Friday, November 18, 2011

The Slippery Slope Fallacy

Some fallacies are particularly easy to fall into precisely because they rely on a good measure of truth, or even sound reasoning. While that may sound counterintuitive, it’s actually what makes for a great fallacy. Just a good portion of logic and reasoning mixed with the error itself. The fallacy we will discuss today is commonly referred to as the “slippery slope” fallacy. It typically starts with some premise and moves to a horrific or undesirable consequence or series of consequences, thereby showing the premise to be false.

An example would be the following: “once you endorse scholarship, you start to endorse worldly ways of thinking. Then, you’ll believe theories over what a pastor teaches. After that, you’ll end up saying the Bible isn’t true.” Did you catch it? The idea is that by legitimizing scholarship, one will probably or inevitably deny the Bible. But this simply isn’t true. Another example (seen too often in Independent Baptist circles) concerns music. “If you allow a contemporary song to be used in a church service, then the standard of dress is relaxed. When standards of dress are relaxed, then personal morality is lowered. When personal morality is lowered, the church becomes carnal at least and apostate at worst.” So, obviously, singing a contemporary Christian song leads inexorably to carnality.

The reason these types of fallacies work (they are especially popular in political campaigns) is they rely on a rule of logic. The rule is this: If P, then Q. If Q, then R. Therefore, if P, then R. The idea is that if one premise entails another, and that second premise entails a third, then wherever the first is present so will be the third. This is entirely correct so far. So then the slippery slope fallacy is not really fallacious at all, right? Wrong.

While not formally fallacious (that is, it is well within the bounds of actual logic) it is informally so. In our examples, what our arguers need to show is that each and every premise in the chain is present whenever its antecedent is also present. In other words, for the music argument, they need to show every time a contemporary song is introduced, the standard of dress is lowered, and every time the standard of dress is lowered, personal morality suffers, and so on. It won’t do in this case merely to claim it is more probable, for the slippery slope typically purports causal relationships and is not merely descriptive of coextensive but independent events.

Another pitfall for slippery slope fallacies is that they may ignore common causes, rely on controversial premises, or switch the objects of the premise mid-argument. Again, taking our music example: perhaps it is the case (as it is with so many churches) that music standards are relaxed precisely as a rejection of prior legalism (perceived by the church), and hence dress standards are relaxed for the same reason. This would be an example of ignoring a common cause. Relying on controversial premises would include the link that claims relaxing a standard of dress leads to a downgrade in personal morality. I don’t see how anyone could really know this, and I wonder where the studies are. Finally, sometimes this link includes switching the objects of the causal chain. For instance, churches with relaxed (or non-legalistic) music/dress standards tend to attract guests (unbelievers) and non-conformists, the quirky and mundane—in other words, all types of people. Sometimes the “downgrade in morality” is not at all in the person who was legalistic but now is not. In fact, it seems people who make this charge will take the unbelievers and chide them, thinking they are part of the local body!

So how do you avoid committing the slippery slope fallacy? If you make an argument consisting of a logical chain, make sure to avoid these errors, and above all, make sure each part of the chain entails the next one. This reason alone may be why we do not see too many non-fallacious versions of the argument.
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  1. I hear there's two types of slippery slopes: causal slippery slope and logical slippery slope. The causal is fallacious, while the logical isn't. Is this true? Thanks.

  2. Hi Kyle, thanks for commenting! :)

    I havent' actually heard those divisions made, to be honest. But as far as I can tell, yes, "logical slippery slope" is valid. It's because "If P, then Q; if Q, then R; therefore, if P, then R," is true with regards to logical entailment. Of course, then one can always deny R and by modus tollens deny P as well as Q!

    But because of this truth, I don't know that causal slippery slope would always be fallacious. For instance, if we use the above logical links but each link in the chain is causal, and the purported causes really are in fact causes of the consequents, then I don't see how it would be fallacious. However, if by "causal slippery slope," one simply means what we have described in the post above, then I wholeheartedly agree. They've made an informal mistake in reasoning by supposing the antecedents are causally linked to the consequents when nothing of the sort has been shown. Thanks for the interesting thoughts!

  3. Thanks. This is really helpful.

  4. Good! I'm glad to hear it. God bless!


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