Slippery Slope, Same Sex Marriage, Goats & Corpses

Gray-GoatWhile same-sex marriage seems to have momentum in its favor in the United States, there is still considerable opposition to its acceptance. This opposition is well stocked up with stock arguments against this practice. One of these is the slippery slope argument: if same-sex marriage is allowed, then people will then be allowed to marry turtles, dolphins, trees, cats, corpses or iPads.  Since this would be bad/absurd, same-sex marriage should not be allowed. This is, of course, the classic slippery slope fallacy.

This is a fallacy in which a person asserts that some event must inevitably follow from another without any argument for the inevitability of the event in question. In most cases, there are a series of steps or gradations between one event and the one in question and no reason is given as to why the intervening steps or gradations will simply be bypassed. This “argument” has the following form:

1. Event X has occurred (or will or might occur).
2. Therefore event Y will inevitably happen.

This sort of “reasoning” is fallacious because there is no reason to believe that one event must inevitably follow from another without adequate evidence for such a claim. This is especially clear in cases in which there are a significant number of steps or gradations between one event and another.

In the case of same-sex marriage the folks who claim these dire results do not make the causal link needed to infer, for example, that allowing same-sex marriage will lead to people marrying goats.  As such, they are committing this fallacy and inviting others to join them in their error.

While I have written a reply to this fallacious argument before, hearing someone making the argument using goat marriage and corpse marriage got me thinking about the matter once again.

Using goat marriage as an example, the idea is that if same-sex marriage is allowed, then there is no way to stop the slide into people marrying goats. Presumably people marrying goats would be bad, so this should be avoided. In the case of corpse marriage, the gist is that if same-sex marriage is allowed, then there would be no way to stop the slide into people marry corpses. This would presumably be bad and hence must be avoided.

The slide down the slippery slope, it must be assumed, would occur because a principled distinction cannot be drawn between humans and goats. Nor can a principled distinction be drawn between living humans and corpses. After all, if such principled distinctions could be drawn, then the slide from same-sex marriage to goat marriage and corpse marriage could be stopped in a principled way, thus allowing same-sex marriage without the alleged dire consequences.

For the slippery slope arguments to work, there must not be a way to stop the slide. That is, there is a smooth and well-lubricated transition between humans and goats and between living humans and corpses. Since this is a conceptual matter rather than a matter of actual slopes, the slide would go both ways. That is, if we do not have an adequate wall between goats and humans, then the wall can be jumped from either direction. Likewise for corpses.

So, for the sake of argument, let it be supposed that there are not such adequate walls—that once we start moving, we are over the walls or down the slopes. This would, apparently, show that same-sex marriage would lead to goat marriage and corpse marriage. Of course, it would also show that different sex-marriage would lead to a slide into goat marriage and corpse marriage (I argued this point in my book, For Better or Worse Reasoning, so I will not repeat the argument here).

Somewhat more interestingly, the supposition of a low wall (or slippery slope) between humans and animals would also lead to some interesting results. For example, if we allow animals to be hunted and there is no solid wall between humans and animals in terms of laws and practices, then that would put us on the slippery slope to the hunting of humans. So, by the logic of the slippery slope, we should not allow humans to hunt animals. Ditto for eating animals—after all, if same-sex marriage leads to goat marriage, then eating beef must surely lead to cannibalism.

In the case of the low wall (or slippery slope) between corpses and humans, then there would also be some odd results. For example, if we allow corpses to be buried or cremated and there is no solid wall between the living and the dead, then this would put us on the slippery slope to burying or cremating the living. So, by the logic of the slippery slope, we should not allow corpses to be buried or cremated. Ditto for denying the dead the right to vote. After all, if allowing same-sex marriage would warrant necrophilia, then denying corpses the vote would warrant denying the living the right to vote.

Obviously, people will want to say that we can clearly distinguish between animals and humans as well as between the living and corpses. However, if we can do this, then the slippery slope argument against same-sex marriage would lose its slip.

