The police investigation into the botched terrorist attacks in Glasgow and London reminded me of the classic Prisoner's Dilemma. In this famous game, police don't have enough evidence and are trying to get two prisoners, say Bilal and Sabeel, to confess. If one of them confesses he will be let off but the other will spend his life in jail. If neither confesses, both will go free. If both confess, then both will have to spend seven years in jail. The logical selfish strategy is to confess, betray your partner, and hope that he won't. The altruistic path is not to confess. The best strategy is to collaborate--neither should confess.

Oddly enough, Prisoner's Dilemma is relevant to our nation's hazy moral health—to Pratibha Patil's ambivalent record; to government employees who insist on bribes; and landlords who renege on promises—indeed, to the question I posed in my last two columns: 'Are people good only because of the fear of punishment?' Draupadi asked this question in Mahabharata and Robert Axelrod, the American social theorist, speculated in the early 1980s about how to get strangers to cooperate and be nice to each other in capitalist democracies. He used this game to show that if people only pursue the selfish strategy they undermine the collective good.

Axelrod conducted a Prisoner's Dilemma round robin tournament in which contestants played 200 games with one player and then moved to the next, the objective being to minimize the time in jail. The reason for repeating the game was to simulate real life where people meet each other repeatedly. The winner was Anatol Rapoport, whose strategy was neither altruistic nor egoistic but 'tit-for-tat', what we call 'nehle pe dehla'.  'Tit-for-tat' means don't confess (be nice to the other prisoner) on the first move, but after that do what the other player does. Axelrod re-ran the tournament; 'tit-for-tat' always won; cheaters always lost.

What this game teaches about life is that one ought to be nice when one encounters strangers. 'If you are nice, others will be nice to you', my aunt used to say. If the other person is not nice, then 'tit for tit' is the wiser response so as to not to be taken advantage of. This principle of reciprocity keeps cheats in check in society, whereas Gandhi's (and Jesus') teaching about turning the other cheek sends them a wrong signal that cheating pays. All societies have evolved principles of dharma in part to make people cooperate.

Moral rules are grounded in human self-interest; they teach one to adopt a friendly face to the world but not allow oneself to be exploited. Reciprocity does not apply to those one loves, of course. If the prisoners care for each other like brothers they will instinctively think of minimizing the time both will spend in jail. But in large cities like Delhi or Mumbai, where we are surrounded by strangers, the principle of reciprocity is the guiding principle of civilized existence. This pragmatism also runs through the Mahabharata but  is absent in the Left's moralizing.

It's a pity we use 'tit for tat' in unflattering ways. Congress used it last month to defend its retaliation for the BJP's smearing of its presidential candidate. This newspaper's headline read on August 6, 2006: 'Tit for tat: India, Pak play spy games, expel envoys'. New York Times called Pakistan's firing of the Abdali nuclear missile 'tit for tat' in response to India's Prithvi on March 26, 2003. It's a pity I say, because 'tit for tat' is the reciprocity inherent in decency, friendship, trust and eventually civilization.