Zac Alstin asks a perfectly reasonable question

Aside from the fact that people who constantly place us on slippery slopes loudly shout that, “Slippery slope arguments are fallacies!” what actual reason do we have for believing the slippery slope arguments are fallacies? I think slippery slope arguments–proven right again and again by our experience of the culture of death–are just another way of saying “Ideas have consequences”. So does Zac Alstin. The next time somebody barks at you that slippery slope arguments are fallacious, ask why they have such a nasty tendency to come true.

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  • Robert King

    The “slippery slope” is a fallacy only in evaluating the form of a logical syllogism. It says that a “slippery slope” argument does not lead to a necessary and inevitable conclusion. It regards how certain we can be of the conclusion, not whether or not the argument is true.

    It is not a “slippery slope” argument to note that there is no further obstacle to something. This is what many note by saying that the same justification for “same-sex marriage” can be applied, without significant alteration, to justifying polygamy or other forms of “marriage” that we currently consider perverted.

    It is a “slippery slope” fallacy to say that polygamy necessarily and inevitably will result from legalizing “same-sex marriage”.

    But it is valid to say that accepting the justification for “same-sex marriage” makes accepting the same justification for polygamy much more likely. This is an argument for probability, not necessity.

    Moreover, if an argument is used to justify one thing (say, “same-sex marriage”), but not another (say, polygamy), then the burden of showing the difference between those things rests on the one arguing to justify one but not the other.

    In short, a “slippery slope” is not a good way to draw a conclusion; but it is an excellent way to raise a question.

  • Thinkling

    I have not read Alston’s piece yet, but I think Robert nailed it above. The criticism of the slippery slope argument is essentially that it is not deductive. This is true, but in can be immensely inductive.

  • jcb

    Slippery slope arguments get classed as inductive fallacies. The allegation is not simply that they’re inductive arguments (which is no allegation at all) but that they’re bad inductive arguments.

    That being said, I think the fallacy is entirely imaginary. There’s no unique pattern of bad reasoning there. (I’m suspicious of informal fallacies in general, and think that giving students a list of informal fallacies obscures the actual problem in reasoning and inclines them to reflexively shout “FALLACY!” whenever they hear certain words in arguments, rather than actually analyze the argument’s structure.)

    When people make arguments of the sort that cause others to shout “SLIPPERY SLOPE!” as if they were a cat that’s heard the can opener, the people making the arguments are doing one of two thing:

    i) They’re arguing that some policy will lead to bad consequences, and thus ought not be pursued. “Allowing gay marriage will lead to allowing polygamy. So, (1) if we don’t want to allow polygamy, we shouldn’t allow gay marriage. (2) We don’t want to allow polygamy. So, (3) we shouldn’t allow gay marriage.”

    This is a formally valid argument — (3) follows by modus ponens from (1) and (2). It can’t be fallacious. It might have a false premise, but that doesn’t make the argument fallacious. It simply makes it unsound.

    ii) Or, they’re arguing that the principles that license one policy also license another. (The issue here is one of intellectual consistency, not of likely consequences in the real world.) “The principles by which people argue for gay marriage also license polygamy. So if those principle are true, then polygamy is permissible. But polygamy is not permissible, so those principles are false.”

    Again, perfectly valid deductive argument — modus tollens. No fallacy here. Attacking the argument requires attacking the premises, not simply shouting “SLIPPERY SLOPE!”

    (This is my general complaint about the informal fallacies — I think that in all cases it’s more illuminating and helpful to recast the arguments as formally valid arguments and then focus on whether the premises of those arguments are true. Doing that keeps you from doing silly things like declaring all arguments that hold that a policy ought not be pursued because it might have bad consequences, or that a principle is false because it entails that we should do something that we shouldn’t do, are fallacious.)

  • Telemachus

    I wonder though…

    A “slippery slope” argument may not be purely deductive in isolation, but if you add to it an assumption that peoples’ motivations remain the same, you might be able to make (if not a perfectly conclusive deduction) a conclusion which is simply too probable not to be taken seriously.

    I might make a distinction, therefore, between a “necessary conclusion” and an “effective conclusion.” To derive this so-called “effective conclusion,” two criteria must be met:

    (1) The logic arguing for X must be shown to be applicable to arguing for Y.
    (2) One must analyze the beliefs, intentions, etc. of those arguing X, and show that these beliefs, intentions, etc. are positively disposed to Y.

    I’m no philosopher, so this might be easily rebutted. I’m not a believer in pure logic either, however, because human action is not purely logical.

    God bless,

  • Telemachus

    Oh, wanted to add: just like the “slippery slope is a fallacy” argument, I think David Hume’s “can’t derive an ought from an is” is also not a valid catch-all for dismissing moral argumentation.

    Why can’t I derive an ought from an is? Because Hume said so? Such a statement effectively asserts that there is no such thing as natural law or teleology, doesn’t it? Unacceptable, at least for the Catholic. We believe in a rationally ordered creation which has limits and purposes.

    God bless,

  • Anonsters

    Well. You asked. I give you Eugene Volokh’s .

    • Anonsters

      Er. The above is a link to SSRN to his paper “Mechanisms of the Slippery Slope.” Click on the period to proceed. Ahem.