Logic, logical fallacies and fallacious logical fallacies, are the meat and potatoes of lawyers.  Without them, we would have little to say beyond, “does not!”  Believe me, that won’t get you very far.

One of the favorite arguments is the trusty “slippery slope.”  The slippery slope argument is that one “action will initiate a chain of events culminating in an undesirable event later.”  The problem with the slippery slope is that it fails to establish or quantify the relevant contingencies. 

Paternalistic pedagogues like to argue about things like this, the relative merits of rhetoric and logic.  Over at PrawfsBlawg, Rick Hills offers a screed against the slippery slope:

So why do patently unconvincing slippery slope arguments grow like black mold in a leaky attic every time a court makes a decision about sexuality? I think that we’ve used slippery slope arguments so carelessly that we are losing our intellectual capacity to draw fine-grained conceptual distinctions. Once one starts invoking the essential similarity of one thing to another, one can’t stop: The temptation to assert foolishly that logical consistency requires elision of any distinction not crudely cut with a meat cleaver becomes an addictive habit. (E.g., “You think animals have rights? Why don’t you let them vote?” “You think invading Iraq was a good idea? Why not China?” And so forth).

Vivid imagery aside (“like black mold?”), the slippery slope argument has been around forever and has yet to undermine our “intellectual capacity” any more than American Idol or the Gong Show (which, I hear, is making a comeback).  It can’t be that “patently unconvincing” or we would have given it up long ago.

Eugene Volokh, explains:

It’s true that arguments that it will be logically impossible to distinguish a future case from this case are usually very weak. Very few distinctions are logically impossible.

But slippery slope arguments endure partly because they are often cast, much more plausibly, as arguments that if X is done, it will become more likely that Y will be done — not that X and Y can’t be treated differently, but that they won’t be treated differently. These arguments aren’t about logical consequences, but about psychological consequences (plus some other consequences). And as such they can’t be rebutted simply by pointing out that a distinction could be drawn.

So, there may be a tendency to be a tad hyperbolic in the presentation of the slippery slope argument, perhaps being a little more absolute in the view that bad things will most assuredly follow, but that doesn’t mean that opening the door doesn’t make it more likely.

The other reason that slippery slope arguments endure is that slippery slopes do often seem visible. I say “seem” because it’s often impossible to tell for sure whether X increased the likelihood of Y, or whether Y would have happened in any event. But sometimes there’s good reason to think that slippage has happened, often despite the express insistence of backers of X that of course X won’t help lead to Y.

Eugene provides examples where promoters of a position assert that there’s no slippery slope in sight, and yet time proves them wrong.  The law tends to move in small steps rather than giant leaps.  Each step taken in a particular directions makes the next step that much easier to take.  Given enough time, the law often finds its way to a particular outcome that was raised, and dismissed, when the first step was taken.  By the end of the journey, the final step seems quite reasonable because of the baby steps taken to get there.

Slippery slope arguments also have a great deal of superficial appeal.  Lawprofs may be inclined to argue about the “conceptual ledge” where the slope stops being slippery, but people of more common intellect (which includes lawyers, judges and jurors) don’t stress over such details.  Given the 12 seconds involved in most decision making, superficial appeal is a fine way to go.

There are a bunch of issues floating around lately that are subject to slippery slope arguments.  Will a constitutional right to same-sex marriage inexorably lead to a constitutional right to polygamy?  Will a constitutional right for individuals to bear arms lead inexorably to a constitutional right of felons to own guns?  The obvious answer is no, not “inexorably”.  But it does make it more likely, and present some difficult logical obstacles for a court on the next case, when the envelope gets pushed a little farther.

So while the lawprofs both recognize, and ridicule, the logical fallacy of the slippery slope, the fact remains that while there is no guarantee that threats of dire consequences will ultimately come to pass, they sometimes do. It’s mistake to dismiss the slippery slope argument too quickly. 

If I happen to see a camel’s nose peeking under my tent, I plan to give it a decent smack on the snout.  Unless I happen to be standing on the south side of the camel, in which case I’ll be pushing that rump as hard as I can.  It would be a lot easier if the camel happened to be standing on a slippery slope.