If you look up ‘slippery slope’ in any philosophy or logic textbook it will tell you that the slippery slope is a logical fallacy. All of the ones worth reading will and most of the bad ones will, too – because the Slippery Slope is in fact a logical fallacy.

Trouble is, it’s also literally a political reality.

How can it be both? Let’s look at why Slippery slope is a fallacy.

Bob is a Reasonable Man. ^(TM) Bob does reasonable things because he reasons before he acts. When Bob comes to the top of a slippery slope, Bob reasons that he shouldn’t go any further because doing so risks a bad fall. Bob goes another way and avoids the Slippery Slope.

Since any Reasonable Man^(TM) can see the danger and avoid it, the Slippery Slope isn’t a danger merely to approach. In fancier language, the reasonable person can always stop in time so there is no danger of continuing a downward slide.

That’s the theory. It doesn’t deal well with the problem of someone failing to recognize the danger and continuing past the point of no return – but nothing’s perfect and as fallacies go, it’s serviceable because it’s in essence correct.

But notice that the explanation deals only with the one reasonable person. Let’s see what happens with a bunch of reasonable people.

The Quilting Bee Baseball team is running to their game. They are all reasonable people who do reasonable things because they reason before they act. So when Tom, Dick and Harry get to the top of the Slippery Slope, they stop to consider the matter. Unfortunately, momentum isn’t particularly reasonable and the rest of the team runs into the three who abruptly stopped, sending everyone headlong down the hill.

Political momentum, just like physical momentum, can be a powerful force. Worse, a body politic is usually larger than a baseball team. Where maybe the trio could stop soon enough to stop the others safely in our example, that rarely works with a few hundred people upset over something. And you can pretty much forget it for several thousand who have become convinced that X policy is the best thing since white bread and aren’t listening any longer.

Sometimes, it’s a long downhill slide like the assurance that abortion wouldn’t lead to euthanasia – it took less than a decade which is historically fast but considered slow in contemporary politics. Other times it’s not even a slope – it’s a cliff and no amount of reason is going to stop the momentum racing to the edge.

Reasonable Man Bob, spotting the danger, considering his options.

Er, never mind. Bob doesn’t seem to have any options.

Danged Slippery Slope!