Tuesday, February 7, 2012

Inferring an "is" from an "ought"

You tell me that you saw a beautiful sunset last night. I conclude that you saw a beautiful sunset last night. You are talking about Mother Teresa. I conclude that you won't say that she was a sneaky politician. You promise to bake a pie for the party tomorrow. I conclude that you will bake a pie for the party tomorrow or you will have a good reason for not doing so. I tell a graduate student to read a page of Kant for next class. I conclude that she will read a page of Kant for next class or will have a good reason for not doing so.

All of these are inferences of an "is" from an "ought". You ought to refrain from telling me you saw a beautiful sunset last night, unless of course you did see one. You ought not say that Mother Teresa was a sneaky politician, as she was not. You ought not fail to bake the promised cake, unless you have good reason. The student ought not fail to read the Kant, unless she has good reason.

All of these are of a piece. We have prima facie reason to conclude from the fact that something ought to be so that it is so. In particular, belief on testimony is a special case of the is-from-ought inference.

In a fallen world, all of these inferences are highly defeasible. But defeasible or not, they carry weight. And there is a virtue—both moral and intellectual—that is exercised in giving these inferences their due weight. We might call this virtue (natural) faith or appropriate trust. We also use the term "charity" to cover many of the cases of the exercise of this virtue: To interpret others' actions in such ways as make them not be counterinstances to the is-from-ought inference is to charitably interpret them, and we have defeasible reason to do so.

The inference may generalize outside the sphere of human behavior. A sheep ought to have four legs. Sally is a sheep. So (defeasibly) Sally has four legs.

I used to think that testimony was epistemically irreducible. I am now inclined to think it is reducible to the is-from-ought inference. Seeing it as of a piece with other is-from-ought inferences is helpful in handling testimonial-like evidence that is not quite testimony. For instance, hints are not testimony strictly speaking, but an inference from a hint is relevantly like an inference from testimony. We can say that an inference from a hint is a case of an is-from-ought inference, but a weaker one because the "ought" in the case of a hint is ceteris paribus weaker than the "ought" in the case of assertion. Likewise, inference from an endorsement of a person to the person's worthiness of the endorsement is like inference from testimony, but endorsement of a person is not the same as testimony (I can testify that a person is wonderful without endorsing the person, and I can endorse a person without any further testimony). Again, inference from endorsement is a special case of is-from-ought: one ought not endorse those who are not worthy of endorsement.

If is-from-ought is a good form of inference, the contraposition may-from-is will also be a good form of inference. If someone is doing something, we have reason to think she is permitted to do it. Of course, there are many, many defeaters.

It is an interesting question whether the is-from-ought inference is at all plausible apart from a view like theism or Plato's Platonism on which the world is ultimately explanatorily governed by values. There may be an argument for theism (or Plato's Platonism!) here.


Heath White said...

Very interesting. Michael Thompson, in Life and Action, says some things very generally along the same lines, but you are much easier to understand than Thompson.

However, he would offer a somewhat different view (maybe). Consider “Sheep ought to have four legs” vs. “Sheep have four legs” taken as a generic, rather than as a universal quantification. Thompson thinks the latter is more fundamental than the former; we understand the “oughts” about sheep, for example, once we have formed a picture of the generic or ideal-type sheep. (As I recall the argument for this was a little thin.)

I suppose one could say the same thing about humans or rational beings. “Rational beings assert truths; they keep their promises; they obey authorities” etc. Then perhaps there is a fairly direct, though not deductive, inference from “Rational beings assert truths; you are a rational being making an assertion; so what you assert is true.” That is, one need not call this an ought-is inference, but maybe a generic-is inference.

This turns on the relative priority of “oughts” and generic descriptions of what Thompson calls “life forms,” and I don’t have a firm opinion. At any rate, I think you’ve contributed something to epistemology of testimony. It sure beats “irreducible.”

Alexander R Pruss said...

Basing things off the ideal seems to me to run into problems of non-ideal situations: The ideal person never apologizes. :-)

I guess we can say: The ideal person apologizes after doing wrong. But that sounds like: The square is round when it is a circle.

