustration of this, consider the dictum of American criminal law that the defendant is “innocent until proven guilty.” If the prosecution fails to present any evidence of guilt, the inference to a not guilty verdict is entirely legitimate. Additionally, if the prosecution were to claim that no evidence has been presented that disproves the defendant’s guilt, he or she would rightly be charged with incorrectly assigning the BOP to the defense. As Walton as well as Pigliucci and Boudry (2013) point out, our moral intuition that it is a greater injustice to convict an innocent person of a crime than allow a guilty person to go free explains why it is the prosecution that incurs the BOP in a criminal trial.

What determines which side of a dialogue incurs the BOP (if there is one)? Without a doubt, there is no simple answer to this question.

Burden of Proof 139

our moral intuitions that do the work. However, the example of Jane, the skeptic, and John, the sympathizer of the paranormal, presents a different scenario. What determines the BOP in this case is the present state of our background knowledge in addition to the prior probabilities of the claims under dispute. And, as Pigliucci and Boudry (2013) have argued, these pri­ors are best understood as set by the consensus of a community of experts.

There are still other factors that play a role in determining which side of a dialogue incurs the BOP. Suppose you are wondering whether to replace your home’s smoke detector. In a hypothetical debate about whether it is best to replace it or not, the BOP will typically lie on the side of not replac­ing it since the costs of having a broken smoke detector far outweigh the costs of replacing it (viz., endangering yourself and your family is far worse than the $15 you will spend to purchase a new smoke detector). In this sce­nario, it is the practical costs associated with each side of the debate that explain where the BOP lies and why there is a presumption in favor of replacing the device.

References

Pigliucci, Massimo, and Maarten Boudry. 2013. “Prove it! The Burden of Proof

Game in Science vs. Pseudoscience Disputes.” Philosophia (42): 487-502. Walton, Douglas. 1988. “BOP.” Argumentation (2): 233-254.