123. Effetto Domino

Slippery Slope Arguments

Il seguente brano è di particolare interesse anche per quanto riguarda il tema "eccezioni alla regola": quando e perchè.

(by  Douglas Walton, Professor of Philosophy at the University of Winnipeg)

“A slippery Slope argument gets started when you are led to acknowledge that a difference between two things is not really significant. Once having acknowledged this first step, it may be difficult to deny that the same difference between the second thing and some other third things is likewise not really significant. Once this sort of argument gets started, it can be too late to decisively stop it. You’re on the slippery slope. It can be applied over and over, driving you to concede a conclusion that is absurd.


A man is clocked at fifty-six miles per hour by a radar detection unit of the highway patrol in a fifty-five mile per hour speed limit zone. He argues to the patrolman that he should not get a ticket because the difference of one mile per hour in speed is insignificant. “after all it’s really arbitrary that the agreed-upon speed limit is fifty-five rather than fifty-six isn’t it? It’s just because fify-five is a round number that it is chosen as the limit”

What happens if the police officer accepts this arguments? Then the next speeder, who is clocked at fifty-seven miles per hour, will argue “Well, you let Smith off when he was clocked at fifty-six miles per hour. You conceded that one mile per hour doesn’t really make a significant difference. By the same criterion, you must let me off without a ticket as well (…) for the next motorist who is clocked off at fifty-eight miles an hour can use the same argument over again (…) Ultimately the poor officer will have to let any go without a ticket, no matter how fast he was going (…) Once the world spread, everyone can demand ‘equal treatment’ (…)  How should the traffic patrolman have critically replied to the first speeder’s argument? He could have replied that although the speed limit of fifty-five might be arbitrary to some degree, that is the exact limit set as uniform policy. And that uniform policy must be applied equally and fairly to all motorists. If a motorist is speeding to the hospital to save a badly injured passenger, then that could be fairly judged a significant difference to exempt this driver from the policy in a particular case. So there may be EXCEPTIONS in exceptional cases (…) We also require that rules should not be rigidly applied by a thoughtless bureaucracy. If an exception is reasonably judged to be a relevantly different enough case to fairly qualify as an exceptional case, then we require that the rule should be broken.

The domino effect argument  is the counteractive use of the possibility or threat of a slippery slope argument to counsel against taking a first step. It is often used as a conservative argument against any new policy or proposal is untried. For example, it might be argued that if terminally ill patients are allowed to refuse heroic medical treatment, this might lead to elimination of unfit. And this then eventually might lead to concentration camps and Nazi genocide squads. The domino effect is not a positive use of the slippery slope argument, but is a kind of defensive argument tactic or critical reply against a potential slippery slope that might develop. When dealing with the domino argument it is important to distinguish between the claim that certain consequences MIGHT develop and the claim that they WILL develop. The suggestion. The suggestion that they might develop is often used as a scare tactic, or strategy of intimidation to try to silence the opposition and prematurely close off the argument (…) The domino effect argument, for example, is often based on the premise that there is a causal link between So and S1, and between S1 and S2, and so forth until some ‘horrible’ outcome S12 is reached (…) Where the causal domino effect becomes a fallacy is in the context where the premise that each step  m i g h t  cause the next step is used to frighten an arguer to conclude that the last ‘horrible’ step  w i l l  happen unless he refuses do do anything that might cause the first step to happen. This type of argument can be criticized as inadequate if not enough additional proof of evidence is given to show that what might happen really will happen, or is likely to happen. Whether a causal type of domino effect argument is reasonable or not depends on the strength or plausibility of the evidence given to support the causal linkages proposed at each step. The classical case of the domino effect argument was its use during the Vietnam War era to argue that if Vietnam fell to the Communists the neighboring countries like Cambodia would also fall. Then other adjacent countries would fall until the whole of east Asia would be in Communists hands. This argument was often used as a kind of scare tactic by its exponents, and because not much evidence seemed available to back it up very firmly, it came to be thought of as a fallacious type of argument, in this particular instance (…)