Mike L said...

"Basing things off the ideal seems to me to run into problems of non-ideal situations..."

That reminds me of a criticism Anscombe once made of how marriage is spoken of in Vatican II's Gaudium et spes. That document contains a number of statements of the form "Marriage is _________," where the blank is filled in by a description of something wonderful. Her response was: "And when marriage isn't _______? What then?" If we "base things off the ideal," that's a hard question to answer.

Luis G. Oliveira said...

Here's an argument endorsed by a face-value interpretation of your claims:

P1. S told me she saw a sunset last night
P2. S ought not lie about seeing sunsets.
P3. If P1 and P2, then I have a prima facie reason for believing that S saw a sunset last night.
C. Therefore, I have a prima facie reason for believing that S saw a sunset last night.

P3 seems to capture the is-from-ought inference form that you suggest. It seems false to me.

Here's an argument from the same P1 to the same C that does not rely on the seemingly false P3:

P1. S told me she saw a sunset last night
P2. I have reasons to believe that S rarely lies.
P3*. If P1 and P2, then I have a prima facie reason for believing that S saw a sunset last night.
C. Therefore, I have a prima facie reason for believing that S saw a sunset last night.

We can likewise account for all the other inferences that you mention: we can couple the first premise with more 'is'-claims describing our knowledge (or beliefs, or justified believes, etc.) about the person involved and derive the conclusion you suggest.

Why then accept the is-from-ought inference form in the first place? (Perhaps the obvious answer: P3 does not seem false and P3* does not seem better. But really?)

Alexander R Pruss said...

(Parenthetically, I am inclined to think we lose something when capture rules of inference in conditionals. There is an argument to that effect in the case of modus ponens in Sextus Empiricus and others: modus ponens is formulated as a conditional, you need modus ponens to apply modus ponens. Maybe modus ponens is special, though.)

I may have been implicitly assuming a reader sympathetic to the idea that one doesn't reduce testimonial evidence to evidence on the basis of an empirical premise like P2*. Without the position in this post being available, such a reader would likely be an irreductionist about testimonial evidence. Obviously, your sympathies like with reductionism about testimonial evidence. That's a big debate, and we probably won't settle it here.

But for what it's worth, here are some thoughts.

1. So much of our knowledge is based on testimony that I don't know that we often enough have sufficient evidence independent of a prior trust in testimony for knowing empirical premises like P2*. I suppose one might introduce P2* as a hypothesis to explain the agreement between other people's testimony in cases where they testify about the same thing. But one could also have the hypothesis that when people testify about stuff we can't check, they typically lie. :-) Maybe we can also get to P2* through something like the way we get to belief about other minds? Most of the things I say aren't lies, so probably most of the things others say aren't lies. I think these things do give some justification in believing in P2*, but I am dubious whether the evidence is sufficient for knowledge. Now maybe you can make a reliabilist move and say that knowledge of P2* isn't required, just its truth. I am sympathetic to that (I don't think knowledge of P2 is required for testimonial knowledge--for a rule of inference to yield knowledge one does not have to know what the rule is).

2. I am sympathetic to the idea that the moral ought in assertion is that one ought to refrain from asserting something other than the truth (i.e., falsehood or nonsense). This is obviously very controversial, but it simplifies my inference. Your inference actually requires not P2*, but the premise that you have reason to think the speaker rarely says things that aren't true, or rarely says things of this sort (maybe the class is: reports of visual perception of obvious phenomena) that aren't true. This makes it even harder to get the evidence in 1.

3. Notice the nice anti-sceptical effects of the is-from-ought inference.

4. I don't make a very sharp distinction between epistemic and non-epistemic reasons. A propensity to make the is-from-ought inference where appropriate seems to be have a significantly morally virtuous component: the virtue of appropriate trust is a central social virtue. I do not think this moral virtue is reducible to the virtue of believing on the basis of the best statistics about the honesty of others.