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Two Brains Running

In 2002, Daniel Kahneman won the Nobel in economic science. What made this unusual is that Kahneman is a psychologist. Specifically, he is one-half of a pair of psychologists who, beginning in the early 1970s, set out to dismantle an entity long dear to economic theorists: that arch-rational decision maker known as Homo economicus. The other half of the dismantling duo, Amos Tversky, died in 1996 at the age of 59. Had Tversky lived, he would certainly have shared the Nobel with Kahneman, his longtime collaborator and dear friend.

丹尼尔·卡纳曼(Daniel Kahneman)于2002年获得诺贝尔经济学奖。有意思的是,卡纳曼是一位心理学家。具体说来,他的贡献就在于他与另一位心理学家阿莫斯·特维斯基(Amos Tversky(自二十世纪七十年代初开始,挑战、瓦解了经济学理论界长期抱持的一个概念:称作“经济人”(Homo economicus)的理性优先决策者。特维斯基于1996年逝世,享年59岁。如果他还活着,他肯定会与其长期的合作者和挚友卡纳曼共享诺贝尔奖。

Human irrationality is Kahneman’s great theme. There are essentially three phases to his career. In the first, he and Tversky did a series of ingenious experiments that revealed twenty or so “cognitive biases” — unconscious errors of reasoning that distort our judgment of the world. Typical of these is the “anchoring effect”: our tendency to be influenced by irrelevant numbers that we happen to be exposed to. (In one experiment, for instance, experienced German judges were inclined to give a shoplifter a longer sentence if they had just rolled a pair of dice loaded to give a high number.) In the second phase, Kahneman and Tversky showed that people making decisions under uncertain conditions do not behave in the way that economic models have traditionally assumed; they do not “maximize utility.” The two then developed an alternative account of decision making, one more faithful to human psychology, which they called “prospect theory.” (It was for this achievement that Kahneman was awarded the Nobel.) In the third phase of his career, mainly after the death of Tversky, Kahneman has delved into “hedonic psychology”: the science of happiness, its nature and its causes. His findings in this area have proved disquieting — and not just because one of the key experiments involved a deliberately prolonged colonoscopy.

“人类的非理性”是卡纳曼的主要研究对象。他的职业生涯基本上分为三个阶段。在第一阶段,他和特维斯基做了一系列别出心裁的实验,揭示了二十多个“认知偏差”(cognitive biases)——推理中无意识的差错歪曲了我们对世界的判断。其中具有代表性的是“锚定效应”(anchoring effect):我们倾向于受正巧展露给我们的不相干数字的影响(例如,在一次实验中,经验丰富的德国法官如果掷出一对骰子后,刚好得到一个大数字,那么他们对商店扒手判的刑期就更长)。在第二阶段,卡纳曼和特维斯基证明,在不确定的情况下做决定的人,并非如传统经济学模型所假定的那样行事,他们并没有“效用最大化”(maximize utility)。两人随后发展出另一种更符合人类心理的解释决策的理论,他们称之为“预期理论”(prospect theory,卡纳曼便是因为这一成就获得诺贝尔奖)。在其职业生涯的第三个阶段——主要是在特维斯基过世以后——卡纳曼转向研究“享乐心理学”(hedonic psychology):快乐行为学及其性质和成因。他在这一领域的发现证明是令人不安的——这不仅仅是因为其中一个关键实验涉及一次故意延长的结肠镜检查。

“Thinking, Fast and Slow” spans all three of these phases. It is an astonishingly rich book: lucid, profound, full of intellectual surprises and self-help value. It is consistently entertaining and frequently touching, especially when Kahneman is recounting his collaboration with Tversky. (“The pleasure we found in working together made us exceptionally patient; it is much easier to strive for perfection when you are never bored.”) So impressive is its vision of flawed human reason that the New York Times columnist David Brooks recently declared that Kahneman and Tversky’s work “will be remembered hundreds of years from now,” and that it is “a crucial pivot point in the way we see ourselves.” They are, Brooks said, “like the Lewis and Clark of the mind.”

《思考,快与慢》(Thinking, Fast and Slow)的内容贯穿了以上这三个阶段。这本书内容丰富,它清晰、深刻,充满智慧的惊喜和自助价值。全书读来妙趣横生,在很多时候也很感人,尤其是卡纳曼讲述他和特维斯基共事的时候(“我们在一起工作获得的乐趣使我们变得格外地耐心;当你乐此不疲时,就不难做到精益求精。”)它对人类理性缺陷的洞见令人印象深刻,《纽约时报》专栏作家大卫·布鲁克斯(David Brooks)最近就宣称,卡纳曼和特维斯基的工作“将会流芳百世”,是“我们如何看待自己的关键支点”。布鲁克斯说,他们“就像思想界的‘路易斯与克拉克远征’ ”。


Now, this worries me a bit. A leitmotif of this book is overconfidence. All of us, and especially experts, are prone to an exaggerated sense of how well we understand the world — so Kahneman reminds us. Surely, he himself is alert to the perils of overconfidence. Despite all the cognitive biases, fallacies and illusions that he and Tversky (along with other researchers) purport to have discovered in the last few decades, he fights shy of the bold claim that humans are fundamentally irrational.


