Ireland votes tomorrow (Friday) on two referendum questions: one, relatively uncontroversial, to create a new court of appeal, and one much more interesting, to abolish the Senate, the upper house of the Irish parliament.

The move was promised by both parties to the current coalition government, Fine Gael and Labour, prior to their election in February 2011, although it is opposed by the opposition Fianna Fáil as well as by the Greens and some independents. Opinion polls suggest strong support for abolition, but the large number of undecided voters raises the possibility that many could rally to the “safe” position of voting no – although of course since voting is not compulsory, large numbers will simply stay home.

The Irish Senate is one of the world’s more peculiar upper houses. Its sixty members consist of eleven appointed by the government of the day, six elected by graduates of the country’s two main universities, and the remaining 43 elected by MPs and local councillors from a set of five “vocational panels”, which are supposed to promote social cohesion on a sort of corporatist/Catholic/quasi-fascist basis (this all dates from the 1930s), but in practice are used to reward party hacks.

Unlike such bodies as the Italian Senate, which came close to bringing down a government this week, Ireland’s Senate is mostly powerless. It can only delay legislation, not block it, and it never seems to have won much respect or affection from the voting population. There’s obviously some truth in the claim of Fine Gael’s campaign director that the Senate is “an obsolete institution which has served the interests of the politicians much more than the citizens.”

Mind you, upper houses are often rather odd things. Originally the domain of the nobility (sometimes including the clergy), to counterbalance the influence of the common people in the lower house, they often seem to struggle to find a role in the democratic age.

In principle, the idea of a “house of review”, a place in which legislation can be reconsidered to prevent hasty decision-making, is a good one. “Two sieves are better than one”, runs the old motto. But in practice, most upper houses have not been impartial sieves; they have either been creatures of the government, adding little or nothing to the legislative process, or they have been designed with a built-in conservative bias, therefore tending to obstruct legislation from one side of politics but to offer scant scrutiny to the other.

Upper houses in federations (such as Australia) are usually seen as defending the interests of the states. That can potentially offer a useful role, but because smaller states tend to be more rural and therefore more conservative, equal representation of states can also bring with it a political bias.

If they have no political bias, democratically elected upper houses risk merely duplicating the voice of the lower house or even threatening its legitimacy. Some early democratic reformers suggested holding elections for just one set of representatives and then randomly sorting them into two different houses, but the idea has not caught on.

Australia has six upper houses; there used to be seven, but Queensland abolished its back in the 1920s. All are fully elected; four of them have longer terms (staggered) for members than their corresponding lower houses, providing for greater continuity, while the other two (Victoria and Western Australia) basically just duplicate the terms of the lower house.

Three of the upper houses – New South Wales, Victoria and South Australia – have impeccably democratic credentials, in each case representing the popular vote much more fairly than the lower houses do. The federal Senate and the Western Australian upper house also have proportional representation, but that greater fairness is offset by geographical malapportionment: for federalist reasons in the case of the Senate and for purely political reasons in WA.

Only the Tasmanian upper house is clearly less democratic than its state’s lower house. There it is the lower house that uses proportional representation, while the upper house has single-member districts with a rural conservative bias.

The Senate seems to have established a permanent place for itself in Australian political life, but calls for the abolition of state upper houses are still heard from time to time. None of them seem especially popular, but there is certainly something to be said for the position that even an undemocratic or otherwise unsatisfactory house of review is better than none at all.

Success for the abolitionist position in Ireland tomorrow might perhaps bring the issue on to the radar in Australia, but it seems unlikely that our voters will be given a similar opportunity in the foreseeable future.