Wednesday, 13 November 2013

The slippery slope argument

The other day our neighbour asked if he could borrow a shovel. Despite the risks, we agreed. Now we're getting 5 or 6 people a day at the door every day wanting to use our shower, borrow the car for a week, camp in our yard etc. Its ruining our lives, but obviously we have to agree. We are the ones that knowingly headed down this slippery slope so we can hardly stop now. Who knows where it'll end? We should never have loaned the shovel.

It turns out that loaning stuff is just like doing drugs. Fortunately, we already knew that story. You start out thinking a cup of tea or coffee sounds pleasant. With sugar? Oh all right then. But once you start saying yes to such things, well logic takes over doesn't it? Next thing, you're accepting beer, then wine, whisky and pot and then, well how could you possibly say no to mainlining heroin? That's why we've never ever tolerated tea or coffee in the house.

My point of course [swings sledgehammer] is that the slippery slope is a logical fallacy. It simply does not hold water as a generic argument because it can be refuted by silly examples like the ones above. It works OK as a joke, but we shouldn't take it seriously in a debate.

Unless a plausible mechanism is clearly described by which doing A makes it more likely that B will also occur. But even then, all that's really happened is that another potential consequence now needs to be factored into the decision. So, yes, there is a risk that if I start drinking tea I'll end up all the way down at the bottom of the slope as a junkie. But if the subjective probability of that is quite low, I might just take the risk.


  1. One such mechanism noted here.

    It's kind of a running theme at Offsetting; haven't bothered hitting mechanism in each and every post. A few candidates:

    1. Public health campaigners move on to the next target down the line as grant funding on past targets dries up.
    2. Marginal cost of extending a control mechanism to a new domain is lower than establishing it in the first place so it is likely that when it starts, it will extend.
    3. Where the public would oppose the full suite of controls if offered at one go, they're less likely to oppose many small steps leading to the same goal. So if you want to ban tobacco and it is 1978 you only ask for voluntary non-smoking sections as a sensible moderate position. Then mandatory ones. Then smokefree restaurants and public buildings. Then smokefree anywhere a kid might be. Then Smokefree NZ by 2025. Anti alcohol campaigners have already started talking about a .03 BAC limit. I don't think it is nuts to believe that public health campaigners want far more control over our consumption decisions than they're letting on. It's consistent with the evidence. And it isn't a fallacy in this case.

  2. Ironically, a couple of hours after posting this, we ended up with a stranded couple camping in our yard!

  3. Did you offer them some tea? Or perhaps some smack?

  4. Yes there was a cup of tea in the morning, and sure enough Lynne ended up driving them home which was a fair old schlep.