On “Slippery Slopes”: A Response to Richard Mouw

On “Slippery Slopes”: A Response to Richard Mouw July 18, 2014

That’s the title of my latest essay over at The Catholic Thing. It is a response to a First Things blog post by Richard Mouw. Here’s how my piece begins:

My friend, Richard Mouw, a philosopher and former president of Fuller Theological Seminary, has raised an important challenge about the use of counterexamples when making one’s case on certain controversial moral and political questions.

He shares one of the arguments he employs to explain to his friends why he opposes the legal recognition of same-sex “marriage” (SSM): “If we are to operate as a society on the assumption that any sincerely held view about what constitutes a marriage should be granted status in our laws and practices, I have asked, what would keep us from legalizing plural marriages, or even incestuous ones?” Mouw says that his question is often “met with disdain,” with the retort, “[C]an’t you do better than a ‘slippery slope’ argument?”

He finds the retort frustrating, since, “some slopes are indeed slippery, and we do well to approach them with caution.” In other words, if you advance the truth of principle X in order to justify practice Y, something that you support, why not also accept practice Z, something that you reject, since it too is entailed by principle X?

So, for example, if you support the legalization of marijuana for competent adults on the principle that “one has a right to do whatever one wants to one’s body without directly harming others,” then that principle not only justifies marijuana legalization but also the decriminalization of hard drugs like heroin.

A person who resists this entailment by saying it’s a slippery-slope fallacy is confusing the fallacious form (often called a “causal slippery slope”) with the legitimate form of the slippery slope (often called a “logical slippery slope”). To point out that a principle entails something undesirable is not a slippery-slope fallacy. It’s an acknowledgment that principles have a logic of their own, so to speak.

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  • Donalbain

    But if you have an actual argument against polygamy, then use THAT argument when someone tries to advocate polygamy. If you have an actual argument against incestuous marriage, then use it when someone tries to advocate for incestuous marriage. If you say gay marriage is wrong because incest is wrong, then you are magnificently missing the point and you are showing that you have no actual reason that the rest of us should take seriously in the argument on the rights of gay people to marry.

    • hjill


      I think you have misunderstood. The arguments against polygamy and incestuous marriage are largely the same as those against SSM, and that is precisely the point. Those with whom he disagrees on SSM do not see that the logic of their position would necessitate as well these other forms of marriage, yet they maintain that these other forms should not be given the same legal status. Thus, they hold a logical contradiction.

      If, however, you believe we should legally equate polygamous, incestuous, homosexual, and heterosexual marriages, then you do not hold this contradiction and this line of reasoning does not apply to you.

      • Donalbain

        If the argument against SSM stood on its own, there would be no need to invoke polygamy. But the arguments I would use against polygamy are essentially pragmatic rather than moral so while I support SSM, I do not support (or oppose) polygamy.

        If your argument against X relies on the notion that you also oppose Y, then I contend your initial argument is weak.

  • The sad thing is that in many ways, gay marriage isn’t at the top of the slippery slope, but in the middle. It started with contraception, then pornography, then free love, then abortion….we’re quite a ways down the slope already, and I very much doubt we’re at the bottom yet.

    • I agree. Sin begets ever greater sin. It goes into deeply darker things the further we go down. At the bottom lies death.

      • Death of the soul, I hope you mean. Death of the body can come somewhat before the bottom. Along the way for those who don’t die, is enjoying the death of others.

        Don’t believe me? do a web search on “she asked me to kill her”. I refuse to link to any of those stories.

  • Zxenia Cvenka

    It seems to me that your argument about a slippery slope is a slippery slope. Gay marriage is OK. Most Catholics believe so.

    • Dagnabbit_42

      Zxenia Cvenka:

      The Catholics you describe as believing that “gay marriage is OK” are, usually, very ignorant of the Catholic faith.

      A person who actually knows the faith is aware that the truth of Catholicism entails, as a requirement, the infallibility of the ordinary Magisterium in matters of faith and morals preached to the universal Church. It’s one of the “Catholic distinctives”; one of the things which makes Catholicism be something different than Episcopalianism or Eastern Orthodoxy.

      And, a person who actually knows the faith is aware that one of the things the Magisterium has always taught as a matter of faith and morals preached to the universal Church, is the moral wrongness and intrinsic disorderedness of homosexual acts.

      Therefore — and there isn’t any wiggle room about this — if homosexual acts are, indeed, “OK,” then Catholicism is false. Conversely, if Catholicism is true, homosexual acts are, as the Catholic Magisterium infallibly teaches, disordered and mortally sinful. And in that case, obviously, “gay marriage” isn’t “OK.”

