Market society is sometimes described as a tide that lifts all boats. In many ways, the metaphor is apt. It reminds us that the key to prosperity in a market society is to produce what other people value. Profits normally are not made at other people's expense. People get rich when they market the light bulb, telephone, or computer not because such inventions make people worse off but rather because they make people better off.

People tend to see human commerce as a zero-sum game – a game in which wealth is redistributed but not created. If society were a zero-sum game, though, we would be born in caves. Our teeth would fall out before we turned thirty, and we would die soon thereafter, as our ancestors did when human society was in its infancy. We fare better today because human commerce is not zero-sum. There is a tide. It is lifting boats. In principle, it could lift them all.

What I do not like about the metaphor is its suggestion that the tide lifts us all unconditionally or indiscriminately. There are tides in market society that lift virtually all boats, of course. Market society has given us telephones and light bulbs, and few of us would be better off without them. Nevertheless, as a general rule, material progress does more for some people than for others. The tide lifts the boats it touches; the rest are left behind.