How marriage is like coal mining.

The economic mysteries of daily life.
Sept. 16 2006 7:51 AM

A Marriage of Convenience

How matrimony is alarmingly like coal mining.

I am back from a brief vacation, and that always brings fresh perspectives. I notice new things about life in the office and life at home. In both cases there are the petty annoyances. At the office, I find myself increasingly irritated by the loudspeaker that bellows a prerecorded, and irrelevant, security announcement whenever I lock my bicycle to the bike racks. At home, I have to put up with my wife's predilection for unreasonably healthy eating.

Of course, in both cases there is give and take. In exchange for putting up with the electronic honking of the security system and for the turnip soup, I'm allowed to take my own little liberties. My salary is not docked if I turn up to work late after a trip to the dentist, but I wouldn't want to try the trick if I were billing by the hour.

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As at work, so in love. When I was dating I'd work out, brush my teeth after every meal, and always wear clean underwear. Now that I'm married I do those things too, of course. Mostly. But I suspect that occasional lapses would, within reason, go unpunished.

What the marriage and the job contract with the Financial Times have in common is that they are long-term arrangements where, in principle, a series of short-term arrangements might do. I have in the past written for the FT as a freelancer. Nobody shouted at me for parking my bike, but nobody paid me for going to the dentist, either.

There are also many short-term alternatives to "till death do us part." Some cultures even offer temporary marriages: Pagans sometimes marry for a year and a day, renewable by mutual consent, while Shiite Muslims can arrange fixed-term marriages which are as brief as an hour. Of course, most people who rent motel rooms by the hour don't bother with the concept of marriage at all.

So, why are some partnerships brief and some permanent? Consider—as MIT economist Paul Joskow did in the 1980s—American coal mining and the coal-burning power industry. On the West Coast, coal mines and coal-fired power stations married each other, either by merging or by signing 30-year contracts with great detail about how disputes were to be dealt with.

On the East Coast, free love prevailed: Power stations did not necessarily locate near the mine head, and they often bought coal on the spot market or through relatively short-run contracts.

Professor Joskow is in no doubt as to the reason for the difference. All East Coast mines produced very similar coal, they were able to operate profitably at a small scale, and they were linked by a rich web of transport connections. A power station could pick and choose from month to month which mine would supply it.

On the West Coast, the mines were much bigger and each one was unique. Power stations had to tune themselves to deal with a specific mine's output and would generally locate themselves near the mine head. In such a situation, it would be easy for the mine to exploit the power station by suddenly jacking up the price of coal. The best thing, then, was a merger of interests so that both were on the same team.

Joskow's explanation surely tells you something about when to be a freelancer—perhaps even when to stop playing the field and get married. Like East Coast coal mines, it can be attractive to be footloose and fancy-free as long as you always have alternatives and as long as you are not required to make serious investments that are specific to the relationship. My own marriage was swiftly followed by a relationship-specific investment. She's nearly 2 and a half.

Tim Harford is a Financial Times columnist. His latest book, The Logic of Life, will be published in paperback on Feb. 10.