Thursday, March 28, 2013

The fallacious slippery slope

I find that the best way to talk about fallacies and biases is to wait for a good example to come around.  Recent discussion of same-sex marriage offers some excellent examples of slippery slope arguments.  Chris Hallquist recently highlighted an example:
By turning marriage into a socially constructed reality that doesn’t have a nature, marriage can then be whatever you want it to be. Not just the union of a man and another man, but also even two men and a woman–three partners in marriage. Or it could be a man and a child. Or maybe even a man and his dog, if he feels close enough to his pet to want to marry it.

--William Lane Craig
(In context, William Lane Craig is arguing that long-term relationships are so uncommon among gay men, that they couldn't really be fighting for marriage for its own sake.  Instead, their real goal must be to "deconstruct marriage".  But I will ignore this context to focus on the slippery slope only.)

I remember learning about logical fallacies in grade school English, and they would always include the "slippery slope fallacy" among others.  I think this is wrong.  A slippery slope argument is not necessarily fallacious.  It depends on how it's used.  Therefore, I call this a fallacious slippery slope argument to distinguish from those slippery slope arguments which are not fallacious.

First, I wish to divide slippery slope arguments into two categories (which are my own creation):

1. The slippery slope of reasoning
2. The slippery slope of consequences

Example of a slippery slope of reasoning: Suppose I claimed that all the best things are green.  You could counter, "But if you follow that slippery slope, you must also believe that cats (which are not green) are not among the best things!  Clearly this is absurd."

Another example: "If you believe that same-sex marriage should be legal, then you should also believe that man-dog marriage should be legal.  This is clearly absurd."

This kind of slippery slope argument is no different from an argument ad absurdum.  In a mathematical argument, we'd call it proof by contradiction.  It's a logically valid argument, it's just that it's often unsound (ie the conclusions follow from the premises, it's just that the premises are wrong).  In the green example, the person forgot to show that it is absurd to believe that cats are not the best things.  In the example of same-sex marriage, the person forgot to show that if same-sex marriage is legal, then man-dog marriage should be legal.  But if we granted the premises, the conclusions would follow.

William Lane Craig uses a slippery slope of consequences.  He does not say that if we support same-sex marriage, we must logically also support man-dog marriage.  Rather, he says that if same-sex marriage is legal, this would lead people to also legalize man-dog marriage in the future.  The argument is not about what people should conclude from prior beliefs, it's about what people will do, how people will behave.

It's basically a moral argument.  Lane Craig doesn't want people to marry dogs, so from his perspective it's worth taking actions to avoid this.

But there's something rather strange about this argument.  We are free agents.  We can either choose to allow man-dog marriage or not.  We will choose according to our preferences.  If we prefer to allow man-dog marriage, why should we prevent getting what we prefer?  If we prefer not to allow man-dog marriage, then why would we choose to allow man-dog marriage?

Mind you, the slippery slope of consequences still isn't necessarily fallacious.  There are some situations where we might worry that our future selves will be irrational.  Or that other people will be irrational.  Or that we'll have different preferences in the future.  And there are game-theoretic situations where it's better to have fewer options (I've recently been reading about decision theory).

But none of those situations are relevant here.  Making laws is a very deliberative process, not something that's decided on the spot on an irrational whim.  And it's hard to imagine a non-trivial game-theoretic situation.  Usually there are people who want a law, and people who don't, and that's that.

So despite the slippery slope argument being an acceptable argument in general, William Lane Craig manages to use a form that is completely fallacious.


On a related note, my boyfriend pointed out a slippery slope argument made by Supreme Court Justice Scalia, when he argued in favor of anti-sodomy laws in 2003:
"Today’s opinion dismantles the structure of constitutional law that has permitted a distinction to be made between heterosexual and homosexual unions, insofar as formal recognition in marriage is concerned. If moral disapprobation of homosexual conduct is 'no legitimate state interest' for purposes of proscribing that conduct; and if, as the Court coos (casting aside all pretense of neutrality), '[w]hen sexuality finds overt expression in intimate conduct with another person, the conduct can be but one element in a personal bond that is more enduring,' what justification could there possibly be for denying the benefits of marriage to homosexual couples exercising '[t]he liberty protected by the Constitution'?"

-Lawrence v. Texas, 539 U.S. 558, 605-06 (2003) (Scalia, J., dissenting) (internal citations omitted).
I'm sure by now Scalia has thought of a few justifications for denying same-sex marriage that do not rely on anti-sodomy laws.


Anonymous said...

I think you misunderstand Craig's point. He is not only taking a moral angle, he is saying it logically follows from saying marriage is something defined by humans that marriage can be anything we define it as. He would argue that marriage in itself is not a social construct but a real thing with a certain nature. The slippery slope that he would be arguing for is a direct result of making 'marriage' merely a social construct. The result would follow that we could alter the definition as much as we wanted to make it include anything, from a union between a man and a woman to a union between a brother and a sister, or a man and a dog. Whether or not a man marrying a dog is moral would be a second point which he could then address. But do note this - his argument is not that allowing same-sex couples to marry would lead to allowing a person and a dog to marry. He is arguing that if marriage becomes a socially defined term, then it could be defined as the union between a man and a dog just as easily as it could be defined as the union between a man and a man.

