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July 18, 2011

The logic of science-6: The burden of proof in law

(For previous posts in this series, see here.)

For a long time, religion claimed to reveal eternal truths. No one except true believers seriously says that anymore because science has become the source of reliable knowledge while religion is increasingly seen as being based on evidence-free assertions. So some believers tend to try and devalue the insights science provides by elevating what we can call truth to only those statements that reach the level of mathematical proof, because such a high bar can rarely be attained and thus everything else becomes a matter of opinion. They can then claim that scientific statements and religious statements merely reflect the speaker's opinion, nothing more.

But science uses criteria other than proof for making judgments about truth. In making such judgments, scientists act more like judges in legal cases than mathematicians deriving proofs. For example, in legal proceedings, the usual practice is to follow the legal principle ei incumbit probatio qui dicit, non qui negat, which I am told (not knowing Latin myself) translates as "the burden of proof rests on who asserts, not on who denies", where the assertion is of a positive nature and not a negative one. So if someone is accused of committing a crime, the burden of proof is on the accuser and not the defendant. This principle is more popularly stated in English as that a person is presumed innocent until proven guilty beyond a reasonable doubt.

This principle is considered such a fundamental aspect of a civilized society that it is enshrined in Article 11 of the Universal Declaration of Human Rights which states that: "Everyone charged with a penal offence has the right to be presumed innocent until proved guilty according to law in a public trial at which they have had all the guarantees necessary for their defence." Of course many countries (including the US) routinely violate this principle when it suits them, while still smugly claiming to uphold the basic principles of human rights.

A point to note is that technically the only outcomes in a legal proceeding are "guilty" (i.e., proved beyond a reasonable doubt) and "not guilty" (not proved beyond a reasonable doubt). The defendant is never proven to be innocent, and has no obligation to do so. Indeed the defendant is not even obliged to provide any kind of defense at all. This can of course lead to undesirable situations where the jury can suspect that a defendant is indeed guilty of the crime but feels obliged to bring in a verdict of not guilty if the case has not met the 'proved beyond the reasonable doubt' standard which is why the 'proven innocent' phrasing is not appropriate for not guilty verdicts. But this kind of undesirable outcome is the price we pay for trying to have the fairest possible system, even if it should lead to public outcries of the sort seen following the not guilty verdicts in the O. J Simpson and Casey Anthony murder trials which were mistakenly interpreted by the public as statements that innocence had been proven when all it meant was that the presumption of innocence had not been contradicted.

One could have an alternative system in which a person is presumed guilty until proven innocent, shifting the entire burden of proof onto the defendant. There is nothing logically wrong with such system but in practice it would be unworkable since there are many more people who are innocent of a crime than there are those who are guilty. Furthermore it is often difficult, if not impossible, to prove innocence. For example, if I am asleep alone at home, it would be very difficult for me to prove that I was not robbing a nearby convenient store at that time, which is why the 'presumed innocent until proven guilty' standard seems to be a better one. So there are good reasons for having the burden of proof be on the person who asserts a positive claim and not on the person who denies as the method of arriving at legal verdicts or 'truths'.

Unless one agrees on which of the two frameworks (presumed innocent until proven guilty beyond a reasonable doubt or presumed guilty until proven innocent) to use in making legal judgments, it may be impossible to agree on a verdict. But whatever system one chooses, the basic structure is that there is a default position that is assumed to be true unless shown otherwise, so that proof of only one position is required.

Similar considerations apply in arriving at scientific truths.

Next: The burden of proof in science

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Comments

The framework of science is to presume that natural effects have natural causes. So, naturally (HA!), many people steeped in science are atheists and conclude natural effects have natural causes.

Shocking!

(Not to be interpreted as an argument in favor of theism - only that the choice is arbitrary)

Posted by healthphysicist on July 18, 2011 10:07 AM

Mano -

The better legal analogy, instead of the worn-to-death "proof beyond a reasonable doubt" standard in criminal law, is the lesser-known "preponderance of the evidence" standard of civil law. In a civil case, the burden of proof is still on the person asserting that something happened, but they only have to show that it is more likely than not that it happened, rather than beyond a reasonable doubt. This is why O.J. was found "not guilty" of the crime of murder, but was still civilly liable for wrongful death - evidence didn't exist beyond a reasonable doubt that he killed 2 people, but enough did exist to show that it was more likely than not that he did.

Science works the same way - an experiment doesn't have to prove a hypothesis beyond a reasonable doubt in order for it to be valid; the hypothesis simply has to fit the facts better than the null hypothesis (or any alternatives). I expect that you'll be touching on this tomorrow, so I wanted to offer a fuller look at the legal parallels.

Eric

Posted by Eric on July 18, 2011 10:19 AM

Eric,

Thanks for this. That is a good point which I will take into account.

Posted by Mano on July 18, 2011 11:52 AM

Not to be interpreted as an argument in favor of theism - only that the choice is arbitrary

No it isn't, because "supernatural" is not even a logically coherent concept. If x has observable effects on the natural world, it can be studied by the methods of science and it's a meaningless form of words to claim that x might be a "supernatural" phenomenon. If x in principle has no possible observable effects, it doesn't even make sense to say that x exists. Unless you try to reject the law of the excluded middle, those are the only two possibilities.

Posted by Steve LaBonne on July 18, 2011 02:38 PM

I didn't use the term "supernatural".

The Universe is the Universe.

If you label the Universe as natural and every observable thing within it as natural...everything will be natural. When you can't explain something, you'll say, "that's just the way it is" or "I don't know".

If you label the Universe as the product of an agent (braod theism), everything within it will be part of the product....everything will be the result of the act of an agent. When you can't explain something you'll say, "by God's grace".

The choice is arbitrary. Either you believe there's a god or not. The evidence either completely surrounds you (theist) or there has never been evidence (atheist).

Posted by healthphysicist on July 18, 2011 03:30 PM

The Universe is the Universe.

In which case there is room for Spinozism but none for theism.

No, believing in any old bullshit you want, even if completely incompatible with the scientific worldview, as theism decidedly is (just for starters, it's totally incompatible with both evolutionary biology and neurobiology), is not an option if you place any value on science and/or intellectual consistency.

Posted by Steve LaBonne on July 18, 2011 06:31 PM

You can believe any old bullshit you want whether you are an atheist or a theist. A theist (broadest sense, w/o splitting hairs on deism, polytheism, major religions, etc.) just believes the Universe is evidence of God.

What he/she does from there is up to him/her. If Spinozism is the result, it is. If not, it's not.

It has nothing to do with science or intellect.

(Note natural philosophy...to look for natural causes from natural effects...was coded in Newton's Principia. Newton, a scientific and mathematical genius, was a theist.)

Posted by healthphysicist on July 18, 2011 06:59 PM

of course, for a scientific study to be considered rigorous, a frequently used yardstick is p < 0.05, meaning that the pattern observed is less likely than 5% due be due to chance. This resembles the "beyond reasonable doubt" standard of criminal law.

Posted by Uri on July 23, 2011 04:33 PM

I agree completely with you contention that both parties are corrupt. As a famous statesmen once said when the public realizes they can vote themselves the treasury using corrupt public officials there goes democracy.

Posted by Michael Danno on July 25, 2011 08:13 AM