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Scientific Evidence, Legal Evidence, Rational Evidence

33 Post author: Eliezer_Yudkowsky 19 August 2007 05:36AM

Suppose that your good friend, the police commissioner, tells you in strictest confidence that the crime kingpin of your city is Wulky Wilkinsen.  As a rationalist, are you licensed to believe this statement?  Put it this way: if you go ahead and mess around with Wulky's teenage daughter, I'd call you foolhardy.  Since it is prudent to act as if Wulky has a substantially higher-than-default probability of being a crime boss, the police commissioner's statement must have been strong Bayesian evidence.

Our legal system will not imprison Wulky on the basis of the police commissioner's statement.  It is not admissible as legal evidence.  Maybe if you locked up every person accused of being a crime boss by a police commissioner, you'd initially catch a lot of crime bosses, plus some people that a police commissioner didn't like.  Power tends to corrupt: over time, you'd catch fewer and fewer real crime bosses (who would go to greater lengths to ensure anonymity) and more and more innocent victims (unrestrained power attracts corruption like honey attracts flies).

This does not mean that the police commissioner's statement is not rational evidence.  It still has a lopsided likelihood ratio, and you'd still be a fool to mess with Wulky's teenager daughter.  But on a social level, in pursuit of a social goal, we deliberately define "legal evidence" to include only particular kinds of evidence, such as the police commissioner's own observations on the night of April 4th.  All legal evidence should ideally be rational evidence, but not the other way around.  We impose special, strong, additional standards before we anoint rational evidence as "legal evidence".

As I write this sentence at 8:33pm, Pacific time, on August 18th 2007, I am wearing white socks.  As a rationalist, are you licensed to believe the previous statement?  Yes.  Could I testify to it in court?  Yes.  Is it a scientific statement?  No, because there is no experiment you can perform yourself to verify it.  Science is made up of generalizations which apply to many particular instances, so that you can run new real-world experiments which test the generalization, and thereby verify for yourself that the generalization is true, without having to trust anyone's authority.  Science is the publicly reproducible knowledge of humankind.

Like a court system, science as a social process is made up of fallible humans.  We want a protected pool of beliefs that are especially reliable.  And we want social rules that encourage the generation of such knowledge.  So we impose special, strong, additional standards before we canonize rational knowledge as "scientific knowledge", adding it to the protected belief pool.

Is a rationalist licensed to believe in the historical existence of Alexander the Great?  Yes.  We have a rough picture of ancient Greece, untrustworthy but better than maximum entropy.  But we are dependent on authorities such as Plutarch; we cannot discard Plutarch and verify everything for ourselves.  Historical knowledge is not scientific knowledge.

Is a rationalist licensed to believe that the Sun will rise on September 18th, 2007?  Yes - not with absolute certainty, but that's the way to bet.  (Pedants: interpret this as the Earth's rotation and orbit remaining roughly constant relative to the Sun.)  Is this statement, as I write this essay on August 18th 2007, a scientific belief?

It may seem perverse to deny the adjective "scientific" to statements like "The Sun will rise on September 18th, 2007."  If Science could not make predictions about future events - events which have not yet happened - then it would be useless; it could make no prediction in advance of experiment.  The prediction that the Sun will rise is, definitely, an extrapolation from scientific generalizations.  It is based upon models of the Solar System which you could test for yourself by experiment.

But imagine that you're constructing an experiment to verify prediction #27, in a new context, of an accepted theory Q.  You may not have any concrete reason to suspect the belief is wrong; you just want to test it in a new context.  It seems dangerous to say, before running the experiment, that there is a "scientific belief" about the result.  There is a "conventional prediction" or "theory Q's prediction".  But if you already know the "scientific belief" about the result, why bother to run the experiment? 

You begin to see, I hope, why I identify Science with generalizations, rather than the history of any one experiment.  A historical event happens once; generalizations apply over many events.  History is not reproducible; scientific generalizations are.

