“Do not walk to the truth, but dance. On each and every step of that dance your foot comes down in exactly the right spot. Each piece of evidence shifts your beliefs by exactly the right amount, neither more nor less. What is exactly the right amount? To calculate this you must study probability theory. Even if you cannot do the math, knowing that the math exists tells you that the dance step is precise and has no room in it for your whims.” — from “Twelve Virtues of Rationality”, by Eliezer Yudkowsky

One of the more useful mental tools I’ve found is the language Lojban ( http://www.lojban.org/tiki/Learning ), which makes explicit many of the implicit assumptions in languages. (There’s also a sub-language based on Lojban, called Cniglic ( http://www.datapacrat.com/cniglic/ ), which can be added to most existing languages to offer some additional functionality.)

One of the things Lojban (and Cniglic) has are ‘evidentials’, words which can be used to tag other words and sentences to explain how the speaker knows them: “ja’o”, meaning “I conclude”, “za’a” meaning “I observe”, “pe’i” meaning “It’s my opinion”, and more. However, there hasn’t been any easy and explicit way to use this system to express Bayesian reasoning…

… until today.

Lojban not only allows for, but encourages, “experimental” words of certain sorts; and using that system, I have now created the word “bei’e” (pronounced BAY-heh), which allows a speaker to tag a word or sentence with how confident they are, in the Bayesian sense, of its truth. Taking an idea from the foundational text by E.T. Jaynes, “bei’e” is measured in decibels of logarithmic probability. This sounds complicated, but in many cases, is actually much easier to use than simple odds or probability; adding 10 decibels multiplies the odds by a factor of 10.

The current reftext for “bei’e” is at http://www.lojban.org/tiki/bei%27e , which basically amounts to adding Lojbannic digits to the front of the word:

ni’uci’ibei’e -oo 0% 1:oo complete disbelief, paradox
ni’upabei’e -1 44.3% 4:5
ni’ubei’e <0 <50% <1:1 less than even odds, less likely than so
nobei’e 0 50% 1:1 neither belief nor disbelief, agnosticism
ma’ubei’e >0 >50% >1:1 greater than even odds, more likely than not
pabei’e 1 55.7% 5:4 preponderance of the evidence
rebei’e 2 61.3% 3:2
cibei’e 3 66.6% 2:1 clear and convincing evidence
vobei’e 4 71.5% 5:2
mubei’e 5 76.0% 3:1 beyond a reasonable doubt
xabei’e 6 80.0% 4:1
zebei’e 7 83.3% 5:1
bibei’e 8 86.3% 6:1
sobei’e 9 88.8% 8:1
panobei’e 10 90.9% 10:1
pacibei’e 13 95.2% 20:1
xarebei’e 62 99.99994% 1,500,000:1 5 standard deviations
ci’ibei’e oo 100% oo:1 complete belief, tautology
xobei’e ? ?% ?:? question, asking listener their level of belief

By having this explicit mental tool, even if I don’t use it aloud, I’m finding it much easier to remember to gauge how confident I am in any given proposition. If anyone else finds use in this idea, so much the better; and if anyone can come up with an even better mental tool after seeing this one, that would be better still.

.uo .ua .uisai .oinairo’e

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