 Since it was founded 21 years ago, this newspaper has been in favour of change to a fairer voting system. In the past, we have voiced support for more radical reform than the alternative vote (aV), which is to be put to a referendum on 5 May. But now we are urging people to vote Yes in four months' time on the merits of the case, because aV would be a valuable democratic improvement on the existing system.  The debate about electoral reform has taken an unexpected turn in the past year. Last May's election produced a hung parliament, the kind of result assumed to be more likely under aV, and hence offered a window into a reformed future. But the arithmetic of the result confronted a number of people, and The Independent on Sunday, with a challenge.  among those who supported a fairer voting system, there were a number who did so because of its presumed consequences, rather than for the principle of fairness itself. Their objective was to keep the Conservatives out, and they assumed that the Liberal Democrats were part of the ramparts against a Tory government. This newspaper half-shared that assumption, supporting tactical voting against David Cameron at the election last May.  That view has been blown apart, which forces electoral reformers to face up to what they think about the intrinsic rights and wrongs of different designs of democracy, rather than trying to second-guess the policy outcomes according to their own political preferences.  This is a paradoxical benefit of an uncertain election result. Electoral reformers ought to be driven back to first principles. To try to calculate the case for different voting systems by party advantage (or disadvantage) is not only wrong, it is also a mistake. although we can guess how past elections might have turned out under aV, based on opinion-poll evidence of voters' second preferences (as we report on pages 14-15, there might have been a hung parliament in 1992 and a Lib-Lab deal might have been more possible last year), people would behave differently under a different system.  Now it is time, therefore, to consider the philosophical or pure case for the alternative vote. In this, we commend the Yes campaign in focusing on the voters rather than the politicians. From the voters' point of view, being able to number candidates in order of preference is a significant improvement on voting with an X. It allows people to express a full range of  