Tuesday, June 21, 2005

菅豊彦「道徳的実在論の擁護」

を読んだ。日本語の本を読んだのはなんか久しぶり。著者はマッキーやブラックバーンの反実在論(後者は厳密には準実在論であるが、一応反実在論でくくる)を科学主義だとして批判して、自然言語によって開かれる「理由の空間」にある道徳的価値も実在すると主張する。近代科学の世界観では「数学の言葉で書かれている」第一性質しか実在の身分を認められないが、その世界観は偏狭すぎるのであって、「厚い」価値概念(cruelといった、事実的内容とともに価値評価を示している語)に見られるように事実と価値を相互に独立に二分することはできない。

著者の議論は道徳的実在論を確立していくというpositiveな議論というよりも、反実在論への批判を通してなされているのだが、細かい論点を一つ一つ批判していくというよりも、プログラム全体に関わる批判をしているので、著者の議論に対してありそうな批判をあんまりケアしてくれていない。

たとえば、第6章ではフランクフルトに従って「自由な意志(に基づく)」行為をする人はたとえdeterminismが正しくても自分の行為に対して責任を持ちうると論じられている。ここでの例は部屋に閉じこめられた人が脱出しようと試みる場合。著者はその人物はdeterminismが正しいなら、選択の自由(意志の自由)はもっていないが、彼・彼女の行為は自由な意志に基づいていると論じる。


たとえば、部屋に閉じこめられた人物が、結果として成功しないとしても、脱出したいという欲求を自己の意志として行為を試みる場合、それは「自由な意志」から行為しているのであり[...]。

脱出しようという「自由な意志」が成立する場合、この「自由な意志」の内容とは逆の意志[...]はその時点の彼には開かれておらず、従って彼には「意志の自由」(選択の自由)は存在しないかもしれない[...]。(p.168-9)

したがって、著者によると彼には自分の行為の責任があり、選択の自由がなくても自分の行為の責任を負うことになる。

しかし、よくわからないのはほんとうに選択の自由抜きで責任を考えられるかということ。つまりたとえ、著者の考える「ある時点」においてはすでに選択がされているゆえに意志の自由は存在しないとしても、それはあくまで選択の結果であり、「その時点」以前の彼を考えれば、やはり選択の自由と責任はリンクしているという反論があるかもしれない。もし「その時点」以前にも彼に選択の自由がないのならば、彼は一つしかない自分の欲求に従うことを意志することになる。これが「責任」概念の前提となる二階の欲求なのだろうか。

これがうまくいっているかどうかは全然わからないが、少なくともすぐ思いつきそうな反論ではある。しかし著者は素通りなので読んでいてちょっとつらいものがある。

とはいえ、この本は結構マクダウェルに基づいているので、マクダウェルの議論を知りたい人には有用かもしれない。

Sunday, June 19, 2005

ウィトゲンシュタインが種問題を解決

していたという記事。family resemblanceで種問題は解けるっていうじゃなーい。でもクラスター概念は昔からいってる人がいるのでここで「ウィトゲンシュタインが種問題を解決」ともっともらしくいう意味はそんなにありませんから。残念!!

Wednesday, June 15, 2005

囚人のジレンマゲーム

http://www.miskatonic.org/pd.html

まあそんなに面白いものではないですが。

Thursday, June 09, 2005

お金を払ってセックスをするサル

長いですが、NYTは登録が必要なので全文を載せます(元はここ)(セックスの話は後ろから3段落目)。しかしこのネタあんまり話題になっていないようなのが不思議。格好の2ch向きのネタなのになかったし(もしかして「と」なのか?)。

Monkey Business
By STEPHEN J. DUBNER and STEVEN D. LEVITT


Keith Chen's Monkey Research

Adam Smith, the founder of classical economics, was certain that humankind's knack for monetary exchange belonged to humankind alone. ''Nobody ever saw a dog make a fair and deliberate exchange of one bone for another with another dog,'' he wrote. ''Nobody ever saw one animal by its gestures and natural cries signify to another, this is mine, that yours; I am willing to give this for that.'' But in a clean and spacious laboratory at Yale-New Haven Hospital, seven capuchin monkeys have been taught to use money, and a comparison of capuchin behavior and human behavior will either surprise you very much or not at all, depending on your view of humans.

The capuchin is a New World monkey, brown and cute, the size of a scrawny year-old human baby plus a long tail. ''The capuchin has a small brain, and it's pretty much focused on food and sex,'' says Keith Chen, a Yale economist who, along with Laurie Santos, a psychologist, is exploiting these natural desires -- well, the desire for food at least -- to teach the capuchins to buy grapes, apples and Jell-O. ''You should really think of a capuchin as a bottomless stomach of want,'' Chen says. ''You can feed them marshmallows all day, they'll throw up and then come back for more.''

