Theory on framework issues

Friday, February 11, 2011


Two distinct attitudes—which I'll call belief and opinion—go by the name “belief,” and distinct pathologies—fanaticism, opinionation, conformism, and equivocation— result from confusing them. The difference between belief and opinion is manner of formation. Beliefs are what you hold true, all things considered; opinions are what’s left after you factor out reliance on other people's beliefs. The way belief and opinion are confused differentiates the pathologies.

The distinction’s formal description might seem trivial, but its implications are counter-intuitive. A theorem that won economist Robert Aumann a Nobel Prize expresses the paradox. Aumann proved that if two agents in the same epistemic position have different beliefs, they should, rationally, split the difference.

To get the idea and see the point, start with simple factual beliefs. You and nine others estimate the number of marbles in a fish bowl. You observers are indistinguishable by your relevant abilities and experiences, but you guess higher than most others do. Then, Aumann's theorem (the "agreement theorem") says you should lower your estimate by adopting the average of all ten as your own belief. One way to explain the reason is each observer functions as a measuring instrument. If you have ten rulers with equal credentials for measuring length, you obtain the most reliable estimate by averaging the ten. You should treat each observer as a measuring instrument, and as you should average ten separate, epistemically indistinguishable rulers, you should adopt the average result of the human “instruments.” You have no rational basis to give more weight to your own opinion than to that of the other observers, even in forming your own belief.

This might be fine and well when applied to estimating marbles in a fish bowl, but think of applying the principle to important beliefs.

Next part: Is “epistemic equality” a fiction?

Correction (February 23, 2011): Aumann is best known for his agreement theorem (and for reactionary politics), but he won the Nobel Prize on other bases.


  1. Hey there. I've seen you over at Peter's blog and cl's blog. Can you further explain the distinction between belief and opinion? I really do not understand the following passage: "The difference between belief and opinion is manner of formation. Beliefs are what you hold true, all things considered; opinions are what’s left after you factor out reliance on other people's beliefs."

    So basically, beliefs are the result of our analysis and synthesis, but opinions are what we hold in spite of conflicting evidence, more popular beliefs, etc?

  2. Hi. Thanks for the question.

    We have two classes of information about a subject: our independent conclusions and things we believe because most people believe them. We _should_ base our beliefs partly on what other people think: if someone else is smarter and has thought harder about the subject, you _shouldn't_ think you're right and they're wrong. It's more likely you're wrong, and you should (to maximize your expected accuracy) give more weight to his conclusions than to yours.

    But under different circumstances, you should screen off other people's beliefs and consider only your independent analysis; a jury is an example one essay in this series uses. I think that situation arises frequently enough to give that kind of screened off cognitive attitude a name: opinion. [Good or bad choice?] How do you tell the difference between situations calling for one or the other, and what are the consequences of the difficulty people have grasping the distinction, at least in practical terms? That's what this series is about.

  3. Conceptually speaking, I think this distinction is necessary and helpful. This differentiation will, when fully understood by other, drive home the point that just because you came up with it yourself doesn't mean it's more valid. However, I find it hard to overcome my original definitions for opinion and belief. Not because they're more useful or even related, but because they're so ingrained into my thinking. Thank you for your explanation. I get it now.

    Unfortunately, I find that most people give more weight to their own conclusions than anyone else's due to their "right to an opinion" and arrogance. There are cases where isolated, independent analysis is more useful and can lead to better answers, but in the sciences and philosophy, I think the belief approach is best.


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SUPPLIER OF LEGAL THEORIES. Attorneys' ghostwriter of legal briefs and motion papers, serving all U.S. jurisdictions. Former Appellate/Law & Motion Attorney at large Los Angeles law firm; J.D. (University of Denver); American Jurisprudence Award in Contract Law; Ph.D. (Psychology); B.A. (The Johns Hopkins University). E-MAIL: Phone: 760.974.9279 Some other legal-brief writers research thoroughly and analyze penetratingly, but I bring another two merits. The first is succinctness. I spurn the unreadable verbosity and stupefying impertinence of ordinary briefs to perform feats of concision and uphold strict relevance to the issues. The second is high polish, achieved by allotting more time to each project than competitors afford. Succinct style and polished language — manifested in my legal-writing blog, Disputed Issues — reverse the common limitations besetting brief writers: lack of skill for concision and lack of time for perfection.