Dear Economist
Dear Economist,
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I have a drawer full of odd socks. Where do the missing socks go?
Christian Turner, Washington DC
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Dear Mr Turner,
Like most investments in physical capital, your sock supply is depreciating. Depreciation happens. I suggest that you should work out how to minimise the damage, rather than questing after the lost socks.
The problem is simple: each half of a unique pair of socks is a perfect complement to the other half. The marginal value of the first sock is close to zero, unless you favour unconventional dress. The marginal value of the second sock is a matching pair of socks. The result of a lost sock is in fact the loss of two socks.
This problem also plagues machines: when one component fails, the entire machine may need to be scrapped. The solution is to make interchangeable parts, so that the damaged piece can be replaced. Interchangeability dates back at least to Gutenberg and the printing press in the 1450s, but formidable technical problems meant that interchangeability didn’t become common until the assembly lines of the early 20th century. Generations of engineers knew that the struggle across the centuries would eventually pay economic dividends. You, on the other hand, do not need to wait for some hard-won technological breakthrough. You should have no difficulty providing interchangeable parts for your sock drawer. Throw out your pre-industrial inventory, then go out and buy two dozen pairs of identical socks at once.
I personally find this method works extremely well. What you lose in sartorial flexibility you make up in a less wasteful pattern of sock depreciation, and a vastly quicker search of the sock drawer each morning. Your socks will still vanish mysteriously, but you are far less likely to ask metaphysical questions about the phenomenon.
袜子不成双，怎么办？
亲
爱的经济学家：
我有满满一抽屉不成双的袜子，失踪的袜子去哪儿了呢？
克里斯蒂安?特纳(Christian Turner)，美国华盛顿
亲爱的特纳先生：
就像大多数实物资本投资一样，您的袜子供给在贬值。贬值总会出现。我建议您想办法将损失降至最小，而不要寻找那些丢失的袜子。
问题很简单：每双独一无二的袜子中，每一只都能与另一只完美搭配。第一只袜子的边际价值接近于零，除非您喜欢以另类的方式穿袜子。第二只袜子的边际价值是一双成对的袜子。其实，丢一只袜子的结果就等于两只都丢了。
这个问题也困扰着机器：当一个零件失灵时，整台机器或许都需要报废。解决办法是生产通用零件，以便受损的零件可以得到更换。通用零件至少可以追溯到15世纪50年代的古腾堡和印刷机时代，但由于面临艰巨的技术问题，所以直到20世纪初出现了装配线，通用零件才变得常见。历代工程师都知道，几个世纪的努力最终会产生经济回报。另一方面，您用不着去等一些来之不易的的技术突破。您应该可以毫不费力，就为您装袜子的抽屉配上“通用零件”。扔掉您的陈年旧货吧，然后去一次买上两打一模一样的袜子。
我自己觉得这个办法极其管用。袜子的式样减少了，但您得到的补偿是，袜子贬值产生的浪费也减少了，而且每天早晨翻抽屉找袜子的速度也快多了。您的袜子仍旧会莫名其妙地失踪，但您就这一现象提出形而上问题的可能性也低多了。
