WE'RE all fed up with postmodernism now, which isn't surprising, given that the term couldn't even be bothered to define what it was about, but only described itself in terms of what it had just stopped being.

But if it was never entirely clear what it was, other than the thing which came after modernism, there was no question that its central characteristic - even more than its moral relativism, cultural pick 'n' mix and mania for quotation - was the use of irony. The trouble with conveying meaning by the use of words which literally mean the opposite, however, is that after a while no-one knows what anything means. As the American philosopher Richard Rorty put it, "the opposite of irony is common sense".

I prefer to think that the opposite of irony is anaemic, but Rorty's claim is certainly true in politics. If a country has the word "democratic" in its name, for example, it's a dead giveaway that it isn't. Britain's political parties long ago become postmodern versions of their names.

Hardly any Conservatives are at all conservative, most of them being either radical Whigs or advocates of woolly, touchy-feely notions David Cameron is mysteriously keen on. Labour, which in government devotes itself to destroying jobs, became first the party of those who didn't work, by expanding the benefit system until it included everyone, and then the party of tax-dodging plutocrats. The The Liberal Democrats spend their time promoting illiberal measures on lifestyle choices from everything from fast food to fuel use to fox-hunting, while cheerleading for the profoundly anti-democratic EU. Until recently, I would have said that the Scottish National Party stood for what it says on the tin. But since Alex Salmond started constantly redefining independence in order that no-one would be scared by it, so that it now means keeping the Queen, the pound, the BBC, the UK benefits and pensions systems and everything else exactly the same, I'm not so sure.

The latest political grouping to emerge has taken this tendency to new heights of meaninglessness. Labour for Independence, which presents itself as a group of party members working for a Yes vote, has been accused of being an SNP front, rather than a grass-roots movement.

Certainly, there don't seem to be any very prominent members of the Labour party involved in it, and its leader has had to admit that fewer than 40% are actually members of the party - a number that seems even smaller when there are only 80 members to begin with.

Some of them, including the organisation's treasurer, have only just left the SNP to join Labour, while photographs of people holding up a banner promoting the group turned out to contain a large majority of Scottish Nationalists, including several who are actually SNP councillors.

There is, in any case, the intrinsic oddity of a movement dedicated to opposing a central official policy of the party. This is not like lobbying from within a party for some interesting new tweak to the tax code or a change to the law as it affects cyclists; it's as absurd as Greens for Subsidies on Petrol, or LibDems Against PR.

Not, I hasten to add, that there's anything at all inconsistent about people who liked the old-fashioned socialist Labour Party under, say, Michael Foot, also being in favour of independence. In fact, one imagines that this is a fairly sizeable constituency of opinion, even if it is not quite as universal as its members seem to imagine. But if they feel compelled to join a group representing such views, what's wrong with the SNP, which has plenty of lefties in it?

Such people may not like Labour as it now is, and feel that independence will provide the opportunity to reshape both the party and the country along more socialist lines. But their numbers, actual affiliations, and impact on Labour's policy suggest that they are having about as much effect as a Heathite entryist movement (if one could imagine such a thing) would have in the modern Tory party. It's hard, then, to see this as anything other than a way of misrepresenting the Labour party.

The odd thing is that the group appears fake and nonsensical, while clearly representing a kind of political opinion which (even if I don't share it) certainly isn't, and which may indeed be fairly widespread. The idea of, and ideas behind, Labour for Independence are real enough, even if the group itself is a sham.

Rather the opposite charge has been levelled at Better Together, which everybody can see is a real group with real, politically prominent, people in it, but which stands accused of peddling a misleading message. Both critics and some supporters of the No campaign have complained that its strategy is failing to offer anything positive, while scaremongering and concentrating on the dangers and negative points of independence.

I see what they are driving at, but this characterisation is, in its way, as misleading as - to pluck an example from the air - Labour for Independence. An essential part of the job of a group opposing any proposal is to point out ways in which the proposed change may be flawed. When the change is as momentous as independence, that is bound to involve drawing attention to all sorts of things which may become worse than they are under the status quo.

To do so is not "talking down Scotland", but nor is it necessarily to argue only for the status quo. To complain that Better Together offers few positive suggestions for what might be better than both independence and the current arrangements is to ignore what the organisation is for. It's difficult for it to advance detailed plans on, for example, further devolution, because its supporters do not have a shared view.

They are bound together for one objective, which is to point out the deficiencies of the case for independence. In one sense, that can hardly help seeming like negativity, because it's hard to see things as positive when they already exist. But nor does it rule out the option of changes, short of independence, to our constitutional arrangements.

The chief reason why the No campaign is not concentrating on such issues is not that it is tactically less effective than picking holes in the pro-independence case. It is that it is not the question under discussion. The only question is "Should Scotland be an independent country?" And the sole raison d'être of Better Together is to give reasons why the answer is No - or, in other words, to labour against independence.