How should a democracy be judged? Some argue that the freedom of the press is the determining issue; others, the probity of its politicians; others again, its citizens' happiness. Well, here's another suggestion. It has not, to my knowledge, been much considered by think-tanks and modern commentators, though for ancient Greek and Roman political thinkers it was central. Neither does it feature in the cost-benefit analyses of economists, though most people would say it was essential to the good life. The alternative measure is the extent to which democracy is conducive to friendship.

At first, the suggestion might appear odd. It seems natural to assume that a democratic society is automatically a friendly one: its characteristic elements, like freedom of association, could only contribute to the flourishing of friendship. Of itself, therefore, friendship might be thought as simply a by-product of democracy, if one that is highly desirable.

Mark Vernon is the author of The Philosophy of Friendship (Palgrave Macmillan, 2005). His website is here

However, friendship is a more interesting test because some of democracy's highest values are actually at odds with it. In short, friendship puts the humaneness of abstract democratic ideals on the spot.

One obvious point of tension is between the egalitarian principles of democracy and the individual partiality of friendship. Democracies treat all citizens the same: everyone is equal in the eyes of the law and has the right to one, and only one, vote. Human rights too are absolutely universal or they are worthless. Friendship cuts across this because it is not universal but is defined by its particularity. To say "you are my friend" is meaningless if it does not imply that I regard you above the rest. One would do something for a friend that one would never dream of doing for someone else; friends act for each other out of preference and loyalty not disinterest.

Democracies, therefore, have an ambivalent attitude towards friendship. It is fine in private but deeply suspect if and when it is seen to play a part in public life. Then politicians are accused of nepotism, which in a way is counterproductive since so-called "cronies" are likely to give much to public life by virtue of their loyalty. Alternatively, companies can end up in court if they are seen to appoint without due regard for equal opportunities, for all that knowing someone before you appoint them is perhaps the only way of being sure they can do the job.

A second area of conflict between the values of friendship and democracy concerns justice. For Aristotle, justice could be thought of as "failed friendship". It is when individuals cannot resolve their differences amicably - note: amicably - that they turn to the law. It aims to solve their problems according to a depersonalised conception of fairness. Or, when friends can no longer "hold things in common", as one Greek saying defined friendship, they ask the courts to divide their possessions and rule over them. Thus, for Aristotle, rectificatory justice is a pragmatic good, since people will always fall out. But it is not an absolute good, because if all people lived well, justice would simply be a common character trait implicit in friendship.

In a democracy, however, justice is an absolute good: it must be done and be seen to be done. Again, therefore, democracy can nurture a suspicion of friendship, thinking that it is a way of doing things characterised by questionable commitments and opaque affections, not the transparent, transcendent fairness of justice. The downside of idealising justice in this way is the speed with which people turn to the law when resolving personal disputes. Hence, perhaps, the fact that the most mature democracies are highly litigious. And as those involved in family law know, a litigious culture is one in which friendships struggle to thrive.

There are other points of tension between democracy and friendship. For example, democracies tend to nurture utilitarian approaches to politics, based upon trying to establish the greatest happiness for the greatest number. Friendship, though, abhors "felicific calculus", preferring to build relationships. Might this not suggest a reason why increasingly affluent democracies become increasingly unhappy places to live?

True, egalitarianism, justice and economics-driven problem-solving are hugely valuable and underpin a very many great goods. However, that they are valued because they are impersonal is double-edged. The great paradox for democracies espousing these universal ideals is that unless their sovereignty is tempered they become dehumanising and tyrannical. And friendship, without which the good life is simply impossible according to Aristotle, suffers.

For ancient philosophers friendship was a political problem too. They understood that it could be corrosive of civic life. But they adopted a different approach. Rather than putting all their efforts into upholding universal ideals that tend to sideline and undermine friendship, they sought to promote ideals for friendship too. For Plato, the best friends are truth-seekers. For Aristotle, friendship schools the greatest virtues. For Cicero, they are intent on the greater good. Is it not time for us to do likewise and re-establish a high place for friendship?