I feel that it is time to share a secret. When I left on my holiday just over a week ago, I was fighting a battle with a deep-rooted addiction². I feel able to admit this, since over the course of my holiday I was able to go through cold turkey, conquer the addiction, and face the world clean.

从今以后，我只喝不含咖啡因的咖啡。上瘾——即使是像过滤咖啡这样温和的东西——是一个经济学家不太可能解决的问题，因为多数经济学理论的预测都是建立在理性行为基础上的，而上瘾似乎在本质上就是非理性的。

It’s decaffeinated coffee for me from now on. Addiction – even to something as benign³ as filter coffee - is an unlikely topic for an economist⁴ to tackle, because most economic theory is predicated on rational behaviour, and addiction seems to be quintessentially irrational⁵.

对该问题符合逻辑的回答出现在1988年。凯文?M?墨菲(Kevin M. Murphy)和诺贝尔经济学奖得主加里?贝克(Gary Becker)发表了《理性上瘾理论》(A Theory of Rational Addiction)一书，自此定义了经济学家研究上瘾的方法。该理论很容易阐述：瘾君子选择了自己的毒药，尽管他们知道容易上瘾，并且非常危险，他们这样做的原因是，他们期望上瘾带来的兴奋会超过它带来的痛苦。

The logical response appeared in 1988. A Theory of Rational Addiction was published by Kevin M. Murphy and Nobel laureate Gary Becker, and has defined economists⁶’ approaches to addiction ever since. The theory is easy to state: it is that addicts⁷ choose their poison despite knowing that it is habit-forming and dangerous, and they do so because they expect the highs to outweigh⁸ the lows.

即使其他经济学家对此也持怀疑态度。“他们不知道自己在说什么，”托马斯?谢林(Thomas Schelling)获得诺贝尔经济学奖不久后遇见我时说。谢林试图戒除烟瘾已经有多年时间了。

Even other economists are sceptical. “They don’t know what they’re talking about,” opined Thomas Schelling when I met him shortly after he, too, was awarded the Nobel prize in economics. Schelling had spent years trying to kick his tobacco addiction.

然而，理性上瘾方法可能并没有它看上去那样荒谬。一些习惯的养成是符合理性的。对我而言，跟女朋友约会已经足够形成习惯，以至最后向她求婚了。到目前为止，我并不后悔。

Yet perhaps the rational addiction approach is not quite as absurd as it seems. Some habits are rational to acquire. Dating my girlfriend was habit-forming enough for me to ask her to be my wife. So far I have no regrets.

将决定喝咖啡或开始约会与决定抽烟或注射海洛因相比，似乎颇为荒谬，但如果贝克和墨菲是对的，那么这种差别就不是性质上的，而是程度上的。 It seems absurd to compare the decision to drink coffee or start dating with the decision to smoke cigarettes or inject heroin⁹, but if Becker and Murphy are right the difference is not of kind, but of degree.

理性瘾君子应当具备某些行为特征。举例来说，他们不仅应当对当前的价格上涨做出反应，还应当对未来预期中的价格上涨做出反应。如果海洛因的价格可能上涨，那么理性的瘾君子就应当考虑在价格上涨之前戒掉毒瘾。

Rational addicts should behave in certain ways. They should, for instance, respond not just to current price increases but to expected future price hikes. If heroin is likely to get more expensive, rational addicts should consider trying to quit before that happens.

瘾君子对于持久的价格变化甚至可能比非瘾君子更加敏感。由于上瘾具有自我增强的特性，因此当理性瘾君子想戒瘾的时候，突然戒除法是做到这一点的高效率途径。

Addicts may even be more sensitive to lasting¹⁰ price-shifts than non-addicts. And since addiction is self-reinforcing, when the rational addict¹ wants to quit, cold turkey is the efficient way to do it.

经济学家已经找到了一些证据来支持这些论点：帕梅拉?莫比丽亚(Pamela Mobilia)发现，如果赌客预计赛马庄家的收入会增加（这将增加赌瘾的成本），他们就会减少赌注；尼尔斯?奥莱卡恩斯(Nilss Olekalns)和彼得?巴兹利(Peter Bardsley)发现，喝咖啡上瘾的人也表现出相似的先见之明；菲利浦?库克(Philip Cook)和乔治?陶亨(George Tauchen)发现，当美国一些县提高酒税时，肝硬化发病率比整体消费水平的下降幅度更大，表明减少饮酒量最多的是酗酒者。

Economists have found some evidence to support these ideas: Pamela Mobilia finds that betting at racetracks falls in anticipation¹¹ of increases in bookies’ takings, which would make the gambling¹² habit more costly¹³; Nilss Olekalns and Peter Bardsley find that coffee addicts show similar foresight¹⁴; Philip Cook and George Tauchen found that when some US counties raised taxes on alcohol, liver cirrhosis fell more sharply than overall consumption, suggesting that it was the alcoholics¹⁵ who cut back most.

我自己的咖啡瘾完全是理性的：我正在写一本新书，随着最后期限的临近，我喝的咖啡越来越多，尽管我已经开始依赖咖啡因。在交稿后，我在度假时采用了突然戒除法，因为我明白，当我在威尔士海岸漫步时，头疼和精神萎靡的痛苦程度要轻得多。

My own addiction was perfectly¹⁶ rational: I’m working on a new book, and as deadlines loomed¹⁷ I drank more and more coffee, even though I was becoming dependent on the caffeine. Manuscript submitted, I went cold turkey on holiday, knowing that the headache and sluggishness¹⁸ of mind would be both less painful and less important while wandering around the Welsh coast.

当然，这只是咖啡因。但即使是吸食海洛因的人也可以在上瘾后，在形势逼迫下戒掉。心理学家李?罗宾斯(Lee Robins¹⁹)发现，在越战期间，几乎半数的美国士兵都吸食海洛因或者鸦片，但很少有人上瘾，近90％的人在回到美国后就戒掉了毒瘾。我自己绝对不想尝试海洛因，但与我的咖啡瘾一样，开始吸毒和尝试戒毒的决定似乎都是对环境的理性反应。

That is only caffeine, of course. But even heroin users can addict themselves and then quit as circumstances dictate²⁰. The psychiatrist²¹ Lee Robins found that almost half of US soldiers used heroin or opium²² while in Vietnam, but rather fewer were actually addicted²³ and almost 90 per cent of those kicked the habit upon returning to the US. I have absolutely no desire to try heroin myself, but it seems that both the decision to start and the decision to try to quit were, like my coffee habit, rational responses to circumstances.

我不得不指出，很多英国内阁大臣在大学期间都抽大麻，但后来都戒掉了。但容我悄声说一句，理性的或许不仅仅是瘾君子，还有政客。

I can’t help noting that a large number of British cabinet ministers decided²⁴ to smoke cannabis at university and then quit later. Whisper it softly, but perhaps not only addicts are rational, but politicians, too