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What is the Burden of Proof?
The allocation of the burden of proof-- who has it and what weight it has-- has implications for what we have to do as logical and critical thinkers.
To have the burden of proof is to be rationally required to produce evidence for your assertion claims.
Burdens of proof come in degrees.
To have a heavier burden of proof than some opponent is to be rationally required to produce more or better evidence for your assertion claims than your opponent is rationally required to produce.
On that account, the allocation of the burden of proof– who has it and what weight it has– has implications for what we have to do as logical and critical thinkers.
If we have it, we have to do more, produce more reasons or stronger reasons perhaps. And if we don’t have it, it seems we can get away with doing less.
Here is a summary of Dare and Kingsbury ‘Putting the Burden of Proof in Its Place: When Are Differential Allocations Legitimate’ (2008) 26 Southern Journal of Philosophy 503-518.
- The Burden of Proof
The legal example: People accused of crimes are presumed innocent. The burden of proving that they are guilty rests on the prosecutor. The accused doesn’t have to prove anything. If the prosecutor doesn’t meet the burden, the presumption that the accused is innocent stands: Innocent until proven guilty.
- The Common View
“It is rare, outside legal and quasi-legal contexts, for the burden of proof on one side of an argument to be recognised formally. Yet, the implicit idea … is found in all reasoning. One person has a more demanding job of proving a point and, if they fail, then an alternative position remains the preferred one.” Matthew Allen, Smart Thinking 2004, p. 81
- The Common View and Our View
According to the common view: If the burden of proof (BOP) is on your opponent, you are entitled to sit back and wait for your claim to be disproved rather than having to provide positive arguments for it.
According to us: The common view is mistaken. It is only rarely OK to allocate the BOP unequally, or to say one position wins just because its opponents couldn’t meet the BOP. It’s almost always true that both sides to a dispute have an equal BOP, and so an equal responsibility to produce arguments for their views.
- In a bit more detail, we think that:
- Whether unequal allocations of the BOP are OK or not depends on the aim of the particular inquiry, and on whether or not an unequal allocation helps achieve that aim.
- Most generally, we distinguish between inquiries aimed at finding the truth and inquiries that are not.
- We think unequal allocations are most obviously OK when truth is not the primary aim.
- We think many defenders of the common view generalise from non-truth-directed practices because they think they’re the norm rather than the exception.
- Broad reasons to favour our view
- It fits better with the idea that good reasoners should always be able to provide reasons for their assertions.
- It fits better with the idea that argument is ‘truth-seeking’: concerned to lead us to hold true beliefs and reject false beliefs.
- It provides a response to the worry that sitting back and leaving your opponent to do all the work is an appeal to ignorance: in our view, in truth directed inquiries, you are almost never entitled to rely upon your opponent’s inability to show that their view is true.
- Non-Truth-Directed Practices
A Simple Case: Formal Debates
In formal debates (the ‘game’ in which two sides are given a topic, and follow a set of rules to see which side wins) each team has the burden of showing errors of fact or logic in the opposing team’s case. Unless the burden is met, their opponents’ claims stand.
“Rebuttal is vital. An argument, however weak, stands until it is rebutted …. Adjudicators cannot regard an argument as knocked down until the opposition has rebutted it effectively. If a team makes an error of fact or logic, the adjudicator cannot penalise them for it unless the other team points out the error…” (Auckland Debating Association Guidelines 2002).
Question: Why don’t unrebutted errors of fact or logic undercut an argument in a formal debate?
Answer: Because we’re not interested in truth in formal debate. We want rhetoric, entertainment, and to see teams noticing and responding to the flaws and strengths of the argument actually presented (as opposed to the best argument that could be presented).
A Trickier Case: The Law as a Non-Truth-Directed Practice
Remember the presumption of innocence: Accused people (‘defendants’) are entitled to offer no evidence at all. They are to be presumed innocent unless the prosecution can meet the burden of proving otherwise.
An example: Excluded Evidence: Police v Fowlie. Chris Fowlie, was President of the New Zealand National Organisation for the Reform of Marijuana Laws. He was charged after police found marijuana in his pocket. (It is illegal to possess marijuana in New Zealand).
The court found the search had been illegal:
“I conclude that even had the evidence been such as to prove beyond reasonable doubt all the requisite formalities … the search conducted of Mr Fowlie was unreasonable and the evidence obtained thereby should be regarded as inadmissible. The charge is dismissed”
Why exclude evidence which seems highly relevant to the question of Fowlie’s guilt? The answer (we think): Legal proceedings are concerned not just with finding out the truth about what happened, but with protecting important rights to liberty, against unlawful search, and the like. We care so much about those rights that we are prepared to sacrifice the search for truth in order to protect them. So, while law is not a game like formal debates, it too is not (solely or primarily) truth directed.
Other non truth-directed cases
Safety Cases: We put the burden wherever it is most likely to ensure that people are kept safe, even if it makes it harder to find out whether the activity really is safe.
- Truth-Directed Practices
In truth-directed practices, we claim, unequal allocations of the BOP are almost always illegitimate. In science, for instance, we say that a good scientist:
“… should be open to the possibility of evidence that conflicts with her view and should be prepared to respond to apparent conflicting evidence by investigating whether the evidence holds up under scrutiny and modifying the view if it does. Giving a scientific theory the status of a default position – assuming it to be true till the evidence for some competing view becomes overwhelming – seems to be one way of departing from this ideal. The default view is not held to the same standards of evidence as views that oppose it” (p.510).
A (bad) science example: H. pylori: In the early 1980s, it was accepted that stomach ulcers were caused by excessive gastric acid. In 1983, Barry Marshall and Robin Warren began reporting research linking gastritis and ulcers with a specific bacteria, Helicobacter pylori. Their work was summarily dismissed. In 1988, they performed a prospective, double blind trial comparing an antibiotic regimen with the standard ulcer therapy clearly demonstrating the role of H. pylori. However, it was not until 1994 that the National Institute of Health released a consensus statement accepting that antibiotics active against H. pylori should be the default ulcer therapy.
Now why is this a standard example of bad science?
“The “no acid, no ulcer” consensus was treated as a default position, to be abandoned reluctantly, and only in the face of overwhelming evidence. The mistake, we suggest, was essentially getting the allocation of the burden of proof wrong, placing too heavy a burden on the bacterial theory” (p511).
- A Problem for our View?
What about Legitimate Scientific Consensus? Do scientists respond to every challenge to scientific orthodoxy? If not, why not? We suggest that scientists don’t have to drop whatever they’re doing in the face of every challenge (e.g., claims that apricot pips cure cancer), because the ‘consensus view’ already has its evidence.
- Some Real Exceptions
Sometimes differential allocation helps us find the truth:
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The Caveat Emptor (Let the Buyer Beware) Case: Sellers may have better knowledge, but they may also have motive to hide the truth. Buyers may have to go through more trouble to find out the truth, but they have the best motive for doing so.
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The reversed burden in Income Tax Cases:
In many countries, taxpayers have the burden of proving the claim they make about taxable income or assets. Why?
“The key reason for the onus of proof being on taxpayers is that facts about the tax positions they take are primarily within their knowledge. Moreover, it is the taxpayer who exercises primary control over record-keeping, and over the extent to which there is full and honest disclosure to Inland Revenue.” (NZ IRD 2001)
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