Or does he? “Most of us are healthy most of the time, and most of our judgments and actions are appropriate most of the time,” Kahneman writes in his introduction. Yet, just a few pages later, he observes that the work he did with Tversky “challenged” the idea, orthodox among social scientists in the 1970s, that “people are generally rational.” The two psychologists discovered “systematic errors in the thinking of normal people”: errors arising not from the corrupting effects of emotion, but built into our evolved cognitive machinery. Although Kahneman draws only modest policy implications (e.g., contracts should be stated in clearer language), others — perhaps overconfidently? — go much further. Brooks, for example, has argued that Kahneman and Tversky’s work illustrates “the limits of social policy”; in particular, the folly of government action to fight joblessness and turn the economy around.


Such sweeping conclusions, even if they are not endorsed by the author, make me frown. And frowning — as one learns on Page 152 of this book — activates the skeptic within us: what Kahneman calls “System 2.” Just putting on a frown, experiments show, works to reduce overconfidence; it causes us to be more analytical, more vigilant in our thinking; to question stories that we would otherwise unreflectively accept as true because they are facile and coherent. And that is why I frowningly gave this extraordinarily interesting book the most skeptical reading I could.


System 2, in Kahneman’s scheme, is our slow, deliberate, analytical and consciously effortful mode of reasoning about the world. System 1, by contrast, is our fast, automatic, intuitive and largely unconscious mode. It is System 1 that detects hostility in a voice and effortlessly completes the phrase “bread and. . . . ” It is System 2 that swings into action when we have to fill out a tax form or park a car in a narrow space. (As Kahneman and others have found, there is an easy way to tell how engaged a person’s System 2 is during a task: just look into his or her eyes and note how dilated the pupils are.)


More generally, System 1 uses association and metaphor to produce a quick and dirty draft of reality, which System 2 draws on to arrive at explicit beliefs and reasoned choices. System 1 proposes, System 2 disposes. So System 2 would seem to be the boss, right? In principle, yes. But System 2, in addition to being more deliberate and rational, is also lazy. And it tires easily. (The vogue term for this is “ego depletion.”) Too often, instead of slowing things down and analyzing them, System 2 is content to accept the easy but unreliable story about the world that System 1 feeds to it. “Although System 2 believes itself to be where the action is,” Kahneman writes, “the automatic System 1 is the hero of this book.” System 2 is especially quiescent, it seems, when your mood is a happy one.

更宽泛地说,第一系统运用联想和隐喻快速、粗糙地勾画出现实世界的草图,第二系统进而达到明确的信念和理性的选择。第一系统提出意图,第二系统执行。所以,第二系统似乎是老板,对吧?在原则上是的。但第二系统不仅仅更有意图、更加理性,同时也是懒惰的。它容易疲倦(流行的术语是“自我损耗”【ego depletion】)。与放慢节奏、对事物进行分析相反,第二系统常常满足于第一系统提供给它的简单却不可靠的关于这个世界的描述。“虽然第二系统相信自己乃行动之所在,”卡纳曼写道:“但自动的第一系统才是本书的主角。”当你心情愉快时,第二系统似乎尤其不活跃。

At this point, the skeptical reader might wonder how seriously to take all this talk of System 1 and System 2. Are they actually a pair of little agents in our head, each with its distinctive personality? Not really, says Kahneman. Rather, they are “useful fictions” — useful because they help explain the quirks of the human mind.



To see how, consider what Kahneman calls the “best-known and most controversial” of the experiments he and Tversky did together: “the Linda problem.” Participants in the experiment were told about an imaginary young woman named Linda, who is single, outspoken and very bright, and who, as a student, was deeply concerned with issues of discrimination and social justice. The participants were then asked which was more probable: (1) Linda is a bank teller. Or (2) Linda is a bank teller and is active in the feminist movement. The overwhelming response was that (2) was more probable; in other words, that given the background information furnished, “feminist bank teller” was more likely than “bank teller.” This is, of course, a blatant violation of the laws of probability. (Every feminist bank teller is a bank teller; adding a detail can only lower the probability.) Yet even among students in Stanford’s Graduate School of Business, who had extensive training in probability, 85 percent flunked the Linda problem. One student, informed that she had committed an elementary logical blunder, responded, “I thought you just asked for my opinion.”

