That's why today's news of research at the University of Leicester, looking into Liberal movers into other parties over the last century, is so interesting.
Alun Wyburn-Powell, who teaches at Leicester, has analysed Liberal defections over the twentieth century and found that Liberals moving over to the Conservatives stayed much happier than those going off to join Labour.
Why? Because the Conservatives had much more in common with them in terms of outlook, social life, education and all-round alikeness. Birds of a feather and all that.
It has always been thus. Joseph Chamberlain's Liberal Unionists of the 1880s and 1890s, who left the Liberal Party over the issue of Irish Home Rule, had much more in common with the emergent 'Villa Tories' on the benches opposite them than they did with pushy 'labourist' and 'radical' Liberals from England's smaller cities and the so-called 'celtic fringe'.
Want to know why the Coalition probably won't break up? Look to the dinner party, the wine menu, the private (or grammar) schooling and the South-West London houses.