Is my definition of "scientific knowledge" true?  That is not a well-formed question.  The special standards we impose upon science are pragmatic choices.  Nowhere upon the stars or the mountains is it written that p<0.05 shall be the standard for scientific publication.  Many now argue that 0.05 is too weak, and that it would be useful to lower it to 0.01 or 0.001.

Perhaps future generations, acting on the theory that science is the public, reproducible knowledge of humankind, will only label as "scientific" papers published in an open-access journal.  If you charge for access to the knowledge, is it part of the knowledge of humankind?  Can we trust a result if people must pay to criticize it?  Is it really science?

The question "Is it really science?" is ill-formed.  Is a $20,000/year  closed-access journal really Bayesian evidence?  As with the police commissioner's private assurance that Wulky is the kingpin, I think we must answer "Yes."  But should the closed-access journal be further canonized as "science"?  Should we allow it into the special, protected belief pool?  For myself, I think science would be better served by the dictum that only open knowledge counts as the public, reproducible knowledge pool of humankind.

Comments (14)

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Comment author: Barkley_Rosser 19 August 2007 06:40:38PM 1 point [-]

Hmmm, well there is an endogeneity problem in that the believability of the police commissioner's statement depends on the degree to which it constitutes legal evidence. To the extent it constitutes legal evidence, it may be less believable precisely because this give police commissioners power that they may be exercising in corrupt and power-hungry ways. A statement that cannot be seen to potentially provide some personal gain to the person making it presumably has greater credibility.

Although it is almost always the case, I can imagine legal evidence that is not necessarily scientific. The problem in my mind is precisely this bad memory of witnesses problem. I guess we have to say that an eye witness account, under oath, is "scientific." It certain is legal evidence, although potentially challangeable by countervailing testimony or evidence. However, a scientist might be more willing to be skeptical, e.g. all those alien encounter accounts that are being discussed in other postings.

BTW, in regard to an earlier thread by Eliezer, of course "norm" does have various mathematical meanings, including the length of a vector (or multi-dimensional equivalent of "absolute value"), and there is the process of "renormalization" in algebra, which has some importance in several theories of physics. However, I remain unconvinced that any of these play an important role in establishing the earlier argument.

Comment author: Chris_Hibbert 19 August 2007 08:32:47PM 1 point [-]

I'm not sure the phrase "closed access" is a fair epithet to use against mainstream scientific journals. Even if they charge $20,000/year, most scientists have access to them via their institutional library, and there aren't many scientists who wouldn't send you a copy of their article if you asked for it. In many fields, the articles are available on the web after they appear in the journals. And if none of those apply to a particular article, you can probably visit a university library and read it there.

I'm not trying to deny that open access would be better, but it's not as if the scientific journals are trying to maintain a secretive cabal; they're doing a good job of spreading information among the involved professionals. The fact that there are more people interested these days means that open access would be more valuable than before.

It's still science, even if it's expensive to get access to the academy.

Comment author: Robin_Hanson2 19 August 2007 10:09:38PM 1 point [-]

The word "science" has a wide positive association, and it seems you want to be stingy with this word "science" and use its positive association to reward what you see as good behavior. But once people realize this is how you are trying to use the word, it may not have the effect you hope for.

Comment author: Robin_Hanson2 20 August 2007 01:33:06AM 0 points [-]

Would a paper describing data on a particular supernovae not be general enough to be science by your definition? Should those papers not have appeared in astronomy journals?

Comment author: Eliezer_Yudkowsky 20 August 2007 02:59:08AM 8 points [-]

Robin, I would say that the data on a particular supernova is "scientific evidence" because, as used, it's evidence you can use to form scientific generalizations about supernovae. The process of science does require doing particular experiments. But that such-and-such supernova was observed by such-and-such telescope to do this-and-whatnot is a historical truth, not a scientific truth - you can't verify it for yourself.

