The slippery slope argument. I'm sure we've all heard it before, on numerous occasions; perhaps we've even used it ourselves, since it seems to be a natural argument for people to give, even people who criticise it in others. And, of course, I'm sure we've all heard it swept aside with those five words: "Oh, that's a logical fallacy!" Okay, so you may wish to claim there are only four words there, since 'oh' is more a sound like 'umm', but the point stays the same, and I'm sure you all agree. This sweeping statement usually is sufficiently derisive as to discredit whoever is using the slippery slope argument (though it rarely makes him change his mind). The question is, are we right in calling it a logical fallacy?
At first glance, it certainly seems to be the case that it is an example of one of my favourite problems in philosopy: Hume's problem of induction. In essence, the problem runs as follows: no matter how many times you see something one way, it doesn't mean it will be that way next time. Hume uses this to show that we have no way to say something causes another; no matter how many times a glass breaks when I drop it, it may not the next glass I drop, simply because I don't know until it happens. To use one final example is swans. Until Europeans came to Western Australia, they believed all swans to be white, because indeed all the swans they had previously seen were white. Yet once they went to Western Australia, what did they see, but black swans! God, I love this problem.
Now, it seems to be the same case with the slippery slope argument, since the argument seems to run like this: If we allow you to push the boundaries this far, this will mean others will push the boundaries further, and eventually everything will end up in the gutter, so to speak. Even if the chap can bring historical evidence to back him up, surely, you may be saying to yourself, this is predicting future events based on past contingencies?? See how Hume turns in his grave, you say! Out, out, damned fallacy!
And yet, this is not all. The slippery slope argument, upon closer scrutiny, in fact reveals itself to be a lot subtler, and a lot harder to refute. Actually, I think it's impossible to refute, but we'll get to that. As is often the case with my discussions, it comes down to a very subtle distinction in understanding or meaning, a distinction which makes all the difference. The slippery slope argument is not saying, "If you let this slide, you'll have a landslide." Well, it is, but not in the way you think. Most people take it to be saying that this will happen immediately and necessarily, which would indeed be a logical fallacy. But the argument runs differently.
The slippery slope argument is the argument that if you let this slide, you set a precedent. You have, irrefutably, shaken the foundations on which we stand; now, certainly, the one who wants to push the boundaries may firmly believe that pushing any further is wrong, but he forgets one thing. What he forgets is that his mind has been formed in an environment with boundaries that go only so far. If he succeeds in pushing the boundaries, the future will be populated by those whose minds are formed by an environment with boundaries that go a little further. The point is, the mindset changes, and a precedent for change in this area will be part of what forms future minds. The slippery slope argument is that if you let this slide, you won't be there to make sure it stops safely, whether you want to be or not. And this is irrefutable. And this can be backed up by historical evidence. It is simply a logical fact that allowing the boundaries to be changed, changes the game.
I shall take one example, the example that, incidentally, started me on a defence of the slippery slope argument, since I used it against a Moral Nihilist philosopher (I know, right, who thought they still existed?!) while discussing this example. In 2011 in the United States, the Institute of Medicine made the recommendation that pregnancy be declared a disease under law, to enable health care provision for contraceptives and the like. Now, here one can make a plethora of easy arguments against this, and one of them is the slippery slope argument: by allowing pregnancy, a natural physical result of a natural physical act, to be considered a disease, a precedent is set. The precedent says that you can say whatever you want under the law, as long as you can get it approved, and it has the desired effect. This is an irrefutable claim, because if future change is opposed the current example can always be used as a "But you did it before" statement.
The slippery slope does not say things will continue to slide, it says you are enabling things to slide further. You may dream of a better world where things will not be changed past a certain point, but it remains that: a dream. In response to the slippery slope argument, one can only quote Yeats: "Tread softly, because you tread on my dreams."