When most people think of economics, they probably conjure images of inflation charts or currency rates rather than monkeys and marshmallows. But economics is increasingly being recognized as a science whose statistical tools can be put to work on nearly any aspect of modern life. That's because economics is in essence the study of incentives, and how people -- perhaps even monkeys -- respond to those incentives. A quick scan of the current literature reveals that top economists are studying subjects like prostitution, rock 'n' roll, baseball cards and media bias.

Chen proudly calls himself a behavioral economist, a member of a growing subtribe whose research crosses over into psychology, neuroscience and evolutionary biology. He began his monkey work as a Harvard graduate student, in concert with Marc Hauser, a psychologist. The Harvard monkeys were cotton-top tamarins, and the experiments with them concerned altruism. Two monkeys faced each other in adjoining cages, each equipped with a lever that would release a marshmallow into the other monkey's cage. The only way for one monkey to get a marshmallow was for the other monkey to pull its lever. So pulling the lever was to some degree an act of altruism, or at least of strategic cooperation.

The tamarins were fairly cooperative but still showed a healthy amount of self-interest: over repeated encounters with fellow monkeys, the typical tamarin pulled the lever about 40 percent of the time. Then Hauser and Chen heightened the drama. They conditioned one tamarin to always pull the lever (thus creating an altruistic stooge) and another to never pull the lever (thus creating a selfish jerk). The stooge and the jerk were then sent to play the game with the other tamarins. The stooge blithely pulled her lever over and over, never failing to dump a marshmallow into the other monkey's cage. Initially, the other monkeys responded in kind, pulling their own levers 50 percent of the time. But once they figured out that their partner was a pushover (like a parent who buys her kid a toy on every outing whether the kid is a saint or a devil), their rate of reciprocation dropped to 30 percent -- lower than the original average rate. The selfish jerk, meanwhile, was punished even worse. Once her reputation was established, whenever she was led into the experimenting chamber, the other tamarins ''would just go nuts,'' Chen recalls. ''They'd throw their feces at the wall, walk into the corner and sit on their hands, kind of sulk.''


Chen is a hyperverbal, sharp-dressing 29-year-old with spiky hair. The son of Chinese immigrants, he had an itinerant upbringing in the rural Midwest. As a Stanford undergraduate, he was a de facto Marxist before being seduced, quite accidentally, by economics. He may be the only economist conducting monkey experiments, which puts him at slight odds with his psychologist collaborators (who are more interested in behavior itself than in the incentives that produce the behavior) as well as with certain economist colleagues. ''I love interest rates, and I'm willing to talk about their kind of stuff all the time,'' he says, speaking of his fellow economists. ''But I can tell that they're biting their tongues when I tell them what I'm working on.''

It is sometimes unclear, even to Chen himself, exactly what he is working on. When he and Santos, his psychologist collaborator, began to teach the Yale capuchins to use money, he had no pressing research theme. The essential idea was to give a monkey a dollar and see what it did with it. The currency Chen settled on was a silver disc, one inch in diameter, with a hole in the middle -- ''kind of like Chinese money,'' he says. It took several months of rudimentary repetition to teach the monkeys that these tokens were valuable as a means of exchange for a treat and would be similarly valuable the next day. Having gained that understanding, a capuchin would then be presented with 12 tokens on a tray and have to decide how many to surrender for, say, Jell-O cubes versus grapes. This first step allowed each capuchin to reveal its preferences and to grasp the concept of budgeting.

Then Chen introduced price shocks and wealth shocks. If, for instance, the price of Jell-O fell (two cubes instead of one per token), would the capuchin buy more Jell-O and fewer grapes? The capuchins responded rationally to tests like this -- that is, they responded the way most readers of The Times would respond. In economist-speak, the capuchins adhered to the rules of utility maximization and price theory: when the price of something falls, people tend to buy more of it.

Chen next introduced a pair of gambling games and set out to determine which one the monkeys preferred. In the first game, the capuchin was given one grape and, dependent on a coin flip, either retained the original grape or won a bonus grape. In the second game, the capuchin started out owning the bonus grape and, once again dependent on a coin flip, either kept the two grapes or lost one. These two games are in fact the same gamble, with identical odds, but one is framed as a potential win and the other as a potential loss.