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  1. Service animals started out as a few seeing eye dogs but now, in most states,
    Any animal can be declared a device animal– and apartment houses and condos are required, by law,to accept them. Dogs, cats , reptiles and even miniature horses must be allowed.
    That’s a slippery slope that became an avalanche.

  2. Your two step argument is over-simplified to express the fault with the slippery slope fallacy. You haven’t shown what it is about the connection between (1) and (2) that makes it the slippery slope argument. Your two statements could be part of a modus ponens argument, in which case Y will follow from X. And of course many other fallacies fit this pattern. You’ve essentially provided one premise and the conclusion from any number of valid or invalid arguments.

    This is how the slippery slope argument is better presented:

    1. Event X occurs when we introduce process P, to situation x.
    2. Therefore event Y will occur if we introduce process P, to situation y.

    The fallacy has two significant errors:

    A) It is possible that there is no reason to suppose we will or should apply P to situation y just because we choose to apply it to situation x. In fact it may be that Y (bad) might follow from applying P to y may be good enough reason not to apply P to y, even though we choose apply P to x in order to cause X (good).

    B) The argument also has to show that applying P to y would result in Y, which it does not necessarily – though it may be obvious that it would be so in some specific cases.

    So, that legalising same sex marriage [legalising marriage (P) for same sex relationships (x) results in same sex marriage (X)]is a good idea does not lead us to conclude that legalising inter-species marriage would be a good idea too [legalising marriage (P) for same inter-species relationships (y) results in inter-species marriage (Y)]. In this case it probably is the case (i.e it’s pretty obvious) that legalising inter-species marriage would result in some inter-species marriage; but if we decide that inter-species marriage is not good then we need not allow it.

    “So, for the sake of argument, let it be supposed that there are not such adequate walls” – While you play devil’s advocate with this I agree with your points. But the very notion that we should even consider this notion of inadequate walls is plain silly, as your later examples point out.

    Now, exactly why can’t I marry that lovely sheep I’ve had my eye on?

  3. Good article, I’m directing my students to read it as they are getting into logical fallacies. One potential problem I’ve often had with the slippery slope fallacy is that it often seems difficult to confirm until after the fact. That is, sometimes events do snowball into undesired consequences. For example, some of the early Nazi Germany euthanasia programs (the T-4 programs?) targeting children with mental or physical disabilities leading to similar applications to adults leading to similar applications to people “guilty” of political crimes, sexual orientation, racial identification, etc. Do you have any thoughts or suggestions on how we identify “legitimate” slippery slope fallacies from legitimate concerns that one course of action will lead to negative consequences?

  4. Michael,

    As above, here is how I see the the slippery slope as a fallacy:

    1. Event X occurs when we introduce process P, to situation x.
    2. Therefore event Y will occur if we introduce process P, to situation y.

    Whereas a legitimate slippery slope argument would be:

    1. Event X occurs when we introduce process P, to situation x.
    2. Applying P to x will cause (directly or indirectly) P to be applied to y, because (some sub-argument’s conclusion)
    3. Therefore event Y will occur if we introduce process P to x because that will cause P to be applied to y, when we know that applying P to y will cause Y.


    1. Moderate X religion will result of we apply faith P to moderate beliefs x.
    2. Applying faith P to x will cause P to be applied to extremist fundamentalism y, because (faith sidesteps reason and evidence and excuses any belief, so any believer will use it once they have experienced its efficacy in supporting their beliefs in the face of counter reason and evidence).
    3. Therefore extremist terrorism, bigotry, barbarism Y in the name of religious belief y will occur by the introduction of faith P to beliefs y.

    In this example we know applying P to y will and does cause Y – not with certainty and not in all cases, but with observed frequency due to observed examples throughout history.

  5. Doris Wrench Eisler

    Is is pretty sad to see an argument attempted where no real distinction is made between the marriage of two people of the same sex and a human being and an animal (or, corpse!)
    However if someone really wants to marry their Doberman, and the Doberman has no real objection, I would be inclined to let them go ahead.