要明白这一点,请想想“琳达问题”(the Linda problem)。卡纳曼认为这是他和特维斯基一起做的“最著名和最具争议性的”实验。实验的参与者会听到一个虚构的、名叫琳达的年轻女人的故事,她单身,坦率,非常开朗,在学生时代非常关注各种歧视和社会正义。接着,参与者会接受提问,以下哪一个更有可能:(1)琳达是一位银行出纳。(2)琳达是一位银行出纳,活跃于女权主义运动。大多数人都选择了(2)。换言之,提供的背景讯息表明“女权主义的银行出纳员”比“银行出纳员”更有可能。当然,这明显违背了概率法则(每一位女权主义的银行出纳都是银行出纳;补充的细节越多,可能性就越低)。然而,甚至在斯坦福商业研究院受过大量概率训练的学生当中,也有百分之八十五的人无法通过琳达问题。有一位学生在得知她犯了一个低级的逻辑错误后,答道:“我以为你只是在询问我的看法。”

What has gone wrong here? An easy question (how coherent is the narrative?) is substituted for a more difficult one (how probable is it?). And this, according to Kahneman, is the source of many of the biases that infect our thinking. System 1 jumps to an intuitive conclusion based on a “heuristic” — an easy but imperfect way of answering hard questions — and System 2 lazily endorses this heuristic answer without bothering to scrutinize whether it is logical.


Kahneman describes dozens of such experimentally demonstrated breakdowns in rationality — “base-rate neglect,” “availability cascade,” “the illusion of validity” and so on. The cumulative effect is to make the reader despair for human reason.

卡纳曼描述了许多这类经过实验证明的理性故障——“比率忽略”(base-rate neglect)、“有效性级联”(availability cascade)、“有效性的错觉”(the illusion of validity)等等。其结果就是逐渐让读者对人类的理性绝望。

Are we really so hopeless? Think again of the Linda problem. Even the great evolutionary biologist Stephen Jay Gould was troubled by it. As an expert in probability he knew the right answer, yet he wrote that “a little homunculus in my head continues to jump up and down, shouting at me — ‘But she can’t just be a bank teller; read the description.’ ” It was Gould’s System 1, Kahneman assures us, that kept shouting the wrong answer at him. But perhaps something more subtle is going on. Our everyday conversation takes place against a rich background of unstated expectations — what linguists call “implicatures.” Such implicatures can seep into psychological experiments. Given the expectations that facilitate our conversation, it may have been quite reasonable for the participants in the experiment to take “Linda is a bank clerk” to imply that she was not in addition a feminist. If so, their answers weren’t really fallacious.

我们真的如此无可救药吗?再想想琳达问题。甚至连伟大的生物进化学家斯蒂芬·杰伊·古尔德(Stephen Jay Gould)都受到它的困扰。作为一位概率专家,他知道正确的答案,但他写道,“有一个小人儿在我头脑里不断地跳上跳下,对我喊道——‘可她不仅仅是一个银行出纳;看一下描述吧。’”卡纳曼使我们相信,是古尔德的第一系统一直朝他喊着错误的答案。可是,也许发生着更为微妙的事情。我们的日常对话都发生在一个对期望未加说明的丰富背景下——语言学家称之为“言下之意”(implicatures)。这些言下之意可以渗透到心理实验中去。鉴于我们都期望让对话更加简洁,实验的参与者将“琳达是一位银行职”当作是在暗示“此外,她并不是一个女权主义者”,也是相当合理的。如果是这样,他们的答案就并非那么谬误。

This might seem a minor point. But it applies to several of the biases that Kahneman and Tversky, along with other investigators, purport to have discovered in formal experiments. In more natural settings — when we are detecting cheaters rather than solving logic puzzles; when we are reasoning about things rather than symbols; when we are assessing raw numbers rather than percentages — people are far less likely to make the same errors. So, at least, much subsequent research suggests. Maybe we are not so irrational after all.


Some cognitive biases, of course, are flagrantly exhibited even in the most natural of settings. Take what Kahneman calls the “planning fallacy”: our tendency to overestimate benefits and underestimate costs, and hence foolishly to take on risky projects. In 2002, Americans remodeling their kitchens, for example, expected the job to cost $18,658 on average, but they ended up paying $38,769.

