TWO months after it held a general election, Italy has still not managed to form a new government. On April 24th the president, Giorgio Napolitano (who is chosen by members of parliament), asked Enrico Letta (pictured), a member of the centre-left Democratic Party, to cobble together a governing coalition. Even if he succeeds, Italians will probably be asked to vote once again before too long, given the notorious instability of Italian politics. This is hardly ideal, given that Italy is the third largest issuer of sovereign debt (after America and Japan) and is embroiled in a slow-burning economic crisis. Why is it so hard to form a government in Italy? The problem is not new. Ever since Italy reconstituted itself as a republic in 1946, a year after the fall of Benito Mussolini, it has churned through governments. In the 67 years since Italians have had 61 governments (or 62, if you count Mr Letta’s), each one lasting for a little more than a year on average.

This is partly by design. Italy was a divided country in 1946: the south voted in a referendum for a monarchy, whereas the north wanted a republic. One aim of the new constitution was to take proper account of Italy’s many regional variations. Another was to make sure that Mussolini’s rise to power could never happen again. Both of these wishes pointed towards a constitutional system with a weak executive, which is what Italy got. The prime minister needs a majority in both the House of Deputies and the Senate to govern. In a system filled with small parties, this is hard to do. Forming a government, and then keeping it together, depends on the co-operation of a gaggle of groups, often with diverging interests. If a small party falls out with its coalition partners, it can bring down the government.

To this structural explanation must be added a political one: Italy is still a divided place. Since the political rise of Silvio Berlusconi in the early 1990s, his supporters have denounced their opponents as Communists bent on seizing power through a judicial takeover of the executive branch. The other side has, in turn, accused Mr Berlusconi’s lot of being corrupt, criminal and libidinous. Neither group is inclined to seek common cause with the other. On the sidelines stands the Five Star Movement of Beppe Grillo, a comedian, which did well in February's elections but refuses to go into coalition with either side of what it sees as a discredited old order. The result is deadlock. Into this snakepit steps the decent, rather impressive Mr Letta. Past performance suggests he will not last very long.

• What else should The Economist explain? Send us your suggestions.

(Photo: AFP)