When national elections are called, the major political parties — while of course emphasizing their differences through their propaganda — in practice all veer toward the center ground and claim it as their own. We are the ones, each leader proclaims, who can unite the nation.

The argument then turns on the actual character and composition of that center ground, and whether it is itself shifting with the times. For example, in the first exchanges in the current U.K. election battle, the Conservatives scored an early tactical success by insisting that marriage is a key institution for binding society. The Conservatives have made their pro-marriage case by promising some tax concessions for married couples. These are admittedly very modest — a few extra pounds a week — but it is the symbolism that is important and it has touched a chord in voters' minds.

It may seem incredible that something that seemed so obvious to previous generations should need re-stating today. After all, even the very earliest Greek thinkers saw marriage as the underpinning of civilization and the founding stone of a stable society, as well as a highly efficient economic partnership. But it is sadly true that in modern times many sections of fashionable opinion have come to reject the concept. Putting it back on the center ground makes good political sense.