Next week, the main parties will launch their election manifestos. But what purpose do they serve?

The political textbooks will say these documents set out all the parties’ policies, allowing voters to choose between the different offerings. However, that’s about as far from reality as you can get.

Voters are not quietly rational citizens, settling down one evening to read through the manifestos in order to come to an informed decision about which party to support. In fact, hardly any voters ever read a manifesto.

For one thing, the timing is odd. There will be three weeks of campaigning left. Those who design campaigns know that messaging takes a long time. The narrative-setting efforts that the parties make get underway months, if not years, before an election happens.

Each of the main parties already has their core pitch to voters in place, and everything they say is already framed around supporting the agreed narrative – both about themselves and about the others.

Nor do manifestos finally reveal core campaign messages. After all, how long is a print run for those all-important candidate messages to the voters? They are, in fact, already signed off and at the printers – and the manifestos are still to be launched.

Nor do the manifestos inform the parties’ candidates of lines to take and arguments to use at the election hustings. The candidates received their policy briefing booklets several weeks ago and are presumably already word perfect on each and every policy area.

Nor do the manifestos set the programme for policy announcements as the party campaigns unfold. The grids are, in fact, already set in place. The timetable for particular policy announcements is already established and the venues for particular policy launches already reserved.

Despite all these functions that manifestos might fulfil – but don’t – there is still an eager anticipation amongst the enthusiastic followers and participants of political campaigns for their arrival.

Chances are the event may not live up to the level of expectation. Of course, some manifestos may offer rich material for a party’s critics.

Labour’s 1983 manifesto was famously described as “the longest suicide note in history” and, more recently, UKIP leader Nigel Farage, described his own party’s 2010 manifesto as “drivel.”  So manifestos can certainly be interesting – for all the wrong reasons – if they are political nonsense.

But those lessons are learned, and the manifestos we see next week form the main parties will be carefully crafted documents, in which the parties will have attempted to avoid any bloopers at all.

The parties have a choice about how to compile these documents, and the paths they select say a lot about what these documents are, and are not, for.

The route may be about party management. So a manifesto evolution that involves a lot of committees and member consultations and internal debates emerges as a document that binds the party into one, hopefully coherent message, and keeps everyone on board through the campaign.  Voices off can easily be dismissed with ‘but it’s not a manifesto commitment.’

Alternatively the route may be about management by exclusion. The drafting of the manifesto may be kept down to a very small number of people acting in some secrecy.  The final document then has the role of reinforcing the leadership’s command over the campaign and the messaging in the final weeks before polling.

But you still might ask, why are they so late?  In previous elections they were out much earlier.

It’s all about the polls and the Parliamentary arithmetic. While it looks as if securing an overall majority is going to be a big ask, the manifesto potentially assumes a new role. It will become the basis for a post-election negotiation. That will influence what goes in, and what might be left out. The manifesto will determine, to some extent, the framework for any post-election negotiations, and the context for crucial votes in a minority government setting. No avoidable stumbling blocks in the pathway towards compromise are required.

Almost the only people left eagerly awaiting the publication of the manifestos –aside from selected journalists and commentators – are the policy officials in the government departments, who will begin drafting their submissions for new ministers on the basis of manifesto priorities.

Next week, expect some fanfare policy announcements to accompany the manifesto launches.  But it will be a coincidence. Policies can be launched without the need for a full detailed manifesto.

Launch day will come and go. The election won’t turn on the detailed analysis of policy small print.

If done wisely, these documents are instruments in the politics that is still to come. And they are being shaped with that in mind.