Indeed, the notion that "scientific evidence" is a deliberate social choice seems dangerous, and that's why it's important to pair it with the dictum that Bayesian evidence is objective and that all scientific evidence must be Bayesian evidence, i.e., it's not all up for grabs.

But, having said this, it seems to me that the cry "That isn't science!" has hurt more than it's helped, historically speaking, precisely because people do think there's an objective standard of science "out there" which their opponents are wilfully disobeying, as if science were Bayesian probability theory. So I think that it will indeed help to reframe the debate around the idea of "scientific standards" as an artificial social construct, used to achieve social ends, but still subject to the overriding mathematical constraints of Bayesian rationality.

It is better to have an explicit debate about social utility then to have a definition-fight framed as beliefs about what science really is. I am making a social-utility argument for openness as part of the rightful definition of science. I must expose this argument openly and let people criticize it, without charging them $30.

Comment author: Stuart_Armstrong 20 August 2007 03:58:55PM 1 point [-]

To the extent it constitutes legal evidence, it may be less believable precisely because this give police commissioners power that they may be exercising in corrupt and power-hungry ways.

You need to consider costs as well. The cost of a legal statment is much higher, in that the commissioner faces perjury charges if he utters a lie in court. But most importantly of all, is expected to back up his statement with solid evidence or a solid story of how he came to believe that X is a kingpin (both of which increase the chance of him being found out, if he is indeed lying).

Comment author: David_Gerard 14 February 2011 04:40:15PM 3 points [-]

For myself, I think science would be better served by the dictum that only open knowledge counts as the public, reproducible knowledge pool of humankind.

This is pretty much the next frontier for Wikimedia: make proper free content licenses the normal and expected thing.

(See, that's the power of a really good mission statement: everything you really want unpacks directly from it.)

Comment author: imd 05 January 2012 08:51:07AM -1 points [-]

All the kinds of knowledge you describe are subclasses of rational knowledge. Is there irrational knowledge?

Comment author: wedrifid 05 January 2012 09:03:47AM 0 points [-]

All the kinds of knowledge you describe are subclasses of rational knowledge. Is there irrational knowledge?

Believe stuff for crazy reasons (biased instincts, poor processing of data, etc). That's irrational knowledge - even if it happens to be wrong.

Comment author: imd 05 January 2012 10:19:52PM 1 point [-]

I was thinking more something like ethics.

Comment author: wedrifid 05 January 2012 11:13:23PM *  1 point [-]

I was thinking more something like ethics.

That could perhaps be called arational knowledge. The preference-like component of ethics, morals or desires which you have just because you have them.

Comment author: Vladimir_Nesov 05 January 2012 11:19:16PM *  0 points [-]

The preference-like component of ethics, morals or desires which you have just because you have them.

But is it something you wish to have, should have, should keep (in this particular form)? Nothing evades the judgment.

Comment author: wedrifid 05 January 2012 11:36:26PM *  0 points [-]

But is it something you wish to have

I personally do - but it isn't even an (absolute) human universal much less a logically necessary preference.

should have, should keep?

An agent could plausibly intrinsically value keeping all of their preferences/ethics/morals exactly as they are, in which case such an agent can be expected to believe that they should keep them. They may also instrumentally value keeping them if it helps them to achieve/live by/etc their preferences/ethics/etc. The moment they discover a better way to achieve preferences or live by ethics than by maintaining the representation in themselves the instrumental consideration no longer applies.

Nothing evades the judgment.

So? This doesn't impact imd's consideration at all. A rock that doesn't evade the judgement is still a rock and arational knowledge would not cease to be arational knowledge just because it does not evade judgement.

Comment author: FeatherlessBiped 08 January 2012 05:17:31AM 0 points [-]

According to classical philosophy (e.g. Aristotle), sense knowledge is knowledge, but knowledge of a kind which does not depend on a rational faculty. One could call that irrational, a-rational, non-rational, pre-rational, etc., depending on the how one has sliced up the phenomenology.