Wednesday, September 22, 2010

What is a burden of proof?

In comments, Vinny asks why burdens of proof are a big deal in the first place?

What do we really mean by a burden of proof? Vinny gets right to the crux of the biscuit:
"Burden of proof" assertions between atheists and theists often boil down to "I can offer no positive proof for my position, but I am going to declare myself the winner anyway since you cannot offer any for yours either."
He's descriptively correct, but I think he underestimates the power of this position. A burden of proof requires one party in a controversy to actively do something positive; if that party fails to do what's required, her opponent need do nothing to actually win.

Note that the quoted description is very different from Vinny's other characterization: a burden of proof "is sort of like the 'tie goes to the runner' rule we used as kids playing baseball." But in this situation, both parties have to do something active to succeed; there is no "default" if neither party actively performs the required task: the runner must actively run from home plate to first base, and the defense must actively move the ball to first base. Furthermore, given enough time, neither party will fail. If the runner stands still, he will eventually be put out. If the shortstop holds the ball, the runner will eventually be safe.

There are situations where it seems important to asymmetrically set one party a task she can fail to perform, and require a task from her opponent only if she succeeds. To carry on the baseball allegory*, the pitcher has an asymmetric task of throwing a strike: he can fail at that task (since he gets only one try), and if he does fail, the batter need not do anything to be safe. If the pitcher throws a strike, he has successfully transferred a metaphorical "burden of proof" to the batter: the batter must make contact with the ball: if he fails to do so, the defense need not do anything for the batter to be out.

*Using grossly oversimplified rules of baseball.

So why do we need the concept of "burden of proof" in argument? Are arguments more like the metaphorical symmetric situation, where the "burden of proof" is applicable only if both parties perform their active tasks exactly equally? Or are there some situations where we might say that one party has a requirement to actively fulfill some requirement, achieve some task; a good try doesn't count if the requirement is not actually fulfilled.

In criminal* cases, however, the prosecution has the initial burden of proof, a burden that's different from the "beyond a reasonable doubt" standard of proof she must eventually achieve. The prosecution must actively introduce some evidence establishing the elements of the crime. If she fails to do so, the defense can effectively rest without introducing additional evidence, and in closing remark only on the prosecutor's failure to meet her burden of introducing some evidence.

*As best I understand with my Law & Order J.D., which focuses on criminal procedure and law.

If, however, the prosecutor does introduce some evidence, the defense now has a burden to cast reasonable doubt on that evidence (or to raise an affirmative defense); if the defense fails to do so, a conviction will probably result* without further argument by the prosecution. What we see are shifting burdens of proof to achieve a standard of proof.

*Unless as in Twelve Angry Men the jury does the defense attorney's work for him.

The notion of "innocent until proven guilty" establishes neither a burden nor a standard of proof: it only specifies what happens if the standard is not met by the process of shifting burdens of proof.

Given this notion of what a burden of proof is, I'll talk about its applicability in philosophy in the next a future post.


  1. Just to clarify, the burden of proof works to decide in two types of situations:

    (1) There is evidence on the question but it is so closely balanced that it is impossible to say that the preponderance is on either side.

    (2) There is no evidence on either side of the question.

    The main point to the "tie goes to the runner" analogy is that the only available options are "safe" and "out" (although I guess we sometimes used "do over" playing whiffle ball in the back yard). You are correct that the analogy doesn't work nearly as well to the situation where there is no evidence.

    One thing that is not always made clear on Law and Order is the "burden of production." For certain affirmative defenses like self-defense, it is the defendant's burden to produce some evidence to put the issue in question. Once the defendant has met the burden of production, the prosecution must prove beyond a reasonable doubt that the defendant was not acting in self-defense.

  2. In the previous thread on burdens of proof, Dagood makes an interesting comment which seems relevant to this thread as well, and which I'm taking the liberty of reproducing in full. Because adding this preamble breaks the comment size limitation, I've split the comment in two pieces.

    I have noticed “Burden of Proof” can be utilized differently by various fields of study. I hesitated to comment about what it means in the legal profession, as we do not hold any copyright to the definition. A philosopher or scientist or lay person could mean something else, and I am in no position to dictate what it MUST be.

    And lawyers speak on the burden in terms people understand causing further possible confusion.

    In the legal field, the party making the claim has the Burden of Proof. Always. In a criminal matter, it is the prosecutor who has the burden to prove 1) a crime was committed and 2) by the defendant. (As you correctly point out, the Burden is not the same as the Standard of proof—i.e. “beyond a reasonable doubt” in a criminal matter.) In a civil monetary matter, it is the Plaintiff who has the burden to prove 1) the defendant is liable and 2) the plaintiff was damaged. [I hope the reader understands I am making this extremely simplistic.]

    A Burden rarely shifts, but only in specific situations; generally, it is safe to say it never shifts.

    For example, the prosecutor always has the burden, however—if the Defendant claims “alibi” then the Defendant has the burden of proving that defense—in that one instance, the burden on that sole issue has shifted. The Prosecutor is not charged with proving the Defendant does not have an alibi—i.e. does not have to prove a negative.

    Note, however, the Prosecutor still has the burden to prove the crime was committed and the Defendant committed the crime. The defense (and the same as “Affirmative Defenses”) never, ever have to be proven until the prosecutor [or plaintiff] has first proven their case.*

    *Of course there are always exceptions. For example, if there was a Statute of Limitations problem, because it is such a complete defense, and it would be infuriating to go through an entire trial only to throw out the case after all that work; Defendants bring that by motion prior to any proof. Most clients would not be happy to receive a $60,000 bill for a trial that could be avoided by a $1,000 motion.

  3. DagoodS continues...

    Because the prosecutor or plaintiff has the proof, the defendant would not have to present any evidence. Not make an opening statement, closing argument or even question a witness. And the prosecutor could still lose by not sustaining their Burden of proof. I often say, in opening statements in criminal matters to press this point, “The defendant and I could sit here and play cards, or read books throughout this trial. Never ask a question; never make a sound. And you can still find that the prosecutor has failed to present sufficient evidence to prove beyond a reasonable doubt that my client committed this crime. They must prove their case!”

    We do, though, as defense counsel, have the right to present relevant evidence—evidence that makes a fact that is of consequence to the action more probable or less probable than it would be without the evidence.

    So while the prosecutor is presenting her evidence, supporting facts toward the proposition of my client’s guilt, I present evidence to make those facts less probable. I do not have the technical legal burden to do so to prevail, but I do have a moral, ethical obligation to my client (not to mention a standard of care to avoid malpractice) to present such evidence.

    It can appear, as both sides tussle, the Burden is shifting back and forth, but it really isn’t. As a pragmatic matter, if you have a particularly damning piece of evidence, you are not going to withhold it simply because the other side has the burden.

    As you pointed out, if you can respond to an argument regarding intelligent design—do so! In a court case, you may not have to do so under the Burden, yet realistically you would anyway.

    Frankly, your point still sustains, and I didn’t respond initially because it nitpicks the minor, narrow legal use of the Burden, while what I took as your over-all position remains robust.


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