SEEN from the state's point of view, multiple citizenship is at best untidy and at worst a menace. Officials would prefer you to be born, live, work, pay taxes, draw benefits and die in the same place, travel on one passport only, and bequeath only one nationality to your offspring. In wartime the state has a unique call on your loyalty—and perhaps your life. Citizenship is the glue keeping individual and state together. Tamper with it, and the relationship comes unstuck.

But life is more complicated than that. Loyalty to political entities need not be exclusive: indeed, it often overlaps. Many Jews hold Israeli passports in solidarity with the Jewish state (and as an insurance policy), alongside citizenship of their native country. Teutons may be proud to be simultaneously Bavarian, German and European. Irish citizens can vote in British elections. The old notion of one-man, one-state citizenship looks outdated: more than 200m people now live and work outside the countries in which they were born—but still wish to travel home, or marry or invest there.

The wrong response to this is political protectionism, with states forcing citizens to choose one nationality only, or hampering their right to multiple passports. This seems an odd approach, given that citizenship is so easily acquired. In some countries it is, in effect, on sale. In others, such as America, it may be an accident of birth, with no conscious choice involved. Rather than making a fetish out of passports, a better approach would be to use residence (especially tax residence) as the main criterion for an individual's rights and responsibilities. That encourages cohesion and commitment, because it stems from a conscious decision to live in a country and abide by its rules. The world is gradually moving in this direction. But many states (mostly poor and ill-run) resist the trend and some rich democracies like the Netherlands and Germany are trying to curb it (see article), offering a variety of excuses.

One longstanding worry, the security of the state, seems out of date in modern countries. Citizenship mattered in the days when defence relied on conscription. But modern warfare does not require armies of ill-trained conscripts. Few countries now rely on mandatory military service and those that do are mostly winding down the draft. Citizenship is no guarantee of loyalty: history's worst traitors have been true-born citizens. Many of those ready to fight most enthusiastically for a flag will have gone through hell to get to their country.

That leaves a host of political and financial problems that governments associate with non-citizens: they dodge taxes, grab benefits or retain retrograde habits from their countries of origin. So they sometimes do. But countries that want to clamp down on tax evasion, protect their national language, or deter such foreign customs as forced marriage, should do so through specific laws tailored to these ends, rather than relying on the symbolic power of citizenship. America's policy of taxing its citizens wherever they live seems especially perverse; it is an accountants' charter. As for benefits, residency is surely the key. Live and pay your taxes in a country—and you should then be treated in the same way as any other resident, and better than a citizen who has lived overseas and not paid up.

Vote often

The thorniest problem for a residency-based system is voting—a right that has long been linked to citizenship. But there is room for compromise here. In France and Italy, for instance, citizens who live permanently abroad (often with dual nationality) have voting rights. That makes sense. Conversely, countries should give long-term resident non-citizens the right to vote, at least in local elections. European Union countries already allow that to each others' citizens.

But looking at multiple citizenship purely on the basis of costs and problems is wrong. It also encourages links between diasporas (often wealthy and well connected) and their home countries (usually poorer), to the benefit of both. Multiple citizenship is inevitable and, at heart, rather liberal. Celebrate it.