Both causal and logical slippery slope considerations are legitimate when constructed properly, and both play a critical role in providing clarity on weighty moral issues.

Slippery slope arguments are a form of reasoning that links one way of thinking to an unintended consequence that’s likely to follow. With moral issues, if a behavior seems justified but “slips down the slope” in some way to something more drastic, it calls into question the morality of the initial behavior.

Some such appeals are faulty, of course, but some are valid. I want you to know the difference since you’ll likely encounter them. If you claim, for example, that doctor-assisted suicide will lead to involuntary euthanasia or that abortion liberty will lead to infanticide, you’ll likely be dismissed with, “That’s just the old slippery slope fallacy.”

Slippery slope concerns, however, are legitimate factors when thinking through the consequences of moral practices. There are fallacies of this sort, of course, since some acceptable practices don’t lead to extremes. Some do, though, simply by the force of the moral equation built into the issue. Those are the ones to be concerned about.

There are actually two distinct kinds of slippery slope appeals: a causal slippery slope and a logical slippery slope. The nature of each often becomes obvious after looking closely at the underlying circumstances related to the actions in question.

With a causal slippery slope, if some action thought to be morally acceptable leads to a result that’s morally questionable, it casts a shadow on the initial action. Simply put, if some consequence B is wrong, and permitting A will cause B to occur, then A is wrong, too.

Driving fast isn’t intrinsically immoral, but because it’s dangerous and leads to human harm, the wrong of the effect “slips over” into the cause, making it wrong, too. Some think pornography is acceptable, yet if it can be shown to cause violence against women, then pornography becomes morally suspect for that reason.

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