If you offer a small boy one candy bar now or 10 tomorrow, he'll grab the one. That's because children have what economists call a "high time preference." They want it, and they want it now. The future is a haze.

The punishing of children must take this into account. One good whack on the bottom can have an effect. A threat about no TV all next year will not.

As we grow older, this changes. We care more, and think more, about the future. In fact, this is the very process of maturation. We plan, save, invest and put off today's gratification until tomorrow.

But street criminals, as economist Murray N. Rothbard points out, have the time preference of depraved infants. The prospect of a jail sentence 12 months from now has virtually no effect.