mercredi 2 août 2017

"Negative" claims and burdens of proof

This is the continuation of a discussion in another thread, where it was off-topic.

One often hears that "positive" claims have the burden of proof and "negative" claims the benefit of the doubt. This is, frankly, a naive and confused view, as far as philosophers, logicians and experts in critical thinking are concerned, and for good reason, which I'd like to state here.

For a fuller account of why this view is misguided, see my earlier posthere.

First, there is an obvious misnomer here. The claim is really about existential claims ("positive") and universal claims ("negative"). A common argument is the following:
Universal claims cannot be proved, so we cannot insist that they are proved before being accepted. Hence, they get the benefit of the doubt.
This is seriously misguided for at least a couple reasons. First, consider the following claim:
There is no normal, full-grown, visible elephant in my kitchen at this moment.
This statement (a universal/negative claim) is easily as provable as its negation. To be sure, it cannot be proved as certain if we take seriously concerns about hallucinations, illusions, etc., but neither can the corresponding existential claim. Both claims are verifiable to precisely the same extent.

To be sure, we rarely are concerned with proof in any sense even approaching mathematical certainty. Rather, we are interested in evidence sufficient to make a claim reasonably probable, probable enough that we ought to assent to the claim. Obviously, we can certainly find inductive evidence in favor of either universal or existential claims.

Second, let's just have a think here. Suppose we honestly think that universal claims could not be proved. Why on earth would this warrant presuming them true? This is not a reasonable conclusion. There are many statements we know to be unprovable (due to incompleteness or the fact that its negation is provable in a consistent system, say) that we certainly don't assent to. The notion that we ought to believe that which we think is unverifiable is really hard for me to understand.

On the contrary, if one asserts X, then the burden is on him to give reasons to accept X, whether X is existential or universal. Whether I assert that there is or is not a teapot orbiting Saturn, it is up to me to defend my assertion. This is not difficult if I deny that a teapot is there. I would simply point out that teapots are artifacts made by man, that Saturn is extraordinarily far from humans according to our best information and that it would be a remarkable and unlikely waste of resources for a group of humans to put a teapot there. These are sufficient reasons to conclude the universal statement is most likely true: there is no such teapot.

Similar arguments could be used to show that the statement "There is a rock orbiting Saturn" is very likely true, even though we can't see it from here.

If no such arguments are available, then of course the prudent man (the skeptic, for goodness' sake!) withholds judgment.


via International Skeptics Forum

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