A Primer on Slippery Slopes

Assume someone makes the following argument:

-All unhealthy activities are things that should be prohibited

-Smoking is an unhealthy activity

-Smoking is something that should be prohibited

The argument is valid, meaning its structure prevents the conclusion from being false if the premises are true. However, it is extremely vulnerable to a slippery slope rebuttal. Take the first premise, the major premise (the major premise is the one that shares the same predicate with the conclusion). The implications of the major premise are extraordinary. A legal system that took the major premise seriously would have to ban the overconsumption of liquor, the consumption of smokeless tobacco, sleepless nights, marathons, loud concert music, etc. Any argument with the same major premise would imply legal proscriptions for all unhealthy activities, just as the major premise indicates, not merely the activity as expressed by the subject of the minor premise (the one that shares the same subject with the conclusion), in this case, smoking. Consider this argument:

-All unhealthy activities are things that should be prohibited

-Eating fast food is an unhealthy activity

-Eating fast food is something that should be prohibited

If the major premise is subscribed to, then the above conclusion follows as well. But do we really desire a prohibition upon the consumption fast food? If one accepts the major premise as true, there is nothing one can do to mitigate its implications. If one wishes to prohibit smoking without prohibiting all other unhealthy activities, then one must adopt an alternative major premise.

So, the above argument is susceptible to a slippery slope counter argument and a slippery slope argument/counter argument is one that accuses another argument of containing a major premise that logically leads, if applied consistently, to unsatisfactory implications.

The trick to properly applying slippery slope arguments is to identify the major premise of a deductive argument that one suspects is vulnerable, assuming the argument is deductive (the vast majority of deductive arguments are syllogistic, so they will contain a major premise even if the arguer is unaware or denies it). If the major premise does not imply the disquieting consequences that the slippery slope argument alleges it does, then the slippery slope argument is no good.

Let's use an example of a slippery slope argument that I've become annoyed with. It is often said of arguments in favor of abortion rights that they imply, among other things, that people should retain the right to euthanize mentally challenged infants. Both are examples of human beings and the law allows for the killing of one. Why not the other as well?

This slippery slope argument would work if it was intended to criticize the following pro-abortion rights argument:

-Activities that involve humans killing other humans they deem as undesirable are activities that should be legal

-Abortions are activities that involve humans killing other humans they deem as undesirable

-Abortions are activities that should be legal

Consider a grim implication if one accepts the major premise above:

-Activities that involve humans killing other humans they deem as undesirable are activities that should be legal

-Murders are activities that involve humans killing other humans they deem as undesirable

-Murders are activities that should be legal

This, however, is an argument in favor of abortion rights that one will be hard pressed to discover. Now consider this alternative argument:

-All activities that involve human beings modifying their own bodies without resort to duress against others are activities that should be legal

-Abortions are activities that involve human beings modifying their own bodies without resort to duress against others

-Abortions are activities that should be legal

The major premise in this pro-abortion rights argument doesn't even approach sanctioning infant euthanasia, hence the aforementioned slippery slope argument from euthanasia fails to demonstrate that the major premise here yields a slippery slope.

Failing to demonstrate the presence of a slippery slope is not the only possible flaw of a slippery slope argument. Some successfully identify a slippery slope but then subsequently assign a false evaluation to the "slippery slope" in question. No doubt, it must have been argued at one time that compliance with the proposition

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the pursuit of Happiness"

should be adjusted due to the fact that, if taken literally, such a statement would imply that blacks would be worthy of legal rights sanctioning their exemption from slavery, laws mandating segregation, prohibitions against interracial marriage, etc. We can agree with a slaveowner's assertion that such a categorical interpretation of Jefferson's famous dictum would imply that slavery, segregation, and the whole array of laws aimed at repressing blacks should be annulled. However, what we must disagree with is his estimate of the logical implications and his classification of them as a "slippery slope".