当然,一些认知偏差甚至公然出现在最为自然的情景中。比如卡纳曼所说的“规划谬误”(planning fallacy):我们倾向于高估利润和低估成本,因而愚蠢地施行一些存在很大风险的方案。例如,在2002年,美国人改建厨房,预期这项工作平均花费18,658美元,但他们最后却花费了38,769美元。

The planning fallacy is “only one of the manifestations of a pervasive optimistic bias,” Kahneman writes, which “may well be the most significant of the cognitive biases.” Now, in one sense, a bias toward optimism is obviously bad, since it generates false beliefs — like the belief that we are in control, and not the playthings of luck. But without this “illusion of control,” would we even be able to get out of bed in the morning? Optimists are more psychologically resilient, have stronger immune systems, and live longer on average than their more reality-based counterparts. Moreover, as Kahneman notes, exaggerated optimism serves to protect both individuals and organizations from the paralyzing effects of another bias, “loss aversion”: our tendency to fear losses more than we value gains. It was exaggerated optimism that John Maynard Keynes had in mind when he talked of the “animal spirits” that drive capitalism.

规划谬误“只是一种普遍存在的乐观偏差的一个表现”,卡纳曼写道,这“很可能是最重大的认知偏差”。在某种意义上,一种倾向于乐观主义的偏差显然是糟糕的,因为它带来错误的信念——比如:是我们在掌控运气而不是运气在玩弄我们。但是,如果没有这一“掌控的错觉”,我们在早上甚至都没办法起床吧?比起与之相对应的更立足于现实的人,乐观主义者更具心理弹性,具备更强大的免疫系统,平均寿命更长。此外,正如卡纳曼所指出的,过分的乐观主义使个人和组织都免受另一种偏差的麻痹效应,这种偏差就是“损失规避”(loss aversion):我们对损失的畏惧更甚于对获利的重视。当约翰·梅纳尔德·凯恩斯(John Maynard Keynes)谈到驱策资本主义的“动物精神”(animal spirits)时,他头脑中就存在着过分的乐观主义。

Even if we could rid ourselves of the biases and illusions identified in this book — and Kahneman, citing his own lack of progress in overcoming them, doubts that we can — it is by no means clear that this would make our lives go better. And that raises a fundamental question: What is the point of rationality? We are, after all, Darwinian survivors. Our everyday reasoning abilities have evolved to cope efficiently with a complex and dynamic environment. They are thus likely to be adaptive in this environment, even if they can be tripped up in the psychologist’s somewhat artificial experiments. Where do the norms of rationality come from, if they are not an idealization of the way humans actually reason in their ordinary lives? As a species, we can no more be pervasively biased in our judgments than we can be pervasively ungrammatical in our use of language — or so critics of research like Kahneman and Tversky’s contend.



Kahneman never grapples philosophically with the nature of rationality. He does, however, supply a fascinating account of what might be taken to be its goal: happiness. What does it mean to be happy? When Kahneman first took up this question, in the mid 1990s, most happiness research relied on asking people how satisfied they were with their life on the whole. But such retrospective assessments depend on memory, which is notoriously unreliable. What if, instead, a person’s actual experience of pleasure or pain could be sampled from moment to moment, and then summed up over time? Kahneman calls this “experienced” well-being, as opposed to the “remembered” well-being that researchers had relied upon. And he found that these two measures of happiness diverge in surprising ways. What makes the “experiencing self” happy is not the same as what makes the “remembering self” happy. In particular, the remembering self does not care about duration — how long a pleasant or unpleasant experience lasts. Rather, it retrospectively rates an experience by the peak level of pain or pleasure in the course of the experience, and by the way the experience ends.

卡纳曼从未从哲学上抓住理性的特征。然而,他为能够作为其目标的幸福提供了一个迷人的描述。幸福是什么意思?当卡纳曼在1990年代中期首次提出这个问题时,大部分对幸福的研究还依赖于询问人们在大体上对他们的生活感到多么满意。但这种回顾性的评估依赖于记忆,众所周知,记忆是不可靠的。如果与此相反,一个人对快乐或者痛苦的实际体验能够随时随地取样,然后随着时间推移加以总结,那会怎样?卡纳曼将之称为“体验的”幸福,与研究者依赖的“记忆的”幸福相对立。他发现这两种对幸福的衡量方式存在惊人的差异。使“体验的自我”(experiencing self)感到幸福的东西并不是使“记忆的自我”(remembering self)感到幸福的东西。尤其是,记忆的自我并不在乎持续时间——不在乎一段愉快或者不愉快的经历持续多久。它会通过体验过程中痛苦或者快乐的峰值水平,通过体验的结果来回顾性地衡量一段体验。

These two quirks of remembered happiness — “duration neglect” and the “peak-end rule” — were strikingly illustrated in one of Kahneman’s more harrowing experiments. Two groups of patients were to undergo painful colonoscopies. The patients in Group A got the normal procedure. So did the patients in Group B, except — without their being told — a few extra minutes of mild discomfort were added after the end of the examination. Which group suffered more? Well, Group B endured all the pain that Group A did, and then some. But since the prolonging of Group B’s colonoscopies meant that the procedure ended less painfully, the patients in this group retrospectively minded it less. (In an earlier research paper though not in this book, Kahneman suggested that the extra discomfort Group B was subjected to in the experiment might be ethically justified if it increased their willingness to come back for a follow-up!)

