Dear Economist,

有一个关于古罗马末代君王塔尔坎(Tarquin)的传说。一位老女巫走到塔尔坎面前，提出以高昂的价格卖给他9本预言书。塔尔坎对这一提议不以为然。女巫烧毁了其中的3本书，然后提出以原价卖给他剩下的6本。塔尔坎再次拒绝了。

There is a legend about the last king of the Romans, Tarquin. An old witch came to Tarquin, and offered to sell him nine books of prophecy at an exorbitant price. Tarquin laughed at the offer. The witch burned three of the books, and then offered to sell him the remaining six for the original price. Tarquin refused again.

女巫又烧毁了3本，然后同样以最初9本的价格向塔尔坎出售剩下的3本。这一次，塔尔坎担心自己可能会错失一些宝贵的东西，于是以女巫索要的价格买下了剩余3本书。这反映了什么样的需求曲线呢？

The witch burned three more books and offered to sell Tarquin the three books that were left for the original price that she had demanded for nine. This time Tarquin was scared that he might be losing something precious, and bought the remaining three books for the price that the witch asked. What sort of demand curve is that?

克里斯o麦克马洪(Chris McMahon)通过电子邮件发送

Chris McMahon, by e-mail

亲爱的麦克马洪：

Dear Mr McMahon,

忘掉需求曲线吧；这是一个关于经济盈余分配的两方谈判。塔尔坎始终愿意出高价，但同时希望能够还价。女预言家（"女巫"听上去让人不太舒服）则用限制供应的方法来应对，意在推升价格。

Forget the demand curve; this is a two-player negotiation over the division of economic surplus. Tarquin was always willing to pay a high price but hoped to get a bargain. The sibyl ("witch" is such an uncouth label) responded with a supply constriction designed to drive up the price.

塔尔坎可能会认为，这个女预言家只有一位竞争性买家，如果每位买家都只想要3本书的话，这将形成供过于求的局面。而一旦出现两位买家只有3本书可买的情况，塔尔坎明白，他正面临严峻的局面，因而抢先报出了价格。

Tarquin might have thought that the sibyl had just one rival buyer, and if each buyer wanted only one trilogy, that would be a supply glut. Once there was only one trilogy available for two buyers, Tarquin knew he was in a serious auction and made a pre-emptive offer.

还有一种可能性是，女预言家正在解决一个所谓的持久垄断的问题。塔尔坎知道，女预言家可能会以高价向他出售3本书，然后再回头以低价出售另外3本或6本。而通过烧毁6本书，女预言家让自己能够提出一个真正要不要随你的出价。这是一种超前思维，但话说回来，她本来就是在推销预言。

Another possibility is that the sibyl was dealing with the so- called durable monopoly problem. Tarquin knew that the sibyl might sell him an expensive trilogy, and then come back later with a cut- price offer to buy a second or third. By destroying two trilogies, the sibyl enabled herself to make a credible, take-it-or-leave-it offer. Forward-thinking stuff, but then, she was flogging prophecies.