You may reject the notion that there is a "nature of marriage," but that is the concept his argument rests on. Denying it would be to say that he is correct that marriage could be anything we define it to be.
He would then go on to argue why it is, in fact, wrong to allow two siblings or species to marry. But this is not the crux of the argument.

miller said...

So you're saying that WLC is using a slippery slope of reasoning?

If so, then he needs to demonstrate that man-dog marriage is not merely morally absurd, but that it is logically absurd. He's just making it harder on himself that way. I can think of many arguments why man-dog marriage might be morally wrong, but I can't imagine why it's logically impossible.

Anonymous said...

Sorry it has taken me so long to get back to this post. Yes, I am arguing that Craig is not using the slippery slope of consequences, but of reasoning, following the (useful) distinction you have made. My point was that you may be mistaken when you claim:

"He does not say that if we support same-sex marriage, we must logically also support man-dog marriage. Rather, he says that if same-sex marriage is legal, this would lead people to also legalize man-dog marriage in the future."

As stated in my previous post, it is a logical consequence of saying man defines marriage (rather than marriage having a nature) that marriage can be anything we define it as. You actually prove his point when you say you can't imagine why it is logically impossible for man-dog marriage. Craig would agree that once you strip away the idea of marriage having a nature, it is a slippery slope of reason, not of consequences (to employ your distinction), which would lead to man-dog marriage. When marriage ceases having a nature, it can be anything at all! Whether humans consequential choose to define it as being between man and dog is beside the point; Craig's point is that it would logically follow. I contend that this is not a fallacious use of the slippery slope argument.

miller said...

So it sounds like you're saying that WLC's position is that it is in fact absurd to believe that man-dog marriage is logically possible.

If that is true, then you're right: it is not an example of a fallacious slippery slope. It's merely unsound, since he now has to prove the premise that man-dog marriage is logically impossible.

Although, how do you know that this is Craig's position? Do you have a citation?

Anonymous said...

This will probably be my final comment here, as it seems we are beginning to go in circles. Perhaps I am unclear about what is meant by "a slippery slope of reasoning." My point is simply that, yes, Craig is arguing that if we accept homosexual marriage, we must also logically accept man-dog marriage. He does not seem to be saying the existence of man-dog marriage is logically absurd, and I'm not sure why he would have to be saying that. The logical absurdity (according to Craig's premise that marriage has a nature) would be to allow homosexual marriage while not allowing man-dog marriage, assuming the justification for homosexual marriage is that "marriage is a social construct."

I have no sources for my argument other than Craig's own words, which you posted. However, I don't think I am having to read anything extra into the text to make these points.

miller said...

Yeah, actually now that I'm looking at this again, I'm seeing your point. I think a more elaborate classification of slippery slope arguments may be necessary.

A slippery slope argument consists of two steps:
1. A leads to B.
2. B is absurd or bad.

A and B could refer to truth-statements, ethical statements, or policy choices.

Step 1 could go in one of two ways:
1a. There are arguments that if A is true/good, then B is also true/good.
1b. If we adopt policy A (or believe statement A), this will lead to consequences B.

Step 2 can also go in two ways:
2a. B is absurd in the logical sense.
2b. B is wrong in the ethical or moral sense.

WLC seems to be using steps 1a and 2b. This resulted in confusion between us as to whether the slippery slope argument was logical or moral in character. It's both.

I think I agree that the 1a/2b form is not necessarily fallacious. We usually want our ethical rules to be logically consistent.

Larry Hamelin said...

There are three problems. First, the requirement that all parties to a marriage must be actual human beings is not challenged by same-sex marriage. Man/dog marriage is thus not entailed.

Second, we have to accept the premise that man/dog marriages are in some sense morally bad. Why do I care if people marry their dogs (so long as marriage does not confer human status)?

Third, we already stepped on the slippery slope when we decided that incarcerated infertile atheists and heathens had a constitutional right to marry (and they do).

miller said...

Oh yes, there are definitely still problems, but these problems are in the "unsupported assertions" territory, rather than the "fallacy" territory. Possibly relevant: my fallacy diagram

Anonymous said...

Hey, I think you nailed it with your 1a/2b distinction. This seems to me to be Craig's argument. And as you pointed out, whether or not consequence B is wrong in the moral sense would have to be addressed separately (which requires additional assertions). BTW, giving myself a name here, but I was the Anonymous poster.

B9 said...

Whoops, accidentally went Anonymous again in last comment...

Larry Hamelin said...

I think the slippery slope fallacy is just a special case of the equivocation fallacy, where a similarity is equivocated for an identity:

A is similar to B
If we have judgment X about A, then we must have judgment X about B
But it is obviously mistaken to have judgment X about B.
Therefore, we should not have judgment X about A.

Peter Sanger (sp?) seems to use this fallacy:

Cows are similar to babies in that neither are sapient
If we can eat cows, then we can eat babies
But it's absurd to eat babies
Therefore, we should not eat cows.

Sanger ignores that while babies and cows have some similarities, they have differences too, and we can attach moral judgments to the differences.

Craig's fallacy is different. His use of "can" makes the argument valid. If we can define marriage as we please, then, if that were to please us, we can define marriage as applying to man and dog.

Instead, Craig makes a category fallacy, arguing that we can choose whether marriage is objectively real or is socially constructed. But the ontological status of marriage (objective vs. constructed) is itself is a matter of objective truth, not social construction. It's one or the other, regardless of what we choose to believe.