记忆的幸福的两个缺陷——“对持续时间的忽略”(duration neglect)和“峰终定律”(peak-end rule)——在卡纳曼的一个更令人难受的实验中得到了惊人的展现。两组病人要接受痛苦的结肠镜检查。A组病人依照的是正常的程序。B组病人也一样,只不过——他们没被告知——在检查结束后,额外加上了几分钟的轻度不适。哪一组更痛苦呢?嗯,B组承受了A组的全部痛苦,然后还有额外的一些痛苦。但由于B组的结肠镜检查延长意味着结束时的痛苦要小于A组,这一组病人在回顾的时候就不那么在意(在更早的一篇研究论文中——虽然不在这本书里——卡纳曼提出,在这个实验中,如果B组受到的这阵额外的不适能够增强他们回来参加后续实验的意愿,它就是合乎伦理的!)。

As with colonoscopies, so too with life. It is the remembering self that calls the shots, not the experiencing self. Kahneman cites research showing, for example, that a college student’s decision whether or not to repeat a spring-break vacation is determined by the peak-end rule applied to the previous vacation, not by how fun (or miserable) it actually was moment by moment. The remembering self exercises a sort of “tyranny” over the voiceless experiencing self. “Odd as it may seem,” Kahneman writes, “I am my remembering self, and the experiencing self, who does my living, is like a stranger to me.”

在结肠镜检查中是如此,在生活中也是如此。在发号施令的是记忆的自我,而不是体验的自我。例如,卡纳曼引述研究表明,一个大学生决定是否重复一次春季假期,取决于前一个假期的峰终定律(peak-end rule),而不是取决于那一个一个瞬间多么有趣(或者多么悲惨)。记忆的自我对无声的体验的自我施加了一种“暴虐”。“好像很奇怪,”卡纳曼写道,“我是我记忆的自我,而那个过着我的生活的体验的自我,对我而言就像一个陌生人。”

Kahneman’s conclusion, radical as it sounds, may not go far enough. There may be no experiencing self at all. Brain-scanning experiments by Rafael Malach and his colleagues at the Weizmann Institute in Israel, for instance, have shown that when subjects are absorbed in an experience, like watching the “The Good, the Bad, and the Ugly,” the parts of the brain associated with self-consciousness are not merely quiet, they’re actually shut down (“inhibited”) by the rest of the brain. The self seems simply to disappear. Then who exactly is enjoying the film? And why should such egoless pleasures enter into the decision calculus of the remembering self?

卡纳曼的结论听起来很激进,也许还不够激进。也许根本就没有体验的自我。例如,以色列魏慈曼研究所(Weizmann Institute)的拉斐尔·马拉克(Rafael Malach)和同事进行的大脑扫描实验表明,当实验对象专注于一项体验,比如观看电影《黄金三镖客》(The Good, the Bad, and the Ugly),大脑中跟自我意识联系起来的部分不仅仅是安静了,实际上是被大脑的其他部分关闭(“抑制”)了。自我似乎消失了。那么,到底是谁在享受电影呢?为什么这种无我的快乐会进入记忆的自我的决策演算中呢?

Clearly, much remains to be done in hedonic psychology. But Kahneman’s conceptual innovations have laid the foundation for many of the empirical findings he reports in this book: that while French mothers spend less time with their children than American mothers, they enjoy it more; that headaches are hedonically harder on the poor; that women who live alone seem to enjoy the same level of well-being as women who live with a mate; and that a household income of about $75,000 in high-cost areas of the country is sufficient to maximize happiness. Policy makers interested in lowering the misery index of society will find much to ponder here.


By the time I got to the end of “Thinking, Fast and Slow,” my skeptical frown had long since given way to a grin of intellectual satisfaction. Appraising the book by the peak-end rule, I overconfidently urge everyone to buy and read it. But for those who are merely interested in Kahneman’s takeaway on the Malcolm Gladwell question it is this: If you’ve had 10,000 hours of training in a predictable, rapid-feedback environment — chess, firefighting, anesthesiology — then blink. In all other cases, think.

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