In his dissent to the Supreme Court’s landmark ruling on same-sex marriage, Chief Justice John Roberts offers a familiar ‘slippery slope’ argument:

“Although the majority randomly inserts the adjective ‘two’ in various places, it offers no reason at all why the two-person element of the core definition of marriage may be preserved while the man-woman element may not. Indeed, from the standpoint of history and tradition, a leap from opposite-sex marriage to same-sex marriage is much greater than one from a two-person union to plural unions, which have deep roots in some cultures around the world. If the majority is willing to take the big leap, it is hard to see how it can say no to the shorter one.” (emphasis added)

I think there are good responses to Roberts’ argument, though I don’t intend to pursue them here. Instead, I would like to make a few observations about ‘slippery slope’ arguments in general.

Slippery slope arguments are, it seems to me, characteristically modern. The history of the expression suggests this: according to Etymonline.com, the term ‘slippery slope‘ was not used in this sense until 1844. My own experience studying early Jewish and Christian texts, which rarely if ever offer ‘slippery slope’ arguments, also confirms this. (This is, admittedly, rather limited evidence, and I would be happy to be shown otherwise). How, then, do slippery slope arguments work, and what do they teach us about the difficulties of reasoning in our post-modern era?

A slippery slope argument is a way of testing explicit general principles against our moral intuitions about particular cases. In the example above, Roberts offers two particular cases that, he presupposes, the majority would want to distinguish: same-sex marriage and polygamy or plural unions. The principles to which the majority appeals — e.g. that the liberty to enter into marriages is implicit in the right to autonomy — cannot, Roberts argues, explain why the first case should be protected but not the second.

To this extent, a ‘slippery slope’ can be formulated quite abstractly as a logical relation between premises and conclusions. But the image of a slippery slope also suggests something more dynamic: the risk of uncontrollably sliding down it. A slippery slope argument thus typically implies a prediction about a looming future. ‘If we as a society let this principle determine our decision about same-sex marriage,’ it says, ‘then tomorrow it will be polygamy,’ or incest, or whatever. The sense that this slide is uncontrolled or inevitable reflects, I think, the fact that these consequences follow logically from the principle in question.

Yet if the rational consequences of a decision are already apparent today, why does it take any time at all to slide down the principle’s slope? For the obvious reason that neither individuals nor societies always make ethical decisions by following a few clear principles to their logical conclusions. Very often the implications of our principles are not clear to us. Consequently, very often we hold multiple contradictory principles at once. Moreover, very often we do not make decisions on a principled basis at all, but rather rely on our more or less unexamined moral intuitions. The vagueness, contradiction, and intuition of our individual thinking are all multiplied in the context of social decision-making, where they are exacerbated by a host of other complexities: power and violence, money and democratic process, etc.

Now slippery slope arguments offer a linear picture of the reasoning process: reasoning proceeds only from principles to cases. On this picture, the vagueness, contradiction, and intuitions that slow down the march of a principle are only signs of irrationality. No wonder the slope of accepting a principle is so slippery!

They also presuppose that rational principles may be effective in overcoming these irrationalities — not least through the mechanism of Supreme Court decisions! And there is surely a great deal of truth to this. Not least because modern people do characteristically reason from principle to case, these principles are genuinely effective in the real world, overcoming contradictions and altering moral intuitions; changing our social customs, government policies, and laws. From the French Revolution to the abolition of slavery, from the Civil Rights Act to the legalization of same-sex marriage, to be a post-Enlightenment liberal is to accept that ethical principles can be historically effective. This is why slippery slope arguments are not only logically valid but may be empirically predictive — at least in a context like ours.

But what slippery slope arguments tend to neglect is that this picture of reasoning is also not inevitable. It is possible to be more sure about your intuitions than you are about your principles. It is possible to be more sure, for example, that incest or polygamy is wrong, than you are that the principle of autonomy should extend to them. And though I have just said that modern people tend to reason from principle to case, I still believe that most people most of the time intuitively approach ethical questions as a complex negotiation between principles and intuitions. This is confirmed by the truism that same-sex marriage has gained such rapid acceptance because people have simply gotten to know their same-sex neighbors. More and more Americans have found they can’t say ‘this is wrong’ in this particular case; but they are not necessarily reasoning directly from a principle like individual autonomy, as our conservatives fear. The growing acceptance of same-sex marriages on the evangelical left, for example, has not necessarily been accompanied by an acceptance of pre-marital sex.

The wiser course is surely to recognize that while intuitions are fallible, so is the application of principles. In fact, the zealous pursuit of a principle to its logical conclusion, which a slippery slope argument presses, is often most characteristic of fundamentalists and ideologues. Their logical ‘consistency’ often masks a deeper irrationality and violence, one that the vagueness and contradiction of our more common sense forms of reasoning manage to avoid. (This argument is a ‘conservative’ one, in the old-fashioned sense associated with Edmund Burke). Ironically, then, those who make slippery slope arguments often underwrite the very habits of thinking that would lead to their dire prophecies being fulfilled!

Moreover, when such people assume that everyone probably thinks in the same principled way that they do, they can easily come to view the kinds of contradictions that are characteristic of our actual reasoning processes as not only sub-rational concessions or compromises, but even worse, as something deceptive and sinister. ‘Give them an inch, they’ll take a mile’ — this particular case is really just the first stage of a whole ‘agenda’ (an agenda which is usually only the mirror image of one’s own). And again, since modern people do often think this way, on both the right and the left, there are some grounds for this suspicion.

Kennedy’s majority opinion represents, however, quite a different style of thinking. He is, oddly enough, quite a conservative thinker. His opinion does not begin by laying down a principle of autonomy that he then applies rigidly, come what may. Rather, he recounts a slow and often painful social learning process, driven as much by the examination of particular cases as by the application of general principles. If one assumes that intuitions about particular cases contribute nothing to ethical reasoning, then indeed a slippery slope may loom.

But why make this assumption? Why not trust that there are other modes of ethical reasoning already in play in our society? And where they are not, let us seek to become the kind of society that attends as much to particulars as to principles, a kind of society different from what a ‘slippery slope’ argument expects us to be.

In such a society, I suspect, we would have much less to fear from ‘slippery slope’ arguments.

Image courtesy of Pixabay.