  6. Hmm. I think the Argument from Goats (so to speak) is really a reductio ad absurdum, not a slippery slope argument. Nobody’s predicting that after legalizing same-sex marriage, we’ll actually find ourselves legalizing marriage to goats. There are lots of cultural reasons we will never do that. The better stated argument is a reductio–it says the reasoning involved in the defense of gay marriage would also yield a defense of marrying goats. So, the reasoning must be flawed.

    This reductio isn’t such a bad argument against certain kinds of defense of gay marriage. If your defense is simply that people should be free to have whatever relationships they like, then the reasoning does lead to approval of both same-sex and different-species marriages. Moral of the story (I think): advocates of same sex marriage shouldn’t make that very primitive argument! There are certainly much better ways to defend gay marriage.

  7. Oddly enough, if you drop by my blog you will see people arguing that allowing same-sex marriage will lead to goat marriage. But, I would agree that rational foes of same-sex marriage would use it as a reductio rather than to claim that we will actually get around to goat marriage.

    I do agree that the arguments involving the claim that people should be allowed to have any relationship they want are easy to crush. After all, this would entail that people could marry anyone or anything (even without consent) and that would be crazy. Though, of course, most of it has actually been done at one time or another.

  8. Can forbidding same-sex marriages be based on any strict logical argument?

    It is well known that some humans are born with biological characteristics that make their sex unclear. Some humans feel that they have one sex, but are “captured” in a body of the other sex. Some humans have – through treatment and operations – taken on the external appearance of the other sex. It is therefore impossible to classify all humans unambiguously into the categories “male” and “female”.

    These categories are therefore not intrinsic properties of the individual, but administrative labels. It is possible – and it happens – for one individual to be labelled with different sex in different administrative systems.

    If a marriage is defined as a union between two humans, the fuzzy boundary between “male” and “female” makes it logically impossible to define strictly the notions of “same-sex” and “different-sex” marriages.

  9. Eric Ferguson,

    Yes, logical arguments could be made against same-sex marriage. That is, the reasoning could be good. For example, if allowing same-sex marriage caused terrible harms, then it would seem to make sense that it should not be allowed. However, the weak point in the harm arguments is not the logic but the premises. That is, same-sex marriage does not seem to inflict any harms.

  10. Mirannabel Love

    I want to marry my same-sex cat! There is no sex involved, or desire for sex…I am just that crazy in love with her soul. We are both spayed – will that help?

    And what about marriage with goat corpses? Has anyone considered that?? (Oh wait, consider it AFTER I get permission to marry my cat please!)

  11. Mirannabel,

    Is it by mutual consent, with your cat? Is your cat able to give consent in a way that is meaningful – say, more so than a human minor of 15, and as well as a same-sex human adult? Does your cat demand this equality for self-determination that same sex human adults do?

    It doesn’t sound consensual with your dead goat though.

    I don’t think the slope is that slippery.

  12. Mirannabel Love,

    Cats cannot consent nor can goats (live or dead). So, marriage would not be possible. Sure, laws could be passed allowing it-but they would be morally wrong.

  13. Mirannabel Love

    Ron and Mike,
    You are right that a dead goat cannot consent, so marriage to one would be very wrong. I guess the dead goat owner will just have to eat it and then make some fantastic drum heads out of the hides instead – so much better for the goat that way!

    My cat is crazy about me – it is mutual. She also recognizes that her human is pretty nutty (even for the already nutty species called humans!) but she lovingly indulges me. When I tell her we are going to “get married a hundred times a day everyday forever” she purrs and snuggles and kisses me. You must understand – the more your human is crazy about you, the more treats and toys and pampered you get. She is no fool! LOL It’s GREAT to have your human so hopelessly in love with you!

  14. Mirannabel,

    Of course consent is only meaningful if one has the sane enough to have the mental capacity to give consent. That applies to humans as well as animals. Just sayin’ :)

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