      Now one easy way to respond to your statement, “Most Catholics believe so” would be to simply point out that people who believe so, by definition, aren’t Catholic, because they don’t believe in Catholicism.

      But unfortunately I can’t do that, because there are various definitions of what makes a person “Catholic,” and only ONE such definition involves actually believing the Catholic faith. Others include being baptized a Catholic, or being subject to the proper jurisdiction of Catholic Canon Law, or self-describing as a Catholic. According to THOSE definitions, a person baptized a Catholic whose beliefs are not Catholic is not described as “not a Catholic” but just “a bad Catholic.”

      So to say that persons who firmly reject Catholicism aren’t “Catholic” falls afoul of certain definitions of “Catholic.” Still, what one can say is this: What they believe isn’t Catholicism.

      And yet I find that many such folks somehow THINK that they believe Catholicism. They’ve been taught it so badly, or taught something else in place of it, that they don’t know it well enough to recognize things which contradict it. It would be like being a Libertarian while simultaneously embracing the Marxist “from each according to his ability, to each according to his need” mantra. If you don’t know your own opinions well enough to tell when something contradicts them, can you really claim that they’re “your” opinions?

      Such folks also don’t seem to be aware that “most Catholics” believing something doesn’t make it Catholicism. They don’t seem to know Catholicsm well enough to realize that Catholicism, of all faiths, doesn’t work that way: The Catholic faith is what the Magisterium teaches.

      This isn’t the case for any other faith so far as I know. Take the Lutherans as an example. (They are a worthy and respectable group; I am not singling them out for any lack of respect; I could choose Anglicans or any other Christian group; or Muslims or Buddhists or whatever.) Over time, “Lutheranism” changed; but it wasn’t because Lutheranism had a group of bishops ordained in apostolic succession led by a successor of Peter who said it needed to change. Instead, various Lutherans disagreed with one another, calling various doctrines into question; and over time, the “center of gravity” of the whole crowd of Lutherans (clergy and laity) moved from where that center of gravity stood in the 1600’s or the 1700’s.

      So you see that the formula “most Lutherans” actually makes a difference to what Lutheranism IS. It has to do so, because Lutheranism is set up with only one authority; namely, people’s interpretations of the Bible. Since people’s interpretations can drift over time, so can the “official” Lutheran faith.

      But Catholicsm, because it has the Magisterium, by definition can only change when what the Magisterium teaches has changed.

      And because the Magisterium teaches that some of these teachings are infallible and permanently unreformable, it logically follows that THOSE teachings can never be reversed. To do so would prove Catholicism false. And no organization — even a normal human one! — is going to commit organizational suicide so spectacularly as that.

      To put it another way: The Catholic faith always has a required hermeneutic requirement called “The Hermeneutic of Continuity.” When interpreting any Magisterial teaching, one is obligated to interpret it in a fashion that doesn’t contradict an earlier Magisterial utterance on the same topic, but only expands or deepens it without contradiction. This is a requirement because, obviously, if the Magisterium ever “infallibly” contradicts an earlier “infallible” teaching, it disproves its own infallibility, and with it, Catholicism.

      Anyway, your post suggested a certain unfamiliarity with all of that. So I thought I should point it out.

      BTW, one other thing you should know about “Catholic” opinions on gay marriage, contraception, legalized abortion, remarriage after divorcing from a valid marriage, and so forth: The polls taken on such topics typically consider someone “Catholic” if they self-identify or were baptized Catholic and haven’t firmly embraced anything else later in life. Such polls therefore are considering the opinions of many folks who haven’t darkened the door of a church in decades.

      There are, however, polls which focus on a more realistically “Catholic” group of persons: Those who attend Mass every weekend except when ill, and who go to Confession once a month or more. Poll THOSE folks, and you find that there are majorities (barely so, in the case of contraception, but Rome wasn’t burned in a day and the post-1960’s failure of Catechesis was most profound in that area) in agreeing with the Magisterium on these teachings.

      Anyway, that’s worth keeping in mind when considering what most “Catholics” believe. There are catholics and then there are Catholics, so to speak.

  • I am curious about whether the marijuana example can be applied to smoking too. It will look like this:

    So, for example, if you support the legalization of smoking for
    competent adults on the principle that “one has a right to do whatever
    one wants to one’s body without directly harming others,” then that
    principle not only justifies smoking legalization but also the
    decriminalization of marijuana (and mutatis mutandis) hard drugs like heroin.

  • LionelAndrades

    Dominus Iesus, Redemptoris Missio carry the Cardinal Francesco Marchetti Selvaggiani mistake