I've just started to give my daughters pocket money, and it's fascinating to see how they deal with it - not the income, that is, but the physical cash itself. The younger Miss Harford hasn't figured out that by tradition, the five-sided coins are worth half as much as the stubby fat ones. (The swaps that her clued-up older sister proposes have to be monitored with some care.) She has also failed to gain any visceral appreciation of the fact that these metal discs can be used to obtain sweets and toys, useful things. She is fascinated by the coins as objects in their own right.

The visceral appreciation for cash will presumably arrive. Cash, it seems, does strange things to us. Ask people to count money and then subject them to pain, and they are more resistant than a control group who have been asked merely to count pieces of paper. Cash is also a social anaesthetic. In another cash- or paper-counting study, experimental subjects were asked to play “catch” in a group comprised of stooges. They never received the ball. The cash counters were less likely to feel socially excluded. Huge bonuses for bankers are both the cause of, and the cure for, their public humiliation.

Physical cash also makes us cautious relative to spending money on credit cards. Drazen Prelec and Duncan Simester, behavioural economists at MIT, ran an experiment in which two groups of subjects were allowed to bid on tickets to sporting events. One group had to pay in cash within 24 hours, the other had to pay with a credit card. The cash buyers offered substantially less - in the case of the best tickets, less than half as much.