The slippery slope argument is another name for the argument of gradualism and direction. It consists in saying that such a controversial action, A, apparently convincingly backed by such and such arguments, should not be accepted, even if it might seem reasonable, because, if it were, the same principles and reasoning could be used to argue in favor of another action of the same kind A+, which is much more controversial, and then for another action A++, that one would find quite unacceptable. In effect, accepting A removes all possible limit, “when started, you cannot stop”. The slippery slope counter-argument is based on the precautionary principle, aimed at preventing a risk of extension of the decision adopted.

In a debate about the legalization of drugs, a participant proposes to legalize hashish:

AC. — [Legalization, or rather domestication] will not eliminate the problem of drugs. But it is a more rational solution, which will eliminate the mafias, reduce delinquency, and also reduce all the fantasies that feed drug taking itself and are part of drug marketing.

The opponent counters this pragmatic argument with a slippery slope argument,

If you legalize hashish, you will have to legalize cocaine, then heroine, then crack and cocaine, and all the worst dirty things that man can find.
Le Nouvel Observateur [The New Observer][1], 12-18 Oct. 1989

For a refutation of the same position based on its perverse consequences, S. Pragmatic Argument; for a refutation based on the very wording and definition of the project, S. Related Words.

This argument is based on the following operations. The question is:

Question: — What should we do about the issue of drugs?
S1 — We should legalize hashish, for such and such reasons.

The opponent S2 is reluctant to accept this proposal, even if the reasons presented by S1 are not entirely unacceptable. S2, however, refuses to become involved in S1’s process of reasoning on the basis of the following analysis of the situation.

(i) Consider the broader graded category including the object concerned, S. Categorization; Classification:

The category “drug” covers hashish, heroin, crack cocaine and so on.
Heroin is worse than hashish, and crack cocaine is worse than heroin

So, hashish is the low point, the weak point by which one enters the graded category of drugs.

(ii) An evaluation
The decision to legalize hashish may be debatable, but the legalization of heroin would clearly be unacceptable, and the legalization of crack cocaine would be unthinkable, even outrageous. This gradation mirrors gradation (i).

(iii) A driving mechanism
The decision to legalize hashish is related to those to be made in relation to heroin and crack cocaine; the same question will inevitably arise about these harder drugs:

Should heroin be legalized? Should we legalize crack cocaine?

Legalizing hashish would set a precedent; the same arguments justifying the legalization of hashish (“eliminate the mafias, reduce delinquency, and also reduce all the fantasies about drug taking”) may well be used to legalize heroin, and even crack cocaine. Given the success of these arguments to justify the legalization of hashish, it would be near impossible to dismiss these arguments if they were to be used to justify the legalization of heroin and crack cocaine. A precedent has been set. In short, by accepting A, one has taken a decisive step toward accepting A+ and A++.

(iv) Conclusion: Let’s reject the legalization of hashish

The structure of the slippery slope argument parallels that of the argument from waste:

Slippery slope: Don’t get started, you won’t be able to stop!
Argument from waste: Since you started, you must go on!

The gradualist strategy and the slippery slope argument consider a hierarchized class of elements, S. Gradualism. The question is whether the status of these elements should be changed? The Gradualist is in favor of a change of status, and engages in a step-by-step, progressive modification of the existing hierarchy. The opponent considers that the status of the top elements can in no way be altered, and will use a slippery slope argument to counter the gradualist by opposing any change, however slight, in the status of the lower element.

The driving mechanisms invoked (often implicitly) on stage 4 can be very different:
— Psychological:“he who steals an egg will steal an ox”.
— Organic, causal: The slippery slope designation is metaphorical, and clearly illustrates the physical movement of an ever faster physical fall. One could also evoke a domino effect, where the first falling domino pushes the second, the significance of each falling domino becoming greater and greater.
— Strategic: The key point is the attribution of bad intentions to the proponent. The opponent may consider (as in our example) that the proponent is well intentioned, and that his or her public goal is indeed the authentic goal, and that he or she does not see the potential extreme consequence in which this might result. In this case, the proponent is portrayed as a naive or idealistic arguer, who doesn’t see the consequences of what he or she is promoting, but nevertheless maintains his or her moral integrity. This development reflects Hedge’s recommendation, not to attribute to the adversary hidden and manipulative intentions (sixth rule for honorable controversy, S. Rules). Nonetheless, maybe with a polemical intent, the proponent might be framed as a Machiavellian character with the active intention of developing a gradualist strategy, with the manipulative intention of implementing step-by-step, the most extreme measure beginning with the relatively benign one; hashish would be the bait initiating a priming strategy. So, the opponent will cast upon the proponent a suspicion of private, ugly intentions, S. Motives and Reasons.

[1] Le Nouvel Observateur is a French weekly political and cultural newspaper.