Western Australia goes back to the polls in just under a month’s time, on April 5, to re-do its half-Senate election. So of course everyone wants to talk about preferences. In this morning’s papers you can read (in the Fairfax press) about the prospect of Labor shafting the Greens, and (in News Corp) about Glen Druery threatening that his preference harvesting could cost the Coalition a seat.

To understand either point, it’s necessary to get something straight about the basics of the Western Australian Senate vote.

Every person and their dog are likely to stand (nominations close next Thursday), but almost without exception the serious and semi-serious candidates will fall into five groups: the Coalition, Labor, the Greens, a variety of broadly left-wing minor parties (Sex Party, HEMP, WikiLeaks, etc), and a larger number of broadly right-wing groups (Palmer United, Liberal Democrats, Christians, Shooters, Family First, etc.)

Last year, when they ran the election the first time, the Coalition had fractionally over three quotas and the right-wing minors just over one quota. Labor had a bit less than two quotas, the Greens about two-thirds of a quota and the left-wing minors the remaining one-third.  So although the original count and the recount gave different results, in terms of the Left/Right balance they were the same: four to the Right (three Coalition and either a Palmer or a Sports Party — that’s “or”, not “and” as the News Corp story has it) and two to the Left (either two Labor, or one Labor and one Green).

It’s generally assumed that for the re-election there’ll be a swing away from the government, so the overall Left should be favorred to pick up a seat at the expense of the overall Right.

Unless the pattern of voting changes radically from last year, that would mean the second Labor candidate and the Greens’ Scott Ludlam would both get up, while on the Right there would be a close contest between the third Liberal and whoever came out at the head of the pack of right-wing minor parties.

So what Druery is saying is basically correct: if the right-wing minors preference one another tightly, the Liberals certainly “might struggle” to again get a third candidate elected. (It’s also possible that the Nationals, who run a separate ticket but whom I’ve included in the Coalition total, would be in the mix.)

But there’s a bit more to Druery’s ambitions than that. His preference strategy also involves trying to convince minor parties that they have a common interest that transcends ideology, so that left- and right-wing minor parties should preference one another ahead of their respective major parties.

And here’s where the Labor v Greens dynamic comes in.

“Transferring a seat from the Greens to a minor party can only make Labor’s position worse …”

Unless there’s some large and unexpected shift, there’s no chance of the left-wing minor parties getting near a quota between them. The Left’s seats should be shared between Labor and the Greens: either one each (as in last year’s recount), two-nil (as in the original count) or two-one (if the left picks up ground in aggregate).

So if Labor chooses to distance itself from the Greens by directing preferences to, say, the Sex Party, that should have no effect. It’s not impossible that a left-wing minor party could sneak ahead of the Greens if there was a large Labor surplus, but it’s much more likely that Ludlam would still get up — provided those preferences go to the Greens ahead of any of the parties on the Right.

That proviso hasn’t always held up. Most famously, in Victoria in 2004, the ALP directed preferences to Family First ahead of the Greens, electing Steve Fielding. Despite that experience, there are evidently many on the Labor Right (or even, if Fairfax is to be believed, on the Left) who would happily do the same again.

In terms of Senate numbers, that makes no sense. Transferring a seat from the Greens to a minor party can only make Labor’s position worse (because Labor can’t get a majority without the Greens, whatever happens). But lack of sense is not necessarily a fatal obstacle.

It’s the same lesson that was learned from the Queensland Liberal Party’s warfare over One Nation preferences 15 years ago. Participants in the debate claimed to be arguing about what made better tactical sense for the party, but in reality they were arguing about whether or not they felt themselves to be philosophical kin to One Nation.

Similarly, Labor’s tacticians will have ingenious rationales for preferencing the Right, but what they really boil down to is that they hate the Greens and want to express that hatred. (Or, more cynically, that they’re convinced the electorate hates the Greens and want to show that they feel the same.) They don’t really have a preference strategy, they have preference symbolism.

Even assuming Labor’s votes still end up with the Greens, the risk of the anti-Green agitation is that some of the left-wing minor parties will be more inclined to listen to Glen Druery’s siren song and divert their preferences from the Greens to the likes of Palmer, the Christians or the Sports Party. And if that happens, the Right’s chances of again walking away with four senators would be much improved.