How did the capuchins react? They far preferred to take a gamble on the potential gain than the potential loss. This is not what an economics textbook would predict. The laws of economics state that these two gambles, because they represent such small stakes, should be treated equally.

So, does Chen's gambling experiment simply reveal the cognitive limitations of his small-brained subjects? Perhaps not. In similar experiments, it turns out that humans tend to make the same type of irrational decision at a nearly identical rate. Documenting this phenomenon, known as loss aversion, is what helped the psychologist Daniel Kahneman win a Nobel Prize in economics. The data generated by the capuchin monkeys, Chen says, ''make them statistically indistinguishable from most stock-market investors.''

ut do the capuchins actually understand money? Or is Chen simply exploiting their endless appetites to make them perform neat tricks?

Several facts suggest the former. During a recent capuchin experiment that used cucumbers as treats, a research assistant happened to slice the cucumber into discs instead of cubes, as was typical. One capuchin picked up a slice, started to eat it and then ran over to a researcher to see if he could ''buy'' something sweeter with it. To the capuchin, a round slice of cucumber bore enough resemblance to Chen's silver tokens to seem like another piece of currency.

Then there is the stealing. Santos has observed that the monkeys never deliberately save any money, but they do sometimes purloin a token or two during an experiment. All seven monkeys live in a communal main chamber of about 750 cubic feet. For experiments, one capuchin at a time is let into a smaller testing chamber next door. Once, a capuchin in the testing chamber picked up an entire tray of tokens, flung them into the main chamber and then scurried in after them -- a combination jailbreak and bank heist -- which led to a chaotic scene in which the human researchers had to rush into the main chamber and offer food bribes for the tokens, a reinforcement that in effect encouraged more stealing.

Something else happened during that chaotic scene, something that convinced Chen of the monkeys' true grasp of money. Perhaps the most distinguishing characteristic of money, after all, is its fungibility, the fact that it can be used to buy not just food but anything. During the chaos in the monkey cage, Chen saw something out of the corner of his eye that he would later try to play down but in his heart of hearts he knew to be true. What he witnessed was probably the first observed exchange of money for sex in the history of monkeykind. (Further proof that the monkeys truly understood money: the monkey who was paid for sex immediately traded the token in for a grape.)

This is a sensitive subject. The capuchin lab at Yale has been built and maintained to make the monkeys as comfortable as possible, and especially to allow them to carry on in a natural state. The introduction of money was tricky enough; it wouldn't reflect well on anyone involved if the money turned the lab into a brothel. To this end, Chen has taken steps to ensure that future monkey sex at Yale occurs as nature intended it.

But these facts remain: When taught to use money, a group of capuchin monkeys responded quite rationally to simple incentives; responded irrationally to risky gambles; failed to save; stole when they could; used money for food and, on occasion, sex. In other words, they behaved a good bit like the creature that most of Chen's more traditional colleagues study: Homo sapiens.

Monday, June 06, 2005

An introduction to contemporary metaethics

Blackburnのquasi-realismへの反論としてC.Wrightがあげるのは、以下のmoral modus ponens argument:

i) Murder is wrong.
ii) If murder is wrong, then getting little brother to murder is wrong.
iii) Therefore, getting little brother to murder is wrong.

で、i)ii)を認めるのにiii)を認めない人が、Blackburnではせいぜい倫理的な過ちを犯している(crash of attitudes)だけで論理的な過ちを犯しているわけではないことになってしまうということ(Miller 2003, 4.4.)。(ここがほんとうはよくわからないのだが)

それに対してMiller(2003, 4.6.)は次の4つの場合を考えて、それぞれの場合で何が最善の解釈かを考える。

1)moral modus ponensは間違えるが、non-moral modus ponensは間違えない。
2)前者後者ともに間違える。
3)前者は間違えないが、後者は間違える。
4)前者後者ともに間違えない。

それでMillerはそれぞれの場合で実際は論理的な過ちを犯している(というのが最善の解釈な)のに倫理的な過ちを犯しているだけ(が最善の解釈)になってしまわないことを示す(2)と4)ではcounterfactual situationsを考えてそこで1)か3)のどちらかが実現されるかを考える)。

これはthe frequentist interpretation of the Linda problemとかcheater-detectorの話とかSextusの犬のdisjucntive syllogismの話とか、野球の選手が飛球を捕球するときにベイズの定理に従っているとかいう話(つまりあるタイプのrepresentationのもので(のみ)より抽象的な定理や論理に従っているように見える行動)に関係するような気がするのだが、よくわからん。またMillerのやり方がこの手の話に応用できそうな気もするが、これもよくわからん。